Preformulation Preformulation StudiesStudies

By L.T.M. Muungo, PhD, By L.T.M. Muungo, PhD, Pharmaceutist, Pharmaceutist,

Department of Pharmacy, Department of Pharmacy, UNZA, ZambiaUNZA, Zambia

Outline of topicOutline of topic Study of Study of physical properties physical properties of drugs like of drugs like

physical form, particle size, shape, density, physical form, particle size, shape, density, wetting, dielectric constant, solubility, wetting, dielectric constant, solubility, dissolution, organoleptic properties and their dissolution, organoleptic properties and their effect on formulation, stability and effect on formulation, stability and bioavailability.bioavailability.

Study of Study of chemical propertieschemical properties of drugs like of drugs like hydrolysis, oxidation – reduction, hydrolysis, oxidation – reduction, racemisation, polymerization and their racemisation, polymerization and their influence on formulation and stability of influence on formulation and stability of products. products.

Study of Study of prodrugsprodrugs in solving problems related in solving problems related to stability, bioavailability and elegancy of to stability, bioavailability and elegancy of formulation. formulation.

IntroductionIntroductionPreformulation:Preformulation:

• a stage of development during which the a stage of development during which the physicochemical properties of drug substance are physicochemical properties of drug substance are characterized.characterized.

When???When???• If the drug shows sufficient activity in animals & is If the drug shows sufficient activity in animals & is

to be evaluated in humans.to be evaluated in humans.

Focus……Focus……• On physicochemical properties of a new compound On physicochemical properties of a new compound

which may affect the drug performance & which may affect the drug performance & development of efficacious dosage form.development of efficacious dosage form.

Drug Development CycleDrug Development Cycle

The Drug Development Cycle ~ An The Drug Development Cycle ~ An OverviewOverview

The process of developing a new drug can take between 10 The process of developing a new drug can take between 10 and 15 years with an estimated average cost of $800 millionand 15 years with an estimated average cost of $800 million

Discovery/Pre-Clinical TestingDiscovery/Pre-Clinical Testing Time: 6.5 YearsTime: 6.5 YearsPhase IPhase I Time: 1.5 YearsTime: 1.5 YearsPhase II: Safety and EfficacyPhase II: Safety and Efficacy Time: 2 YearsTime: 2 YearsPhase IIIPhase III Time: 3.5 YearsTime: 3.5 YearsMarketing Approval ProcessMarketing Approval Process Time: 1.5 Years Time: 1.5 Years

IntroductionIntroductionProject team –Project team – Representative from Representative from

different disciplinesdifferent disciplinesDifferent DisciplinesDifferent Disciplines

Medicinal Chemistry and PharmacologyMedicinal Chemistry and PharmacologyPre-formulation ResearchPre-formulation ResearchFormulation developmentFormulation developmentProcess R&DProcess R&DAnalytical R&DAnalytical R&DToxicology and drug metabolismToxicology and drug metabolism

Development of a drug Development of a drug candidatecandidate

DeficiencyDeficiency – – Molecular modification Molecular modification to improve drug propertiesto improve drug propertiesSalts eg. Ephedrine HClSalts eg. Ephedrine HClProdrug eg. Erythromycin EstolateProdrug eg. Erythromycin EstolateSolvates, polymorphs etcSolvates, polymorphs etc

Synthesis Synthesis organic media – Purityorganic media – Purity

Compound IdentityCompound Identity

StructureStructure

Formula & Mo. Wt.Formula & Mo. Wt.

Therapeutic IndicationTherapeutic Indication•Probable Human DoseProbable Human Dose•Desired Dosage Form(s)Desired Dosage Form(s)•Bioavailability Model(s)Bioavailability Model(s)•Comparative ProductsComparative Products

Potential HazardsPotential Hazards

Initial Bulk LotsInitial Bulk Lots•Lot NumberLot Number•Crystallization Solvent(s)Crystallization Solvent(s)•Particle Size RangeParticle Size Range•Melting PointMelting Point•% Volatiles% Volatiles•ObservationsObservations

Analytical MethodsAnalytical Methods•HPLC AssayHPLC Assay•TLC AssayTLC Assay•UV/VIS SpectroscopyUV/VIS Spectroscopy•Synthetic RouteSynthetic Route•Probable Decay ProductsProbable Decay Products

Key DatesKey Dates•Bulk Scale upBulk Scale up•Toxicology Start DateToxicology Start Date•Clinical Supplies PreparationClinical Supplies Preparation•IND FilingIND Filing•Phase I TestingPhase I Testing

Critical development Issue(s)Critical development Issue(s)

Essential information helpful in designing preformulation evaluation of a new drugEssential information helpful in designing preformulation evaluation of a new drug

I

II

III

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VI

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VII

VIII

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Drug Drug DiscoveryDiscovery Literature Search Literature Search

Preliminary DataPreliminary Data•Stability assay•Key Stability Data•Key solubility Data

Molecular OptimizationMolecular OptimizationSalts & solvates Prodrugs

Evaluation & Selection of Evaluation & Selection of DrugDrug

Formulation RequestFormulation Request

Physical Physical CharacterizationCharacterization•Bulk properties•Solubility profile•Stability profile

Formulation Formulation DevelopmentDevelopment

•Compatibility & Stability•Dissolution•Bioavailability

Phase I Phase I FormulationFormulation•IND Stability•Bioavailability•Scale-up

Investigational New Drug (IND) Application Investigational New Drug (IND) Application

Process ResearchProcess Research•Improve Yield•Alternate route•Produce bulk

Process DevelopmentProcess Development•Bulk scale-up

Analytical Analytical ResearchResearch•Assay development

Analytical ResearchAnalytical Research•Bulk clearance•Toxicity potency•Formulation assay•IND formulation stability

BioavailabilityBioavailability•In-vivo models

ToxicologyToxicology•Acute•Chronic

Preformulation studies are an important foundation tool Preformulation studies are an important foundation tool early in the development of both API and drug products. early in the development of both API and drug products.

They influence…. They influence…. Selection of the drug candidate itselfSelection of the drug candidate itself Selection of formulation componentsSelection of formulation components API & drug product manufacturing processesAPI & drug product manufacturing processes Determination of the most appropriate container / Determination of the most appropriate container /

closure systemclosure system Development of analytical methodsDevelopment of analytical methods Assignment of API retest periodsAssignment of API retest periods The synthetic route of the APIThe synthetic route of the API Toxicological strategic management processToxicological strategic management process

Why preformulation studies are Why preformulation studies are required?required?

Preformulation CharacterizationPreformulation CharacterizationBulk propertiesBulk properties

OrganolepticOrganoleptic crystallinity and polymorphismcrystallinity and polymorphism water adsorptionwater adsorption particle size, shape, and particle size, shape, and

surface areasurface area bulk densitybulk density AdhesionAdhesion powder flowpowder flow compressibilitycompressibility

Physico-chemical propertiesPhysico-chemical properties solubility analysissolubility analysis IonizationIonization partition coefficientspartition coefficients dissolutiondissolution

StabilityStability•solid state (RH, oxygen, light, compatibility)solid state (RH, oxygen, light, compatibility)

•solution (pH, buffers, solvent, temperature)solution (pH, buffers, solvent, temperature)

•compatibility with excipients (other additives)compatibility with excipients (other additives)

Biopharmaceutical propertiesBiopharmaceutical properties•absorption (route, rate, extent, mechanism, absorption (route, rate, extent, mechanism,

absorption windows, food effects)absorption windows, food effects)

•metabolism (first pass metabolism, enzyme metabolism (first pass metabolism, enzyme

induction, metabolism in GIT)induction, metabolism in GIT)

•duration of action (dosing, controlled release)duration of action (dosing, controlled release)

•dosedose

Any QuestionsAny Questions

Investigative Procedures on Pre-formulation Characteristic

contents as Examples

Objective Objective Quantitation of physical chemical Quantitation of physical chemical

properties that will assist in developing a properties that will assist in developing a stable, safe and effective formulation with stable, safe and effective formulation with maximum bioavailabilitymaximum bioavailability

Principal areas ofPrincipal areas of Pre-formulations Pre-formulations

Bulk CharacterizationBulk Characterization

Solubility AnalysisSolubility Analysis

Stability AnalysisStability Analysis

Principal areas of PreformulationsPrincipal areas of Preformulations Bulk CharacterizationBulk Characterization

Crystallinity and polymorphismCrystallinity and polymorphism

HygroscopicityHygroscopicity

Fine particle characterizationFine particle characterization

Bulk densityBulk density

Powder flow propertiesPowder flow properties

Bulk CharacterizationBulk Characterization Synthetic process simultaneously developedSynthetic process simultaneously developed A drug candidate A drug candidate – Solid form not identified – – Solid form not identified –

emerge of new polymorphsemerge of new polymorphs Solid form Solid form – particle size, bulk density and – particle size, bulk density and

surface morphology – Process developmentsurface morphology – Process development Comprehensive characterization Comprehensive characterization – To avoid – To avoid

misleading predictions of stability or solubility, misleading predictions of stability or solubility, which depends on a particular crystalline form which depends on a particular crystalline form

Crystallinity and polymorphismCrystallinity and polymorphismCrystal habit and the internal structure Crystal habit and the internal structure

affects the bulk and physiochemical affects the bulk and physiochemical properties properties

Flowability to chemical stabilityFlowability to chemical stabilityHabitHabit – Description of the outer – Description of the outer appearance of a crystal appearance of a crystal

Eg: Acicular or needle, platy, massive, Eg: Acicular or needle, platy, massive, tabular etctabular etc

Internal structure : Internal structure : Molecular Molecular arrangement within the solidarrangement within the solid

Crystallinity and polymorphismCrystallinity and polymorphism Changes in internal structure for a Changes in internal structure for a

compound – Alter change in the crystal compound – Alter change in the crystal habit. habit.

Characterisation Involves –Characterisation Involves – Verifying the solid is the expected chemical Verifying the solid is the expected chemical

compoundcompound Characterization the internal structureCharacterization the internal structure Describing the habit of the crystal Describing the habit of the crystal

Prismatic

Bladed

Habit and Crystal chemistry of a Habit and Crystal chemistry of a compoundcompoundChemical CompoundChemical Compound

HabitHabit Internal structureInternal structure

AmorphousAmorphousCrystallineCrystalline

Single entitySingle entity

PolymorphsPolymorphs

Molecular AdductsMolecular Adducts

Non Stoichiometric inclusion Non Stoichiometric inclusion compoundscompounds

Stoichiometric Stoichiometric Solvates Solvates (Hydrates), (Hydrates),

LayerLayer Channel Cage Cage (Clathrate)(Clathrate)

Crystallinity and Crystallinity and polymorphismpolymorphism Crystals Crystals

Repetitious spacing Repetitious spacing of constituent atoms or of constituent atoms or molecules in 3 dimensional arraymolecules in 3 dimensional array

Amorphous Amorphous Have atoms or molecules Have atoms or molecules randomly placedrandomly placed, ,

prepared byprepared by Rapid precipitationRapid precipitation LyophilizationLyophilization Rapid cooling of liquid meltsRapid cooling of liquid melts

Amorphous – Higher thermodynamic energy, Amorphous – Higher thermodynamic energy, solubilites and dissolutions is also high.solubilites and dissolutions is also high.Upon storage – Tends to revert more stable Upon storage – Tends to revert more stable

forms forms Disadv.: Thermodynamic instabilityDisadv.: Thermodynamic instability

Crystallinity and Crystallinity and polymorphismpolymorphism

Crystalline –Crystalline – Nonstoichiometric adducts – entrapped Nonstoichiometric adducts – entrapped

solvents within crystals. Eg.: Inclusionssolvents within crystals. Eg.: InclusionsUndesirable, Lack of reproducibility – AvoidedUndesirable, Lack of reproducibility – Avoided

Stoichiometric adducts – As a solvate, is a Stoichiometric adducts – As a solvate, is a molecular complex that has incorporated molecular complex that has incorporated the crystalline solvent molecules into the crystalline solvent molecules into specific sites within crystal latticespecific sites within crystal lattice

Eg.: water ( hydrate- monohydrate)Eg.: water ( hydrate- monohydrate)Aq. Solubilities, Eg AmpicillinAq. Solubilities, Eg AmpicillinDissolution - bioavailabilityDissolution - bioavailability

CrystallinityCrystallinity Conversion of an anhydrous Conversion of an anhydrous compound to a hydrate within the compound to a hydrate within the dosage form may reduce the dosage form may reduce the dissolution rate & extent of drug dissolution rate & extent of drug absorption.absorption.

PolymorphismPolymorphism Ability of a compound or element to crystallize as more Ability of a compound or element to crystallize as more

than one distinct crystalline species with than one distinct crystalline species with different internal different internal lattices.lattices.

Chemical stability and solubility – Drug’s bioavailabilityChemical stability and solubility – Drug’s bioavailability Physicochemical parameter that alterPhysicochemical parameter that alter

Melting pointMelting point DensityDensity Hardness, crystal shape, optical propertiesHardness, crystal shape, optical properties

Eg.: Chloramphenicol PalmitateEg.: Chloramphenicol Palmitate 3 crystalline polymorphic forms, A,B,C and amorphous 3 crystalline polymorphic forms, A,B,C and amorphous

formform Physicochemical properties vary : MP, Density, Physicochemical properties vary : MP, Density,

hardness, optical properties etchardness, optical properties etc

PolymorphismPolymorphism Chemical stability & solubility changes Chemical stability & solubility changes

due to polymorphism can have an impact due to polymorphism can have an impact on drug’s bioavailability & its development on drug’s bioavailability & its development program.program.

e.g. Chloramphenicol Palmitate exist in 3 e.g. Chloramphenicol Palmitate exist in 3 crystalline polymorphic forms (A, B & C), crystalline polymorphic forms (A, B & C), “peak” serum levels increased substantially as “peak” serum levels increased substantially as a function of the % of form B polymorph, the a function of the % of form B polymorph, the more soluble polymorph. more soluble polymorph.

Characterization of polymorphic & Characterization of polymorphic & solvated forms involves quantitative solvated forms involves quantitative analysis of these differing analysis of these differing physicochemical properties.physicochemical properties.

% of Form B

PolymorphismPolymorphismClassification-Classification-1.1. Monotropic polymorphs -Monotropic polymorphs - one stable crystal form and one stable crystal form and

one meta stable regardless of temperature changeone meta stable regardless of temperature changeOROR

Only one polymorph is stable at all reasonable Temp.Only one polymorph is stable at all reasonable Temp. Eg. Glyceryl stearates, metalazoneEg. Glyceryl stearates, metalazone

2. Enantiotropic polymorphs2. Enantiotropic polymorphs - One polymorph is stable - One polymorph is stable over one temperature range, another polymorph is over one temperature range, another polymorph is stable over a different temperature rangestable over a different temperature range

E.g. carbamazepine and acetazolamine,SulfurE.g. carbamazepine and acetazolamine,Sulfur

PolymorphismPolymorphismPreformulation study-Preformulation study- - identifies polymorph stable at room temp- identifies polymorph stable at room temp - stability of polymorph in dosage form- stability of polymorph in dosage form

Analytical Method Material req.

MicroscopyFusion MethodDSCIRX-ray powder diffractionSEMTGADissolution/ solubility analysis

1mg1mg2-5 mg2-20 mg500 mg2 mg10 mgMg to gm

Analytical method for Analytical method for characterization of polymorphcharacterization of polymorph

1.1. Microscopy-Microscopy-

Hot stage microscopyHot stage microscopyMicrographs taken at a heating rate of 10Micrographs taken at a heating rate of 1088C/minC/min

(a) 30.0(a) 30.088C, (b) 156.5C, (b) 156.588C, (c) 162.5C, (c) 162.588C, (d) 166.2C, (d) 166.288C,C,(e) 168.5(e) 168.588C and (f) 170.5C and (f) 170.588C.C.

Thermal AnalysisThermal Analysis1. DSC- 1. DSC- measures Heat Loss/ Gain resultingmeasures Heat Loss/ Gain resulting from chemical or physical changesfrom chemical or physical changes2. TGA- 2. TGA- measures changes in sample measures changes in sample

weight as a function of time/ temp weight as a function of time/ tempEg. Endothermic reaction-Eg. Endothermic reaction- Exothermic reactions-Exothermic reactions-

Eg. Anhydrous, Dihydrate formEg. Anhydrous, Dihydrate form

3. X-ray diffraction3. X-ray diffraction When X-rays interact with a When X-rays interact with a crystalline crystalline

substance (Phase), one gets a diffraction substance (Phase), one gets a diffraction pattern. pattern. The X-ray diffraction pattern of a The X-ray diffraction pattern of a pure substance is, therefore, like a fingerprint pure substance is, therefore, like a fingerprint of the substance.of the substance.

4. Additional techniques used are- NMR, SEM, 4. Additional techniques used are- NMR, SEM, IRIR

Scanning electron microscopy Scanning electron microscopy (SEM)(SEM)

HygroscopicityHygroscopicity FactorsFactors

Adsorption & equilibrium moisture content depends uponAdsorption & equilibrium moisture content depends upon Atmospheric humidityAtmospheric humidity TemperatureTemperature Surface AreaSurface Area Exposure & mechanism for moisture uptakeExposure & mechanism for moisture uptake

TypesTypes DeliquescentDeliquescent: : adsorbs sufficiently water to dissolves completelyadsorbs sufficiently water to dissolves completely HygroscopicHygroscopic: adsorb water and forms hydrate: adsorb water and forms hydrate

Changes in moisture level affectsChanges in moisture level affects Chemical stabilityChemical stability Flow abilityFlow ability CompactibilityCompactibility

HygroscopicityHygroscopicity Normalized or percentage weight gain data from Normalized or percentage weight gain data from

these hygroscopic studies are plotted against these hygroscopic studies are plotted against time to predict stability studies.time to predict stability studies.

Karl Fischer titration, gas chromatography, TGAKarl Fischer titration, gas chromatography, TGA

Based on data, Specific handling during Based on data, Specific handling during manufacturing (Humidity control) / special manufacturing (Humidity control) / special storage (Dessicant)can be recommended.storage (Dessicant)can be recommended.

Fine Particle CharacterizationFine Particle CharacterizationBulk flow, formulation homogeneity and Bulk flow, formulation homogeneity and

surface area controlled processes such surface area controlled processes such as dissolution.as dissolution.

MicroscopyMicroscopyCoulter counter Coulter counter Sieve methodSieve methodBET method (Surface area)BET method (Surface area)SEM methodSEM method

Coulter counterCoulter counter

A Coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. A typical Coulter counter has one or more microchannels that separate two chambers containing electrolyte solutions. As fluid containing particles or cells is drawn through each microchannel, each particle causes a brief change to the electrical resistance of the liquid. The counter detects these changes in electrical resistance.

BET methodBET methodBraunner, Emmett and Teller methodBraunner, Emmett and Teller methodLayer of nitrogen is adsorbed on the Layer of nitrogen is adsorbed on the

sample surface at -196°C (until surface sample surface at -196°C (until surface adsorption reach equillibrium)adsorption reach equillibrium)

Sample is heated to room temperature- N2 Sample is heated to room temperature- N2 desorbs and its volume is measured and desorbs and its volume is measured and converted to no. of adsorbed molecule via converted to no. of adsorbed molecule via ideal gas law (PV=nRT)ideal gas law (PV=nRT)

Each N2- 16AEach N2- 16A22

Bulk DensityBulk Density Bulk density :Bulk density :

Varies with Method of crystallization, Varies with Method of crystallization, milling or formulationmilling or formulation

High dose – Size of capsulesHigh dose – Size of capsulesLow dose - homogeneity Low dose - homogeneity Drug and excipientsDrug and excipients

Tapped densityTapped density True densityTrue density

Powder Flow propertiesPowder Flow properties

Powder Flow properties: Free flowing or cohesive

Factors affecting are- particle size, density, shape, moisture content, electrostatic charge

-Flow rates (g/sec)-Compressibility Index-Angle of repose

Way to improve flow properties-Granulation -Slugging/ compaction-Glident

Any QuestionsAny Questions

Principal areas of Pre-formulations-Principal areas of Pre-formulations-Solubility AnalysisSolubility Analysis

Ionization constant –pKaIonization constant –pKa

pH solubility profilepH solubility profile

Common ion effect – KspCommon ion effect – Ksp

Thermal effectsThermal effects

SolubilizationSolubilization

Partition co-efficientPartition co-efficient

DissolutionDissolution

Solubility AnalysisSolubility Analysis

What is solubility??What is solubility??

Factors affecting solubilityFactors affecting solubility

Saturation solubilitySaturation solubility

What is Dissolution??What is Dissolution??

Very soluble less than 1 part   Freely soluble from 1 to 10 parts   Soluble from 10 to 30 parts   Sparingly soluble from 30 to 100 parts   Slightly soluble from 100 to 1000 parts   Very slightly soluble from 1000 to 10,000 parts   Practically insoluble more than 10,000 parts    

Solubility AnalysisSolubility Analysis

Solubility AnalysisSolubility Analysis

Solubility study done in various solventsSolubility study done in various solvents -Aqueous solvent-Aqueous solvent - water, buffers- water, buffers -Nonaqueous solvents-Nonaqueous solvents - Organic solvents- Organic solvents - Glycerol, PEG- Glycerol, PEG

Solubility AnalysisSolubility Analysis Focus on drug-solvent system that could Focus on drug-solvent system that could

occur during the delivery of the drug occur during the delivery of the drug candidatecandidate

Provides basis for formulation work.Provides basis for formulation work. Determination ofDetermination of

pKapKaTemperature dependenceTemperature dependencepH solubility profilepH solubility profileSolubility productsSolubility productsSolubilization mechanismsSolubilization mechanismsRate of dissolutionRate of dissolution

Solubility AnalysisSolubility Analysis Analytical methods useful includeAnalytical methods useful include

HPLCHPLCUV SpectroscopyUV SpectroscopyFluoroscence SpectroscopyFluoroscence SpectroscopyReverse Phase gas chromatographyReverse Phase gas chromatography

Factors to be defined for solubility and Factors to be defined for solubility and Dissolution study -Dissolution study -pHpHTemperatureTemperatureBuffer concentrationsBuffer concentrations

pKapKa DeterminationDeterminationDissociation constant is capability of drug Dissociation constant is capability of drug

to ionize within pH range of 1 to 10to ionize within pH range of 1 to 10Solubility & absorption alteredSolubility & absorption alteredHenderson-Hasselbalch equationHenderson-Hasselbalch equation

Acidic compoundsAcidic compounds

Basic CompoundsBasic Compounds

pKapKa Determination Determination contd..contd..

Absorption PrinciplesAbsorption Principles

Weakly acidic drug pka > 3, unionized form in the Weakly acidic drug pka > 3, unionized form in the stomach , Drug is ionized predominantly in stomach , Drug is ionized predominantly in intestine.intestine.

Basic drug pka=8-10, ionized form predominantly Basic drug pka=8-10, ionized form predominantly in stomach & intestinein stomach & intestine

Eg. ErythromycinEg. Erythromycin

- Other factors like lipid solubility, dissolution rate, - Other factors like lipid solubility, dissolution rate, common ion effects, metabolism also affectscommon ion effects, metabolism also affects

pKapKa DeterminationDeterminationcontd..contd.. Determination of pKaDetermination of pKa

Analytical methodsAnalytical methodsDetermination of spectral shifts by UV or Visible spectroscopy Determination of spectral shifts by UV or Visible spectroscopy (Dilute aq. Solution can be analyzed directly)(Dilute aq. Solution can be analyzed directly)

Potentiometric TitrationPotentiometric Titration(pKa range of 3-10)(pKa range of 3-10)

Factors affecting pKaFactors affecting pKa BufferBuffer TemperatureTemperature Ionic StrengthIonic Strength Co-solventCo-solvent

Effect of TemperatureEffect of Temperature Solution ProcessSolution Process Endothermic Endothermic

Heat of solution is positiveHeat of solution is positive Exothermic Exothermic

Heat of solution is negative ( lithium salts)Heat of solution is negative ( lithium salts)

Non-electrolytes & ionized forms Non-electrolytes & ionized forms ΔΔH between 4 to 8 H between 4 to 8 kcal/molkcal/mol

Salt forms of drugs -2 to 2 kcal/mole (less sensitive to Salt forms of drugs -2 to 2 kcal/mole (less sensitive to temp.)temp.)

Effect solution dosage form design & storage condition.Effect solution dosage form design & storage condition. Solvent systems including co-solvents.Solvent systems including co-solvents. MicellesMicelles ComplexationComplexation

Heat of solution – solubility values for saturated Heat of solution – solubility values for saturated solutions equilibrated at controlled temperaturesolutions equilibrated at controlled temperature Range: 5°C, 25°C, 37°C, 50°CRange: 5°C, 25°C, 37°C, 50°C lnS = -lnS = -∆Hs/R (1/T)+C∆Hs/R (1/T)+CWhere S = molar solubility at temperature T kelvinWhere S = molar solubility at temperature T kelvin R = gas constant R = gas constant ΔΔHHs s = Heat of solution= Heat of solution Semi log plot solubility vs reciprocal temperature Semi log plot solubility vs reciprocal temperature

ΔΔHHss obtained from slope obtained from slope Salt forms of drugs – less sensitive Salt forms of drugs – less sensitive ΔΔHHss : -2 to +2kcal/mol : -2 to +2kcal/mol Unionized form of weak acids/ bases dissolved in water Unionized form of weak acids/ bases dissolved in water ΔΔHHss : 4-8kcal/mole : 4-8kcal/mole

SolubilizationSolubilization Increasing the solubility of a Increasing the solubility of a

drug by addition of third drug by addition of third agent (solubilizing agent) is agent (solubilizing agent) is called as solubilizationcalled as solubilization

Addition of co-solvent to the Addition of co-solvent to the aqueous system like aqueous system like ethanol, propylene glycol, & ethanol, propylene glycol, & glyceringlycerin

Act by disrupting the Act by disrupting the hydrophobic interactions at hydrophobic interactions at the nonpolar solute/water the nonpolar solute/water interface.interface. Fig: Solubility of hydrocortisone & hydrocortisone 21-Fig: Solubility of hydrocortisone & hydrocortisone 21-

heptonoate in propylene glycol-water mixturesheptonoate in propylene glycol-water mixtures

Partition CoefficientPartition Coefficient

Ratio of unionized drug distributed Ratio of unionized drug distributed between the organic & inorganic aqueous between the organic & inorganic aqueous phase at equilibrium.phase at equilibrium.

ImportanceImportanceScreening for biological activityScreening for biological activityDrug deliveryDrug delivery

System used areSystem used areOctanol/water and Chloroform/waterOctanol/water and Chloroform/water

pH Solubility Profile & Common Ion pH Solubility Profile & Common Ion EffectsEffects

Solubility of an acidic or basic drug Solubility of an acidic or basic drug depends on depends on pKa of the ionizing functional group & pKa of the ionizing functional group & intrinsic solubilities for both the ionized & intrinsic solubilities for both the ionized &

unionized forms.unionized forms.

Experimental determination of a solubility Experimental determination of a solubility product should include measurement of product should include measurement of pH as well as assays of both drug & pH as well as assays of both drug & counter ion concentrations.counter ion concentrations.

DissolutionDissolution Release of drug from a dosage form involves diverse factors Release of drug from a dosage form involves diverse factors

as:as: A drug is expected to be release from the solid dosage forms A drug is expected to be release from the solid dosage forms

(granules, tablets, capsules etc) & immediately go into (granules, tablets, capsules etc) & immediately go into molecular solutionmolecular solution. This process is called . This process is called dissolutiondissolution..

Dissolution (Dissolution (molecular dispersionmolecular dispersion) is a prerequisite for the drug ) is a prerequisite for the drug absorption.absorption.

APPLICATIONAPPLICATION The dissolution test is used as a The dissolution test is used as a quality control toolquality control tool to monitor to monitor

routinely the uniformity & reproducibility of production batches.routinely the uniformity & reproducibility of production batches. The test is utilized as a The test is utilized as a research toolresearch tool for optimizing the parameters & for optimizing the parameters &

ingredients in new formulations.ingredients in new formulations. Whenever Whenever in vitro in vitro && in vivo in vivo correlationcorrelation are observed, the dissolution are observed, the dissolution

studies are used as tools to substitute the frequent studies of studies are used as tools to substitute the frequent studies of bioabsorption.bioabsorption.

Dissolution Dissolution contd…contd…

Dissolution is expressed in terms of Dissolution is expressed in terms of a rate processa rate process.. Greater the rate, faster the dissolution.Greater the rate, faster the dissolution. Dissolution rate may be defined as “Dissolution rate may be defined as “the amount of drug the amount of drug

substance that goes into solution per unit time under substance that goes into solution per unit time under standardized conditions of liquid/solid interface, standardized conditions of liquid/solid interface, temperature & solvent compositiontemperature & solvent composition”. ”.

Noyes-Whitney’s equationNoyes-Whitney’s equation is useful for estimating the rate is useful for estimating the rate of dissolution.of dissolution.dC / dt = DA/ hV (CdC / dt = DA/ hV (Css -C) -C)

DISSOLUTION TESTING CONDITIONSDISSOLUTION TESTING CONDITIONS ApparatusApparatus Dissolution MediumDissolution Medium AgitationAgitation ValidationValidation

DISSOLUTION APPARATUSDISSOLUTION APPARATUSThe most commonly employed dissolution test methods are (1) the basket method (Apparatus 1)

(2) the paddle method (Apparatus 2)

The basket and the paddle methods are simple, robust, well standardized, and used worldwide. These methods are flexible enough to allow dissolution testing for a variety of drug products.

Apparatus 1 and Apparatus 2 should be used unless shown to be unsatisfactory. The in vitro dissolution procedures, such as

(3) the reciprocating cylinder (Apparatus 3) and (4) a flow-through cell system (Apparatus 4)

described in the USP, may be considered if needed.

These methodologies or other alternatives/modifications should be considered on the basis of their proven superiority for a particular product.

Dissolution Dissolution

basket method basket method (Apparatus 1)(Apparatus 1)

Paddle method Paddle method (Apparatus 2)(Apparatus 2)

reciprocating cylinder reciprocating cylinder (Apparatus 3)(Apparatus 3)

flow-through cell flow-through cell system (Apparatus 4)system (Apparatus 4)

Any Questions

Principal areas of PreformulationsPrincipal areas of Preformulations

Stability AnalysisStability Analysis

Stability in toxicology formulationsStability in toxicology formulations

Solubility stabilitySolubility stability

pH rate profilepH rate profile

Solid state stabilitySolid state stability

Bulk stabilityBulk stability

CompatibilityCompatibility

Stability AnalysisStability AnalysisStability Analysis requirementStability Analysis requirementStability in toxicology Stability in toxicology

formulationsformulationsSolution stabilitySolution stability

pH rate profilepH rate profileSolid state stability Solid state stability

Bulk stabilityBulk stabilityCompatibilityCompatibility

Stability AnalysisStability Analysis Preformulation studies give first Preformulation studies give first quantitative quantitative

assessment assessment of chemical stability of a new of chemical stability of a new drug.drug.

Solution State Solid Solution State Solid State State

Handling, formulation, storage and Handling, formulation, storage and administration of a drug candidateadministration of a drug candidate

Test protocols & experimental methods Test protocols & experimental methods Assay – intact drug and degraded productAssay – intact drug and degraded product

Evaluation – HPLC, Gas ChromatographyEvaluation – HPLC, Gas ChromatographyDegradation studyDegradation study

StabilityStability in toxicology in toxicology formulationsformulations

Since toxicological studies typically commence early Since toxicological studies typically commence early in drug development, it is often advisable to in drug development, it is often advisable to evaluate samples of toxicology preparations for evaluate samples of toxicology preparations for Stability and potential homogeneity problemsStability and potential homogeneity problems

Drug administered – Feed or oral gavage of solution Drug administered – Feed or oral gavage of solution or suspension of drug in an aqueous vehicleor suspension of drug in an aqueous vehicle

Minerals, vitamins, enzymes , a multitude of Minerals, vitamins, enzymes , a multitude of functional groups present in feed – reduces shelf life functional groups present in feed – reduces shelf life of drugof drug

Fresh sample of feed to be usedFresh sample of feed to be used Solution or suspension – Checked for ease of Solution or suspension – Checked for ease of

manufacture manufacture Stored in a flame sealed ampoules at various Stored in a flame sealed ampoules at various

temperaturestemperaturesOccasionaly shaking – DispersabilityOccasionaly shaking – Dispersability

SolutionSolution StabilityStability Aim-Aim-Identification of conditions necessary to form a Identification of conditions necessary to form a

stable solutionstable solution Study Includes – effects of pH, Ionic strength, Co-Study Includes – effects of pH, Ionic strength, Co-

solvent, light , temperature and oxygensolvent, light , temperature and oxygen Probing experiments at extremes conditions of pH Probing experiments at extremes conditions of pH

and temperature (0.01N HCl , water ,0.01N, NaOH and temperature (0.01N HCl , water ,0.01N, NaOH all at 90°C).all at 90°C).

Assay specificity and Maximum rates of degradationAssay specificity and Maximum rates of degradation Complete pH rate profile – pH of max stability.Complete pH rate profile – pH of max stability. Aq. Buffers are used to provide wide range with Aq. Buffers are used to provide wide range with

constant levels of drug, co solvent and ionic constant levels of drug, co solvent and ionic strength strength

Compatible with physiological mediaCompatible with physiological media Eg.: Ionic strength ( µ) of 0.9% NaCl is 0.15Eg.: Ionic strength ( µ) of 0.9% NaCl is 0.15 Equation: µ = ½ ∑mEquation: µ = ½ ∑miiZZii

22

mmi = i = molar conc. of the ion, with valence Zimolar conc. of the ion, with valence Zi

Solution StabilitySolution Stability Procedure- Procedure- Stability solutions : Flint glass ampoules, flame Stability solutions : Flint glass ampoules, flame

sealed – prevent evaporation, Stored at sealed – prevent evaporation, Stored at temperature not exceeding its Boiling Point (if temperature not exceeding its Boiling Point (if organic co-solvents are used).organic co-solvents are used).

Varied temp- Varied temp- Activation energyActivation energy Light stability Light stability – protective packing – protective packing

Amber – yellow –green glass containersAmber – yellow –green glass containers Wrapped in aluminium foil or cardboard packagesWrapped in aluminium foil or cardboard packages

Potential for oxidation:Potential for oxidation: Excessive headspace of OExcessive headspace of O22 Excessive headspace with inert gas Excessive headspace with inert gas Inorganic antioxidant – Sodium metabisulfiteInorganic antioxidant – Sodium metabisulfite Organic antioxidant – Butylated hydroxytoluene BHTOrganic antioxidant – Butylated hydroxytoluene BHT

Solution StabilitySolution StabilitypH rate profile pH rate profile

Stability data at each pH and Stability data at each pH and temperaturetemperature

Analyzed kinetically – apparent decay Analyzed kinetically – apparent decay constantconstant

Arrhenius plot – log of apaprent decay Arrhenius plot – log of apaprent decay rate constant Vs reciprocal of absolute rate constant Vs reciprocal of absolute temperaturetemperature

Energy of activation Energy of activation

Solid state stabilitySolid state stability Aim: Identifications of stable storage Aim: Identifications of stable storage

conditions for drug in the solid state conditions for drug in the solid state and identification of compatible and identification of compatible excipients for a formulations.excipients for a formulations.

Affected by change in purity and crystallinityAffected by change in purity and crystallinity Initial bulk lots and newer lots– to be studiedInitial bulk lots and newer lots– to be studied Solid state is slower and difficult to interpret than Solid state is slower and difficult to interpret than

solution statesolution state TLC, UV-Vis, fluorescenceTLC, UV-Vis, fluorescence Polymorphic changes – DSC, IR or appearance Polymorphic changes – DSC, IR or appearance

changes like oxidation – surface discolorationchanges like oxidation – surface discoloration

Procedure:Procedure: Open screw cap vials – Exposed to Open screw cap vials – Exposed to various conditions Temp., Humidity and light upto various conditions Temp., Humidity and light upto 12weeks12weeks

Samples – 5-10mg(HPLC), 10-50mg for DSCSamples – 5-10mg(HPLC), 10-50mg for DSC

Solid State StabilitySolid State StabilityStorage conditionsStorage conditions1.1. Refrigerator- 5°C Refrigerator- 5°C 2.2. Room temp.- 22°C Room temp.- 22°C 3.3. Ambient humidity, 70% RH, 90%RHAmbient humidity, 70% RH, 90%RH4.4. 25°C/60% RH, 40°C/75% RH,25°C/60% RH, 40°C/75% RH,

5.5. Light- Clear, Amber, yellow-green Light- Clear, Amber, yellow-green glass, control sampleglass, control sample

6.6. Ambient humidity- O2 headspace, Ambient humidity- O2 headspace, N2 headspaceN2 headspace

Elevated temperature studiesElevated temperature studies The elevated temperatures commonly used are The elevated temperatures commonly used are

40, 50, and 60 degree centigrade with ambient 40, 50, and 60 degree centigrade with ambient humidity. humidity.

The samples stored at highest temperature are The samples stored at highest temperature are observed observed weekly for physical and  chemical weekly for physical and  chemical changes changes and compared to an appropriate and compared to an appropriate control . control .

If a substantial change is seen, samples stored If a substantial change is seen, samples stored at lower temperature are examined . at lower temperature are examined .

If no changes is seen after 30 days at 60°C , the If no changes is seen after 30 days at 60°C , the stability prognosis is excellent.stability prognosis is excellent.

Stability under high Stability under high humidity conditionshumidity conditions

Solid drug samples can be exposed to Solid drug samples can be exposed to different relative humidity conditionsdifferent relative humidity conditions by by keeping them in laboratory desiccators keeping them in laboratory desiccators containing saturated solutions of various containing saturated solutions of various salts. salts.

The The closed desiccators closed desiccators in turn are kept in in turn are kept in oven to provide constant temperature. oven to provide constant temperature.

The preformulation data of this nature are The preformulation data of this nature are useful in determining if the material should useful in determining if the material should be protected and stored in controlled be protected and stored in controlled low low humidity environment humidity environment or if or if non aqueous non aqueous solvent solvent be used during formulation. be used during formulation.

Photolytic stabilityPhotolytic stability Many drugs fade or dorpen on exposure light. Many drugs fade or dorpen on exposure light. Increased Impurity levelIncreased Impurity level Samples should be exposed to light providing an Samples should be exposed to light providing an

overall illumination of overall illumination of not less than 1.2 million not less than 1.2 million lux hours lux hours and an integrated near ultraviolet and an integrated near ultraviolet energy of not less than energy of not less than 200 watt hours/square 200 watt hours/square metermeter

If If protected samples protected samples (e.g., wrapped in aluminum (e.g., wrapped in aluminum foil) are used as dark controls to evaluate the foil) are used as dark controls to evaluate the contribution of thermally induced change to the contribution of thermally induced change to the total observed change, these should be placed total observed change, these should be placed alongside the authentic sample.alongside the authentic sample.

Resulting data may be useful in determining if an Resulting data may be useful in determining if an amber colored container is required or if color amber colored container is required or if color masking bye should be used in the formulation masking bye should be used in the formulation

Stability to OxidationStability to OxidationDrug’s sensitivity to oxidation can be examined Drug’s sensitivity to oxidation can be examined

by exposing it to atmosphere of high oxygen by exposing it to atmosphere of high oxygen tension. tension.

Usually a 40% oxygen atmosphere allows for Usually a 40% oxygen atmosphere allows for rapid evaluation. rapid evaluation.

Samples are kept in desiccators equipped with Samples are kept in desiccators equipped with three-way stop cocks, which are alternatively three-way stop cocks, which are alternatively evacuated and flooded with desired atmosphere. evacuated and flooded with desired atmosphere.

The process is repeated 3 or 4 times to ensure The process is repeated 3 or 4 times to ensure 100% desired atmosphere. 100% desired atmosphere.

Results may be useful in predicting if an Results may be useful in predicting if an antioxidant is required in the formulation or if the antioxidant is required in the formulation or if the final product should be packaged under inert final product should be packaged under inert atmospheric conditions.atmospheric conditions.

Compatibility studiesCompatibility studiesThe knowledge of The knowledge of drug excipients drug excipients

interaction interaction is useful for the formulation to is useful for the formulation to select appropriate excipients. select appropriate excipients.

The described preformulation screening of The described preformulation screening of drug excipients interaction requires only drug excipients interaction requires only 5mg of drug in a 50% mixture with the 5mg of drug in a 50% mixture with the excipients to maximize the likelihood of excipients to maximize the likelihood of obscuring an interaction . obscuring an interaction .

Mixtures should be examined for Mixtures should be examined for physicochemical properties like appearance, physicochemical properties like appearance, Assay and degradation products.Assay and degradation products.

Formulation Formulation RecommendationRecommendation

Upon the completion of preformulation Upon the completion of preformulation evaluation of a new drug candidate, it is evaluation of a new drug candidate, it is recommended that a recommended that a comprehensive comprehensive report report to be prepared highlighting the to be prepared highlighting the pharmaceutical problems associated pharmaceutical problems associated with this molecule.with this molecule.

This report should conclude with This report should conclude with recommendations for developing recommendations for developing phase I phase I formulationsformulations..

These reports are extremely important in These reports are extremely important in preparing regulatory documents & aid in preparing regulatory documents & aid in developing subsequent drug candidates.developing subsequent drug candidates.

Any QuestionsAny Questions

Principal areas of PreformulationsPrincipal areas of Preformulations

Outline of topicOutline of topicStudy of chemical properties of drugs like Study of chemical properties of drugs like

hydrolysis, oxidation – reduction, hydrolysis, oxidation – reduction, racemisation, polymerization and their racemisation, polymerization and their influence on formulation and stability of influence on formulation and stability of products. products.

Study of chemical properties of Study of chemical properties of drugs like drugs like

HydrolysisHydrolysis Oxidation – ReductionOxidation – Reduction PhotolysisPhotolysis RacemisationRacemisation Polymerization Polymerization

Mechanisms of degradation and their influence Mechanisms of degradation and their influence on formulation and stability of products on formulation and stability of products

OBJECTIVEOBJECTIVE Initial investigation Initial investigation on chemical propertieson chemical propertiesKnowledge about the Knowledge about the chemical and chemical and

physical stability physical stability of a candidate drug in the of a candidate drug in the solid and liquid state – drug developmentsolid and liquid state – drug development

Stability of formulation – Stability of formulation – shelf life shelf life of of marketed productmarketed product

Chemical properties , Chemical properties , path of degradation , path of degradation , Rate of degradation Rate of degradation

Stability with temperature ,pH, light and Stability with temperature ,pH, light and oxygen , a number of experiments need to be oxygen , a number of experiments need to be performedperformed

Hydrolysis: Hydrolysis: (drug) molecules interact with water (drug) molecules interact with water molecule to yield breakdown product.molecule to yield breakdown product.

Susceptible to the hydrolytic process: esters, Susceptible to the hydrolytic process: esters, substituted amides, lactones, and lactams.substituted amides, lactones, and lactams.

Eg: Anestheics, antibiotics , vitamins and Eg: Anestheics, antibiotics , vitamins and barbituratesbarbiturates

1. Ester hydrolysis:1. Ester hydrolysis:EsterEsterAcid + Alcohol (involves rupture of a covalent Acid + Alcohol (involves rupture of a covalent

linkage between a carbon atom and an oxygen linkage between a carbon atom and an oxygen atom).atom).

Catalysts – polar nature such as mineral acids, Catalysts – polar nature such as mineral acids, alkalies or certain enzymes – capable of supplying Halkalies or certain enzymes – capable of supplying H++ and OHand OH-- ions ions

Acid or alkali catalysed hydrolysis Acid or alkali catalysed hydrolysis

Degradation Pathway

Hydrolysis

Ester Hydrolysis

Kinetic study of hydrolysis of Aspirin was done in various buffer solutions. It was observed that Aspirin is most stable at 2.4, at pH 5 to 7 degradation is pH independent and above pH 10 stability decreases with increase in pH.

Factors to be considered in Hydrolysis pH Type of solvent : solvent lower dielectric

constant Eg.: ethanol,glycols, mannitol etc.

Complexation : steric or polar effects. Eg.: caffeine with benzocaine – electronic influence of complexing agent – alters affinity

Surfactants: nonionic , cationic , anionic stabilizes drug against base catalysis. Eg: 5% SLS – 18folds increase in t1/2 of benzocaine

Modification of chemical structure Salts and esters

Amide hydrolysisAmide hydrolysisHydrolytic reaction results : Hydrolytic reaction results :

Amide Acid +AmineAmide Acid +AmineEg.: ChloramphenicolEg.: ChloramphenicolNiacinamides Niacinamides

Ring alterations: hydrolysis proceed Ring alterations: hydrolysis proceed as a result of ring cleavage.as a result of ring cleavage.Eg. PilocarpineEg. Pilocarpine

Oxidation - reductionOxidation - reductionSecond most common way.Second most common way.

Eg.: steroids, vitamins ,antibiotics etcEg.: steroids, vitamins ,antibiotics etcMediated by free radicals or by Mediated by free radicals or by

molecular oxygenmolecular oxygenComplex oxidative processes Complex oxidative processes Sensitive towards trace metal and Sensitive towards trace metal and

other impurities other impurities Redox reactions involve either Redox reactions involve either transfer transfer

of oxygen of oxygen or or hydrogen atoms hydrogen atoms or or transfer of transfer of electrons electrons

Oxidation - reductionOxidation - reductionOxidation – presence of oxygenOxidation – presence of oxygen

Initiated by heat ,light or trace Initiated by heat ,light or trace metal ions that produce organic metal ions that produce organic free radicalsfree radicals

These radicals propagate the These radicals propagate the oxidation reaction , which proceeds oxidation reaction , which proceeds until inhibitors destroy the radicals until inhibitors destroy the radicals or until side reactions eventually or until side reactions eventually break the chainbreak the chain

Eg. DopamineEg. Dopamine

Oxidation - reductionOxidation - reductionSubstance is oxidized when :Substance is oxidized when :

If electrons are removed from itIf electrons are removed from itGains electronegative atoms or radicals or Gains electronegative atoms or radicals or

loses electropositive atoms or radicalsloses electropositive atoms or radicalsAddition of oxygen and removal of hydrogenAddition of oxygen and removal of hydrogen

Most common : autoxidation (free Most common : autoxidation (free radical chain process)radical chain process)

Involves homolytic bond fission of a Involves homolytic bond fission of a covalent bond – each atom retains one covalent bond – each atom retains one of the electrons of original covalent of the electrons of original covalent bond:bond:

AutoxidationAutoxidation Initiation: RH Initiation: RH R. + H.R. + H. Propagation: Propagation:

R. + O R. + O 2 2 RO RO 22 RO RO 22. + RH . + RH ROOH + R.ROOH + R.

Hydroperoxide decompositionHydroperoxide decomposition ROOH ROOH RO. + .OH RO. + .OH

TerminationTermination RO2. +X RO2. +X Inactive products Inactive products

(X converts to peroxides group)(X converts to peroxides group) RO2 +RO2 RO2 +RO2 Inactive productsInactive products Rate of prednisolone : presence of aerobic and Rate of prednisolone : presence of aerobic and

anaerobic conditionsanaerobic conditions Rancidity – oils and fatsRancidity – oils and fats Oxygen content and AntioxidantsOxygen content and Antioxidants

Light, heatActivation

PhotolysisPhotolysisPhotochemical Photochemical PhotosensitizerPhotosensitizerUV- violet portions – more active UV- violet portions – more active

( shortet wavelength ,more energy)( shortet wavelength ,more energy)

RacemizationRacemizationRacemization – compound changes Racemization – compound changes

optical activity without changing the optical activity without changing the chemical composition.chemical composition.

Levo and dextro formLevo and dextro formEg: l-adrenaline is 15-20times more Eg: l-adrenaline is 15-20times more

active than dextro formactive than dextro formRacemic mixtureRacemic mixture

Stability and therapeutic activityStability and therapeutic activity

Kinetics of degradation:Kinetics of degradation:K = rate of reactionK = rate of reactionDrug – ProductDrug – ProductZero ,first , second order reactions, half Zero ,first , second order reactions, half

life etc.life etc.Effect of temperature : logk = log A – Effect of temperature : logk = log A –

Ea/2.303RTEa/2.303RTDepends on functional group of Depends on functional group of

assymetrical carbon atom,aromatic grp assymetrical carbon atom,aromatic grp tends to accelerate racemizationtends to accelerate racemization

Any QuestionsAny Questions

ProdrugsProdrugs Study of prodrugs in solving problems Study of prodrugs in solving problems

related to related to Stability, Stability, Bioavailability and Bioavailability and Elegancy of formulationElegancy of formulation

Principal areas of PreformulationsPrincipal areas of Preformulations

Prodrugs- IntoductionProdrugs- Intoduction Drugs – Undesirable physicochemical and Drugs – Undesirable physicochemical and

biological propertiesbiological properties

How do one improve therapeutic efficacy?How do one improve therapeutic efficacy?Biological, Physical and Chemical meansBiological, Physical and Chemical means

Biological approach Biological approach – – Alters the ROAAlters the ROA – – may or may not be acceptable by the may or may not be acceptable by the patientpatient

Physical approachPhysical approach – – Modify the design of Modify the design of the dosage formthe dosage form Eg.: CDDS Eg.: CDDS

Chemical Approach Chemical Approach – Best to – Best to enhance the enhance the drug selectivity by minimizing the toxicity drug selectivity by minimizing the toxicity

ProdrugProdrug3 Chemical means – 3 Chemical means – To optimize the To optimize the

drug therapeuticsdrug therapeutics 1. Design and development of new 1. Design and development of new

drugs with desirable featuresdrugs with desirable featuresScreening of chemicals for Screening of chemicals for

biological activity-biological activity- Clinically useful Clinically useful 2. Design of 2. Design of hard and soft drugshard and soft drugs

with desirable characterisitcswith desirable characterisitcs 3. Design of 3. Design of prodrugsprodrugs

ProdrugProdrugHard drugs Hard drugs :Resistant to biotransformation :Resistant to biotransformation

- Long biological half life, no toxic - Long biological half life, no toxic metabolite formation. metabolite formation.

Disadv.: AccumulationDisadv.: AccumulationSoft drugs: Soft drugs: A biologically active drug

compound i.e biotransformed in vivo in a rapid and predictable manner into non- toxic moieties. Relatively inert metabolites

Disadv.: Disadv.: Short Duration Of Action Ex. Insulin, adrenaline Replacement of alkyl chain of drug – ester

group – readily hydrolysed in vivo

ProdrugProdrugA prodrug is chemically modified inert A prodrug is chemically modified inert drug precursor which upon drug precursor which upon biotransformation liberates the biotransformation liberates the pharmacologically active parent compoundpharmacologically active parent compoundPro-agent, bioreversible derivative or Pro-agent, bioreversible derivative or latentiated druglatentiated drugDesign approach – Design approach – Drug latentiationDrug latentiation

ClassificationClassificationDepends on constitution, lipophilicity and Depends on constitution, lipophilicity and method of bioactivation and catalysts involved method of bioactivation and catalysts involved in bioactivationin bioactivation

1. Carrier linked prodrugs 1. Carrier linked prodrugs 2. B2. Bioprecursorsioprecursors

Carrier linked prodrugsCarrier linked prodrugs Simple prodrugsSimple prodrugsAre ones where the active drug is Are ones where the active drug is

covalently linked to an inert carrier or covalently linked to an inert carrier or transport moietytransport moiety

Esters or amidesEsters or amidesGreatly modified lipophilicity due to the Greatly modified lipophilicity due to the

attached carrierattached carrierActive drug released by Active drug released by hydrolytic hydrolytic

cleavagecleavage either chemically or either chemically or enzymaticallyenzymatically

Carrier linked prodrugs

BioprecursorsBioprecursorsKnown as Metabolic precursorsKnown as Metabolic precursorsAre inert molecules obtained by Are inert molecules obtained by

chemical modifications of active drug chemical modifications of active drug but do not contain a carrierbut do not contain a carrier

Moiety has same lipophilicity as the Moiety has same lipophilicity as the parent drugparent drug

Bioactivated by redox Bioactivated by redox biotransformation only enzymatically biotransformation only enzymatically

Eg.: Arylacetic acid NSAID – fenbufen Eg.: Arylacetic acid NSAID – fenbufen from aroylpropionic acid precursors.from aroylpropionic acid precursors.

BioprecursorsBioprecursors

Pro-ProdrugPro-ProdrugFew cases of carrier type prodrugs to be fFew cases of carrier type prodrugs to be formulated ormulated as ophthalmic, parenteral or oral liquid as ophthalmic, parenteral or oral liquid preparations, the conversion to active drug –- preparations, the conversion to active drug –- Chemically ( non enzymatically) triggered by Chemically ( non enzymatically) triggered by change in pH –- Stability problemschange in pH –- Stability problems

Overcome by :Overcome by :Double prodrug or pro-prodrug conceptDouble prodrug or pro-prodrug conceptFurther derivatized in a fashion – Only Further derivatized in a fashion – Only

enzymatically conversion of prodrug is enzymatically conversion of prodrug is possible before the latter can cleave to possible before the latter can cleave to release the active drugrelease the active drug

Eg.: diesters of pilocarpic acidEg.: diesters of pilocarpic acid

Mutual ProdrugMutual Prodrug In contrast to simple prodrugs where the In contrast to simple prodrugs where the

carrier used is biologically inert,carrier used is biologically inert,Prodrug comprises of 2 pharmacological Prodrug comprises of 2 pharmacological

active agents coupled together to form a active agents coupled together to form a single molecule that each acts as carrier single molecule that each acts as carrier for the otherfor the other

Prodrugs of two active compounds are Prodrugs of two active compounds are called as mutual prodrugscalled as mutual prodrugsEg.: Benorylate : For NSAID’s of aspirin Eg.: Benorylate : For NSAID’s of aspirin

and paracetamoland paracetamol

Examples of ProdrugExamples of ProdrugAspirin – Produg of salicylic acid- Aspirin – Produg of salicylic acid-

decrease GI irritationdecrease GI irritationHexamine – Excreted in urine is Hexamine – Excreted in urine is

converted to formaldehyde in converted to formaldehyde in the acidic urine pH - Urinary tract the acidic urine pH - Urinary tract antibacterialantibacterial

Ideal characteristics of ProdrugIdeal characteristics of Prodrug Shouldn’t have intrinsic Shouldn’t have intrinsic

pharmacological activity- pharmacological activity- InertInert Rapidly transformRapidly transform, chemically or , chemically or

enzymatically into the active form enzymatically into the active form where desiredwhere desired

The metabolic fragments, apart The metabolic fragments, apart from the active drug should be from the active drug should be nontoxicnontoxic

Applications - ProdrugApplications - Prodrug Pharmaceutical Applications:Pharmaceutical Applications:

Improvement of tasteImprovement of tasteImprovement of odorImprovement of odorChange of physical form for preparation Change of physical form for preparation

of solid dosage formsof solid dosage formsReduction of GI irritationReduction of GI irritationReduction of pain on injectionReduction of pain on injectionEnhancement of drug solubility and Enhancement of drug solubility and

dissolution ratedissolution rateEnhancement of chemical stability of Enhancement of chemical stability of

drugdrug

Applications - ProdrugApplications - ProdrugPharmacokinetic ApplicationsPharmacokinetic Applications

Enhancement of bioavailability Enhancement of bioavailability (lipophilicity)(lipophilicity)

Prevention of pre-systemic Prevention of pre-systemic metabolismmetabolism

Prolongation of duration of actionProlongation of duration of actionReduction of toxicityReduction of toxicitySite specific drug delivery (drug Site specific drug delivery (drug

targeting)targeting)

Any QuestionsAny Questions

Improvement of tasteImprovement of taste Poor patient compliancesPoor patient compliances

Bitterness, acidity etcBitterness, acidity etc Two approaches :Overcome tasteTwo approaches :Overcome taste

Reduction of drug solubility in saliva Reduction of drug solubility in saliva To lower the affinity of drug towards taste To lower the affinity of drug towards taste

receptorsreceptorsEg.: Chloramphenicol – Palminate ester Eg.: Chloramphenicol – Palminate ester Clindamycin – Palminate esterClindamycin – Palminate ester

Principal areas of PreformulationsPrincipal areas of Preformulations

Improvement of Improvement of odorodor

Depends upon its vapor pressure (BP)Depends upon its vapor pressure (BP)High v.p has low b.p = Strong odorHigh v.p has low b.p = Strong odor

Eg.: Ethyl mercaptan – foul smell at Eg.: Ethyl mercaptan – foul smell at b.p 35°Cb.p 35°C

Used in treatment of leprosy,is Used in treatment of leprosy,is converted to phthalate ester converted to phthalate ester (diethyldithio-isophthalate) higher (diethyldithio-isophthalate) higher b.p and is odorlessb.p and is odorless

Change of Physical form of the Change of Physical form of the drugdrug

Liquid form – unsuitable for Liquid form – unsuitable for formulation as tablet if dose is highformulation as tablet if dose is high

Conversion of such liquid drug into Conversion of such liquid drug into solid prodrugs - formation of solid prodrugs - formation of symmetrical molecules – Higher symmetrical molecules – Higher tendency to crystallizetendency to crystallize

Eg. Trichloroethanol converted to Eg. Trichloroethanol converted to p-acetamidobenzoic acid esterp-acetamidobenzoic acid ester

Reduction of GI irritationReduction of GI irritation Irritation and damage to gastric mucosaIrritation and damage to gastric mucosa

Direct contactDirect contactIncreased stimulation of acid Increased stimulation of acid

secretionsecretionThrough interference with the Through interference with the

protective mucosal layerprotective mucosal layerEg.: NSAID’s ,especially salicylates Eg.: NSAID’s ,especially salicylates

Lowers the gastric pH and induces Lowers the gastric pH and induces or aggravates ulcerationor aggravates ulceration

Eg: Salicylic acid – AspirinEg: Salicylic acid – Aspirin

Reduction of pain or Reduction of pain or injectioninjection

IM injection – Painful when drug IM injection – Painful when drug precipitates or penetrates into the precipitates or penetrates into the surrounding cells or when the solution surrounding cells or when the solution is strongly acidic , alkaline or alcoholic is strongly acidic , alkaline or alcoholic

Eg.1: Eg.1: Low aq. solubilityLow aq. solubility of clindamycin of clindamycin HClHCl

Overcome by more Overcome by more water soluble water soluble prodrugprodrug such as 2 such as 2`̀-phosphate ester of -phosphate ester of clindamycinclindamycin

Enhancement of solubility and Enhancement of solubility and dissolution rate dissolution rate

Hydrophilicity of drug:Hydrophilicity of drug:When dissolution is rate limiting step in When dissolution is rate limiting step in

absorption of poorly aq.soluble agents or when absorption of poorly aq.soluble agents or when parenteral or ophthalmic formulations parenteral or ophthalmic formulations Hydrophilic or water soluble drug are desiredHydrophilic or water soluble drug are desired

Eg: Drugs – OH group can be converted into Eg: Drugs – OH group can be converted into their hydrophilic forms by use of half esters their hydrophilic forms by use of half esters such as hemisuccinates, hemi glutarates etcsuch as hemisuccinates, hemi glutarates etc

Other half of these acidic carriers can form Na, Other half of these acidic carriers can form Na, K or amine salts – renders the moiety water K or amine salts – renders the moiety water solublesoluble

Enhancement of solubility and Enhancement of solubility and dissolution ratedissolution rate

For alcoholic or phenolic drugs : For alcoholic or phenolic drugs : Steroidal drugs like cortisol. Steroidal drugs like cortisol. prednisolone , dexamethsone, the prednisolone , dexamethsone, the sodium succinate salts have poor sodium succinate salts have poor stability and hence phosphate esters are stability and hence phosphate esters are preferredpreferred

Eg1: Chloramphenicol – Sodium Eg1: Chloramphenicol – Sodium succinate estersuccinate ester

Eg2: Tetracycline – TetralysineEg2: Tetracycline – TetralysineEg3: Diazepam – L- lysine esterEg3: Diazepam – L- lysine ester

Enhancement of chemical stability Enhancement of chemical stability A drug may destabilize - shelf life or GIT OrallyA drug may destabilize - shelf life or GIT Orally Shelf life stability- IVShelf life stability- IV Conventional approach – Conventional approach – LyophilizeLyophilize such such

solutions into powder which is reconstituted solutions into powder which is reconstituted before usebefore use

Improves stabilityImproves stability Antineoplastic drug: azacytidine Antineoplastic drug: azacytidine

Aq.solution – hydrolyzed but bisulfite prodrug Aq.solution – hydrolyzed but bisulfite prodrug is stable to degradation at acidic pH and is stable to degradation at acidic pH and more water soluble than the parent drugmore water soluble than the parent drug

Conversion at physiologic pH 7.4Conversion at physiologic pH 7.4 Cefamandole – nafate ester prodrug – improved Cefamandole – nafate ester prodrug – improved

shelf life( Reconstitution from dry powder)shelf life( Reconstitution from dry powder)

Prodrug stabilityProdrug stability Pencillins – More susceptible to hydrolysis Pencillins – More susceptible to hydrolysis

and destabilization in gastric acidand destabilization in gastric acid Carbenicillin – cannot be administered Carbenicillin – cannot be administered

orallyorally Its ester prodrug carindacillin (Its ester prodrug carindacillin (αα indanol ester) indanol ester)

and carfecillin (and carfecillin (αα phenyl ester – more stable phenyl ester – more stableAt pH 7.0 hydrolysis releases the active drug At pH 7.0 hydrolysis releases the active drug

and absorbedand absorbedErythromycin – stearate( ethyl succinate and Erythromycin – stearate( ethyl succinate and

estolate )estolate )

Any QuestionsAny Questions

Enhancement of Bioavailability Enhancement of Bioavailability Most drugs – Passive diffusion – lipophilicity Most drugs – Passive diffusion – lipophilicity 2reasons to enhance oral bioavailability of 2reasons to enhance oral bioavailability of

lipophilic compoundslipophilic compoundsLipophilic forms – Enhanced membrane/water Lipophilic forms – Enhanced membrane/water

partition co-efficient compared with hydrophilic partition co-efficient compared with hydrophilic formformEg.: pivampicillin ,talampicillin prodrugs of Eg.: pivampicillin ,talampicillin prodrugs of

ampicillin are lipophilic (98%) and rapidly ampicillin are lipophilic (98%) and rapidly hydrolysed to parent drug in bloodhydrolysed to parent drug in blood

Esters of erythromycinEsters of erythromycin

Principal areas of PreformulationsPrincipal areas of Preformulations

Enhancement of Enhancement of BioavailabilityBioavailability

The dipalmitoyl gylcerol ester of NSAID The dipalmitoyl gylcerol ester of NSAID naproxen – less GI and high plasma conc.naproxen – less GI and high plasma conc.

Intraocular penetration of polar drugs – Intraocular penetration of polar drugs – ββ blockers and epinephrine – treatment of blockers and epinephrine – treatment of glaucoma – use lipophilic carrier glaucoma – use lipophilic carrier

Eg.: diacetate ester of nadolol is 20 times more Eg.: diacetate ester of nadolol is 20 times more lipophilic and 10 times more readily absorbed lipophilic and 10 times more readily absorbed ocularlyocularly

The dipivalyl ester of epinephrine – good ocular The dipivalyl ester of epinephrine – good ocular penetrability (8-17times) in comparison to the penetrability (8-17times) in comparison to the parent drugparent drug

Enhancement of Enhancement of BioavailabilityBioavailability

Increased bioavailability through increased Increased bioavailability through increased lipophilicity – Is reduction in drug dosagelipophilicity – Is reduction in drug dosageEg.: bacampicillin – prodrug for ampicillin (1/3Eg.: bacampicillin – prodrug for ampicillin (1/3rdrd

the dose)the dose)Bioavailability of topically applied drug – depends Bioavailability of topically applied drug – depends

on lipid solubilityon lipid solubilitySkin penetrability of polar drugs can be improved Skin penetrability of polar drugs can be improved

by esterification to form lipid soluble compoundby esterification to form lipid soluble compoundDrugs with carboxyl functions is their Drugs with carboxyl functions is their

esterfication with one of the hydroxyl groups of esterfication with one of the hydroxyl groups of PG or glycerolPG or glycerol

Penetration enhancer – PG or glycerolPenetration enhancer – PG or glycerolEg: glyceryl ester of naproxenEg: glyceryl ester of naproxen

First Pass MetabolismFirst Pass MetabolismCorticosteroids – extensive FPMCorticosteroids – extensive FPM

Use their ester or ether prodrugsUse their ester or ether prodrugsEg.: triamcinolone acetonideEg.: triamcinolone acetonide

Propanolol – its hemisuccinate Propanolol – its hemisuccinate prodrug resistant to esterases of liverprodrug resistant to esterases of liver

Duration Of ActionDuration Of Action Prolonged DOA:Prolonged DOA:

Shorter half life: Frequent dosing requiredShorter half life: Frequent dosing required Overcome by use of both controlled release and Overcome by use of both controlled release and

prodrug approchesprodrug approches Rate of release of prodrug – Controlled releaseRate of release of prodrug – Controlled release Conversion of prodrug to drug- Controlled releaseConversion of prodrug to drug- Controlled release Eg: IM depot inj. Of lipophilic ester prodrugs of Eg: IM depot inj. Of lipophilic ester prodrugs of

steroids (testosterone cypionate and steroids (testosterone cypionate and propionate,estradiol propionate)propionate,estradiol propionate)

Antipsychotics (fluphenazine enanthate and Antipsychotics (fluphenazine enanthate and decanoate)decanoate)

Pilocarpine – glaucoma( diesters of the drug)Pilocarpine – glaucoma( diesters of the drug)

Reduction of toxicityReduction of toxicity Objective of drug design : high activity with low Objective of drug design : high activity with low

toxicitytoxicity Eg.: timolol and epinephrine Eg.: timolol and epinephrine

High dose – Poor penetration , CV side effectsHigh dose – Poor penetration , CV side effectsLipophilic esters – Better intraocular penetration Lipophilic esters – Better intraocular penetration

and reduces the instilled doses – reduces and reduces the instilled doses – reduces adverse effects adverse effects

Eg.: TI of alkyl ester prodrug of timolol – Eg.: TI of alkyl ester prodrug of timolol – improved 16times while that of dipivalyl improved 16times while that of dipivalyl epinephrine or dipivefrin (a diester of epinephrine or dipivefrin (a diester of epinephrine with pivalic acid) increased 10timesepinephrine with pivalic acid) increased 10times

Improved biochemical(decreased metabolic rate Improved biochemical(decreased metabolic rate in ocular tissues) and chemical stability in ocular tissues) and chemical stability (resistance to oxidation)(resistance to oxidation)

Site Specific Drug DeliverySite Specific Drug Delivery Selective Uptake systemsSelective Uptake systems Redox system for drug delivery to brainRedox system for drug delivery to brain Site specific drug delivery in cancerSite specific drug delivery in cancer Limitations of prodrug design :Limitations of prodrug design :

Toxicity – may be due to Toxicity – may be due to Formation of an unexpected metabolite from total Formation of an unexpected metabolite from total

prodrug that may be toxicprodrug that may be toxic Inert carrier generated following cleavage of Inert carrier generated following cleavage of

prodrug may also transform into a toxic prodrug may also transform into a toxic metabolitemetabolite

During activation, consumption of vital cell During activation, consumption of vital cell constitutent such as glutathione leading to its constitutent such as glutathione leading to its depletion depletion

Eg.: Prodrug Phenacetin – paracetamol – de-Eg.: Prodrug Phenacetin – paracetamol – de-ethylation. Other intermediates like p-phenetidine ethylation. Other intermediates like p-phenetidine and n hydroxy phenacetin is also formedand n hydroxy phenacetin is also formed

p-phenetidine – further metabolizes to ppt p-phenetidine – further metabolizes to ppt methemoglobinemia,hemolysis and renal toxicitymethemoglobinemia,hemolysis and renal toxicity

REFERENCESREFERENCESThe Theory and Practice of Industrial The Theory and Practice of Industrial

Pharmacy Pharmacy By Leon Lachman, H.A Lieberman, By Leon Lachman, H.A Lieberman,

Joseph Kanig, 3Joseph Kanig, 3rdrd edition ,page: 184-195 edition ,page: 184-195

REFERENCESREFERENCESThe Theory and Practice of Industrial The Theory and Practice of Industrial

Pharmacy Pharmacy By Leon Lachman, H.A Lieberman, Joseph By Leon Lachman, H.A Lieberman, Joseph

Kanig, 3Kanig, 3rdrd edition ,page: 171-176 edition ,page: 171-176www.pharmacy.utah.edu/pharmaceutics/p

df/Preformulation.pdf

ReferencesReferencesBiopharmaceutics and Pharmacokinetics Biopharmaceutics and Pharmacokinetics

A treatise – By D.M Brahmankar and Sunil A treatise – By D.M Brahmankar and Sunil B.Jaiswal,Page :159-177B.Jaiswal,Page :159-177

References References

Lachman , Page: 772-786Lachman , Page: 772-786