(ANTIBIOTICS)

MWEETWA L: Pharmacologist

University of Zambia & Lusaka Apex Medical University

Pharmacy Faculty

CHEMOTHERAPEUTIC DRUGS

Learning objectives

• Understand Guiding Principles of antimicrobial therapy

• Understand Bacteria Structure

• Understand Classification and Mechanisms of Action of Antimicrobial agents and other chemotherapeutic drugs

• Understand Factors influencing Drug Resistance

Introduction to principles of chemotherapy

I. DEFINITIONS

II. HISTORY

III. MECHANISMS OF ANTIMICROBIAL AGENTS

IV. MECHANISMS OF ANTIBACTERIAL RESISTANCE

V. GENERAL PRINCIPLES OF ANTI-INFECTIVE

THERAPY

VI. IDEAL ANTIMICROBIAL DRUG

Principles of Chemotherapy

• Antimicrobial therapy takes advantage of :-• 1.Biochemical differences that exist between

microorganisms and human beings.

• 2. Antimicrobial drugs are effective in the treatment of infections because of their selective toxicity; that is, they have the ability to injure or kill an invading microorgan-ism without harming the cells of the host.

• 3. In most instances, the selective toxicity is relative rather than absolute, requiring that the concentration of the drug be carefully controlled to attack the microorganism, while still being tolerated by the host.

SELECTION OF ANTIMICROBIAL AGENTS

• Selection of the most appropriate antimicrobial agent requires knowing

• 1) the organism’s identity - gram -/+

• 2) the organism’s susceptibility to a particular • agent,

• 3) the site of the infection - blood-brain barrier effects, Protein binding, lipid solubility and MW of the drug

• 4) patient factors-Renal/Hepatic nature,age,sex,pregnacy,lactation and immune system

• 5) the safety of the agent, e.g chlorampheniciol and aminoglycosides and

• 6) the cost of therapy. However, some patients require empiric therapy.

SELECTION OF ANTIMICROBIAL AGENTS

• INFLUENCE OF ROUTE OF ADMINISTRATION

• The oral route of administration is chosen for infections that are mild and is favorable for treatment on an outpatient basis.

• However, some antibiotics, such as vancomycin, the aminoglyco-sides, and amphotericin B, are so poorly absorbed from GIT

SELECTION OF ANTIMICROBIAL AGENTS

• INFLUENCE OF RATIONAL DOSING

• Rational dosing of antimicrobial agents is based on their pharmacodynamics AND phar-macokinetic properties

• Three important properties that have a significant body influence on the frequency of dosing are

• 1. concentration-dependent killing, • 2. time-dependent killing, and • 3.postantibiotic effect.

• Utilizing these properties to optimize antibiotic dosing regimens can improve clinical out-comes and possibly decrease the development of resistance.

Understanding Bacteria structure

• Most pathological bacterial species are referred to by genus name only e.gklebsilla,Pseudomonas,proteus etc

• Some are referred by species name e.g E.Coli

TAXONOMY OF BACTERIA

TAXONOMY OF BACTERIA

GRAM STAIN

Gram-negative bacteria are a class of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation

coccobacilli

Practical classification of bacteria

Bacterial Etiologies

Common Normal flora bacteria

BACTERIA INFECTION SITES

COMMON Etiologic Bacteria

introduction

Chemotherapy is the drug treatment for the diseases caused by pathologic microorganisms, parasites, and tumour cells.

The objective of chemotherapy is to study and to apply the drugs that have highly selective toxicity to the pathogenic microorganisms and have no or less toxicity to the host.

WHAT IS AN ANTIBIOTIC?

“Antibiotic” is from antibiosis, meaning• against life.

Substances produced by various species• of microorganisms: bacteria, fungi,• actinomycetes— to kill or suppress the• growth of other microorganisms.

Today the term antibiotic extends to include• synthetic antibacterial agents: sulfonamides and

quinolones.

ANTIMICROBIAL SPECTRUM

• Antimicrobial spectrum : the scope that• a drug kills or suppresses the growth of• microorganisms.

• Narrow-spectrum: The drugs that only act• on one kind or one strain of bacteria.• (isoniazid )

• Broad-spectrum: The drugs that have a• wide antimicrobial scope. (tetracycline,• chloramphenicol )

The minimal inhibitory concentration (MIC)

• The minimal inhibitory concentration (MIC)• the minimum amount of a drug required to inhibit the growth of

bacteria in vitro.

• • The minimal bactericidal concentration (MBC)• the minimum amount of a drug required to kill bacteria in vitro.

• TYPES• Natural Antibiotics Antimicrobial drugs produced by

microorganisms.

• Synthetic Antibiotics Antimicrobial drugs• synthesized in the lab.

II.HISTORY

1929 Penicillin discovered by Alexander Fleming

Messy lab, cool damp weather, luck

1940 Florey and Chain mass produce penicillin for war time use, becomes available to the public.

1935 Sulfa drugs discovered

1943 Streptomycin discovered

Western civilization fundamentally changed

MECHANISMS OF ANTIMICROBIAL AGENTS

1. INHIBITION OF CELL WALL SYNTHESIS

2. INHIBITION OF FUNCTIONS OF CELLULAR MEMBRANE

3. INHIBITION OF PROTEIN SYNTHESIS

4. INHIBITION OF NUCLEIC ACID SYNTHESIS

5. INHIBITION OF FOLIC ACID SYNTHESIS

CON ...

Inhibition of cell wall synthesis

• Penicillins and cephalosporins stop synthesis

• of wall by preventing cross linking of

• peptidoglycan units.

• – Bacitracin and vancomycin also interfere

• here.

• – Excellent selective toxicity

2. Inhibition of functions of cellular membrane:

• – The bacterial cell membrane is also called

cytoplasmic membrane. Its main compounds

are proteins and lipids.

• – Polymyxins can selectively combine with

phosphatide in the cell membrane and cause

the increase of membranous permeability. As the result, some important materials will outflow from bacterial cells and result in death of bacteria.

3. Inhibition of protein synthesis

• – Due to differences in ribosomes

Eucaryotic cells have 80S (60S + 40S subunits)

ribosomes.

Procaryotic cells have 70S (50S + 30S subunits)

ribosomes.

• – Examples:

• • Chloramphenicol,Macrolides and Clindamycin

bind to the 50S subunit.

• • Tetracyclines and Aminoglycosides bind to

the 30S subunit.

Inhibition of nucleic acid synthesis

• – Stop DNA replication

• • Example: Quinolones-inhibiting DNA

gyrase; Metronidazole???-DNA

Polymerase

Or stop RNA synthesis

• • Example: Rifampin -binds to the bacterial

• DNA-dependent RNA polymerase

5. Inhibition of folic acid synthesis

A drug mimics a normal metabolite andacts as a competitive inhibitor.

– Enzyme of cell recognizes the drug instead ofthe normal metabolite-Pathway stops.

– Example: Sulfonamides and trimethoprim are similar to PABA (para aminobenzoic acid).inhibit folic acid synthesis by blockingdihydrofolic acid synthase and reductaserespectively.

IV.RESISTANCE TO ANTIBACTERIAL AGENTS

• Drug resistance is the phenomenon thatsusceptibility of pathogenic microorganismsto drugs becomes lower or even loses afterthe microorganisms contact with drugs manytimes.

• When the bacteria show resistance to onedrug, they are also resistant to some otherdrugs. This phenomenon is called crossdrug resistance.

TYPES OF RESISTANCE

• Intrinsic or natural resistance• e.g., no target site in the bacteria

• Acquired resistance–Resistance acquired by mutation is unusual,–Resistance acquired by R-factors on plasmids is common, very rapid method of acquiringresistance that often involves resistance tomany antibiotics. (R factor contains genescoding for enzymes that make the cell resistant to antibiotics)

ANTIBIOTIC Resistance

• 1.Alteration of the target site of the antibiotic?• One of the most problematic antibiotic resistances worldwide, • methicillin resistance among Staphylococcus aureus.

• 2.Enzyme inactivation of the antibiotic?• β-lactam antibiotics (penicillins & cephalosporins) can be • inactivated by β-lactamases.

• 3. Active transport of the antibiotic out of the bacterial cell • Active transport of the antibiotic out of the bacterial cell • (efflux pumps) ? • Removal of some antibiotics (i.e. tetracyclines, macrolides, & • quinolones)

• 4.Decreased permeability of the bacterial cell wall to the • antibiotic? • Alteration in the porin proteins that form channels in the cell membrane e.g Resistance of

Pseudomonas aeruginosa to a variety of penicillins and cephalosporins

ANTIBIOTIC Resistance

Antibiotic resistance animation

1. Mechanisms of antibacterial resistance

• Antibiotic inactivation– bacteria acquire genes encodingenzymes that inactivate antibiotics

• Examples include:– b-lactamases– aminoglycoside-modifying enzymes– chloramphenicol acetyl transferase

2. Mechanisms of antibacterial resistance

Altered uptake of antibiotics, resulting in:– decreased permeability

– increased efflux

– For example, gram-negative bacillus caninduce some special proteins to block porinchannels in cell wall and prevent tetracyclinesinto the bacillus.

3. Mechanisms of antibacterial resistance Structurally modified antibiotic target site

– For example, as the receptor protein on the 30s ribosomal subunit may be deleted or altered as a result of mutation, some aminoglycosides cannot combine with the bacteria.

4.Mechanisms of antibacterial resistance

Develop an altered metabolic pathway– Bacteria can develop an altered metabolicpathway that bypasses the reaction inhibitedby drugs.– For example, sulfonamide resistance myoccur as a result of mutations that causeover-production of PABA or cause productionof a folic acid-synthesizing enzyme that haslow affinity for sulfonamides.Mechanisms of antibacterial resistancePABA, p-aminobenzoic acid

GENERAL PRINCIPLES OF ANTI-INFECTIVE THERAPY

• ① Identification of the infecting organism should

• precede antimicrobial therapy when possible.

• ② The pathogenic microorganism susceptibility to antimicrobial agents should be determined, if a suitable test exists.

• ③ Factors that influence the choice of an antiinfective agent or its dosage for a patient

include the age, renal and hepatic function,

pregnancy status, and the site of infection, etc.

Selection of Antimicrobial Agent

• Empiric therapy - prior to identification of organism – critically ill patients

• Organism’s susceptibility to the antibiotic• Patient factors - immune system, renal/hepatic function• Effect of site of infection on therapy –blood brain barrier• Safety of the agent• Cost of therapy

IDEAL ANTIMICROBIAL DRUG

Have highly selective toxicity to the pathogenic

microorganisms in host body

Have no or less toxicity to the host.

Low propensity for development of resistance.

Not induce hypersensitive reactions in the host.

Have rapid and extensive tissue distribution

Be free of interactions with other drugs.

Be relatively inexpensive

Properties Influencing Frequency of Dosing

• Post-antibiotic effect (PAE)– persistent suppression of microbial growth after levels

of antibiotic have fallen below MIC

Antibiotics with a long PAE – aminoglycosides

and fluroquinolines

Minimum bacterial concentration (MBC) is

the lowest concentration of antibiotic that

kills 99.9% of bacteria

MIC

Chemotherapeutic Spectra

• Narrow-spectrum Antibiotics: • Act on a single / limited group of micro-organisms; • e.g., isoniazid given for mycobacterium

• Extended-spectrum Antibiotics: • Effective against gram-positive organisms and a • significant number of gram-negative organisms; e.g., • Ampicillin

• Broad-spectrum Antibiotics: • Effective against a wide variety of microbial species; • e.g., tetracycline & chloramphenicol. • Can alter the nature of intestinal flora = super infection

Combinations of Antimicrobial Drugs

• Advantages• Synergism; the combination is more effective than either drug used separately; β-lactams and Aminoglycosides

• Used for Infections of unknown originDisadvantagesBacteriostatic (tetracycline) drugs may interfere with bactericidal ( penicillin and cephalosporin) drugs

Complications of Antibiotic Therapy

• Resistance – inappropriate use of antibiotics

• Hypersensitivity – penicillin

• Direct toxicity – aminoglycosides = ototoxicity

• Super infections – broad spectrum

antimicrobials cause alteration of the normal

flora; often difficult to treat

MECHANISMS OF ANTIBIOTICS

MECHANISMS OF ANTIBIOTICS

β-LACTAM ANTIOBIOTICS

CELL WALL INHIBITORS

• Interfere with the synthesis of the bacterial cell wall

• Little or no effect on bacteria that are not growing and dividing

Cell wall inhibitors

PENICILLINS (bactericidal)

• Most widely effective and least toxic

• Limited use - increased resistance

Mechanism of action

• Inactivates various proteins on bacterial

cell wall

Administration and Fate of PENICILLIN

• Does not penetrate CNS unless meninges are inflamed

• Routes of Administration• • Oral only –Pen V, Amoxicillin & • amoxicillin combined with clavulanic• acid• IV / IM- Tiracillin, piperacillin, ampicillin with sulbactam, tiracillin with clavulanic acid

and piperacillin with tozobactam

• Absorption• • Decreases by food in the stomach –administer before meals 30-60minDistribution to bone and CSF • insufficientExcretion - Kidneys

Adverse Effects of Penicillin

CEPHALOSPORINS (bactericidal)

• Semi-synthetic antibioticsβ-lactam antibiotics are closely related functionally

and structurally to penicillins

• Mode of action - inhibit the synthesis of the cell wall• More resistant than penicillins to certain β –lactamases• Classified as 1st, 2nd, 3rd, 4 and 5th generation –

based on spectrum of antimicrobial activity

CEPHALOSPORINS classification

Most Common Side Effects –

• • Diarrhoea• • Nausea• • Abdominal pain• • Vomiting• • Headache

Individuals hypersensitive to penicillins may also be hypersensitive to

Cephalosporins

• • Dizziness• • Skin rash• • Fever• • Abnormal liver tests• • Vaginitis

• • Like almost all antibiotics, may cause mild

or severe cases of seudomembranous

colitis

OTHER β-LACTAM ANTIOBIOTICS

OTHER β-LACTAM ANTIOBIOTICS

• Carbapenems:

Imipenem – broad spectrum of activity

against Gram +ve and Gram –ve aerobic

and anaerobic bacteria

• Meropenem – Important for empirical

mono therapy of serious infections

OTHER β-LACTAM ANTIOBIOTICS

• Monobactams• Activity is restricted to Gram –ve aerobic bacteria e.g Aztreonamβ-lactamase inhibitors clavulanic acid –sulbactam and tazobactamDo not have significant antibacterial activityBind to and inactivate the β-lactamases –protect the Antibiotics henceFormulated in combination with β-lactamase sensitive antibioticsClavulanic acid and amoxicillin

VANCOMYCIN

• Tricyclicglycopeptide• • Effective against multiple drug resistant

organisms

• (MRSA) & enterococci• • Resistance is becoming a Problem• Enterococcus faecium• Enterococcusfaecalis• Side Effects: chills,Fever,Flushing,Phlebitis

DAPTOMYCIN

• Cyclic lipopeptide – linezolid and quinupristin / • dalfopristin

• Treatment of infections caused by resistant gram +ve• MRSA – methicillin S. Aureus• MSSA - methillin susceptible S. Aureus• VRE - vancomycin- resistant enterococci• Daptomycin is bactericidal and Concentration dependent• Inactivated by surfactant – never used in • treatment of pneumonia

TELAVANCIN

• Semi-synthetic lipoglycopeptide antibiotic

• Synthetic derivative of Vancomycin

• Used in Treatment of complicated skin and

skin structure infections caused by resistant gram +ve organisms including MRSA

Mechanism of Action

• • Inhibits bacterial cell wall synthesis

• • Also involves disruption of bacterial cell membrane• • Bactericidal against MRSA• Side effects• Metallic Taste, foamy urine• Not recommended in pregnancy • QT Prolongation, insomnia• Headache

PROTEIN SYNTHESIS INHIBITORS

TETRACYCLINES

• Broad-spectrum bacteriostatic antibiotic

• Effective against:

• Gram+ve and Gram-ve bacteria and

• Organisms other than bacteria

TETRACYCLINES

TETRACYCLINES

TETRACYCLINES

TETRACYCLINE SIDE EFFECTS

GLYCYLCYCLINES

• (Pronunciation: gli-sil-sī-klēns)• Tigecycline – a derivative of minocycline• Similar to tetracycline• Broad-spectrum activity against Multidrug-

resistant Gram +ve pathogens Some Gram –veorganisms Aerobic organisms

• Treatment of complicated skin and soft tissue infections and complicated intra-abdominal • infectionsMechanism of action – Binds to 30s Ribosome sub

unit with bacteriostatic action

GLYCYLCYCLINES Adverse Effects

• Associated with nausea and vomiting and

• other adverse effects similar to tetracyclines

• Drug interactions

• Inhibits the clearance of warfarin

• Oral contraception with Glycylcyclines –

• less effective

AMINOGLYCOSIDES

• Similar antimicrobial spectrum to Macrolides

• Relatively toxic but still useful in treatment of infections caused by anaerobic Gram –ve bacteria

• Ototoxicity = main limitation

• Inhibit bacterial protein synthesis by acting on the 30S ribosome subunit

• Good to know: Only available IV

• Not absorbed by gut

AMINOGLYCOSIDES spectrum

• Antibacterial spectrum – effective in

combination for empirical treatment of

aerobic Gram –ve bacilli infections –

• Pseudomonas

• Combines with a β-lactam i.e.

• Vancomycin Aminoglycosides and

• bactericidal amikacin,gentamycin,

• tobramycin and streptomycin

AMINOGLYCOSIDES mechanism of action

• Interferes with bacterial protein synthesis by binding to the 30S ribosomal subunit. An oxygen-dependent transport system is necessary for aminoglycosides to reach their target site; the transport system is inhibited by divalent cations (Ca++, Mg++), low pH, anaerobiasis, and hyperosmolarity.

• Rapidly bactericidal.• Concentration-dependent bactericidal activity, which means that the rate

and extent of bacterial killing increases as drug concentrations increase.

• Post-antibiotic effect (ie): continued killing of bacteria despite antibiotic levels below the MIC of the organism.

• These pharmacodynamic properties (concentration-dependent killing and post-antibiotic effect is the rationale for once daily dosing of aminoglycosides.

aminoglycoside modifying enzymes

• aminoglycoside modifying enzymes that inactivate the aminoglycoside via

• adenyltransferase --> adenylation of a hydroxyl group

• acetyltramsferase --> acetylation of an amino group• phosphotransferase --> phosphorylation of a

hydroxyl group• Amikacin is less susceptible to aminoglycoside-

modifying enzymes because of protective side chains, and therefore may still be useful when resistance to gentamicin or tobramycin develops.

AMINOGLYCOSIDES SIDE EFFECTS

MACROLIDES

MACROLIDES Mode of action

• Macrolides are protein synthesis inhibitors. • They inhibit bacterial protein biosynthesis, and

are thought to do this by preventing peptidyltransferase from adding the growing peptide attached to tRNA to the next amino acid

• Leading to premature dissociation of the peptidyl-tRNA from the ribosome.

• Macrolide antibiotics do so by binding reversibly to the P site on the subunit 50S of the bacterial ribosome

MACROLIDES indications

MACROLIDES PHARMACOCKINETICS

MACROLIDES SIDE EFFECTS

Chloramphenicol

• Active against a wide range of

• Gram +ve and Gram –ve organisms

• High toxicity – bone marrow toxicity

• Restricted for life-threatening infections where no alternative exists

CHLORAMPHENICOL SIDE EFFECTS

CLINDAMYCIN

• Mechanism of action same as

• Erythromycin

• Treatment of infections caused by

• anaerobic bacteria – Bacteriodes

• fragilis (infections associated with

• trauma) & MRSA

• Resistance same as erythromycin

Quinupristin / Dalfopristin

• They belong to streptogramins antibiotics

• Quinupristin and dalfopristin are protein synthesis inhibitors in a synergistic manner. While each of the two is only a bacteriostatic agent, the combination shows bactericidal activity.

• Dalfopristin binds to the 23S portion of the 50s ribosomal subunit, and changes the conformation of it, enhancing the binding of quinupristin by a factor of about 100. In addition, it inhibits peptidyl transfer

• Quinupristin binds to a nearby site on the 50S ribosomal subunit and prevents elongation of the polypeptide as well as causing incomplete chains to be released.

LINEZOLID

• It selectively inhibits bacterial protein synthesis

• Binds to bacterial ribosome and prevents the formation of a functional 70S-initiation complex.

• Specifically, linezolid binds to a site on the bacterial 23S ribosomal RNA of the 50S subunit and prevents the formation of a functional 70S initiation complex, which is an essential component of the bacterial translation process

LINEZOLID

NUCLEIC ACID INHIBITORS -FluroqUINOLONES

QUINOLONES MODE OF ACTION

• They inhibit the enzymes topoisomerase II (DNA gyrase) and topoisomerase IV, which are required for bacterial DNA replication, transcription, repair, strand supercoilingrepair, and recombination.

• Indications urinary tract infections, acute uncomplicated cystitis, chronic bacterial prostatitis, lower respiratory tract infections, acute sinusitis, skin and skin structure infections, bone and joint infections, complicated intra-abdominal infections (used in

combination with metronidazole), infectious diarrhea, typhoid fever (enteric fever), and inhalational anthrax (post-exposure).

Therapeutic Applications of Fluroquinolones

Adverse Reactions to FlUroquinolones

Sulphonamides

• Short-acting•

• Sulfacetamide• Sulfadiazine• Sulfadimidine• Sulfafurazole• Sulfisomidine (also known as sulfaisodimidine)•

• Intermediate-acting• Sulfadoxine• Sulfamethoxazole• Sulfamoxole• Long-acting• Sulfadimethoxine• Sulfamethoxypyridazine• Sulfametoxydiazine• Ultra long-acting• Sulfadoxine• Sulfametopyrazine

SULFONAMIDE MODE OF ACTION

• Sulfonamides inhibit the enzymatic conversion of pteridineand p-aminobenzoic acid (PABA) to dihydropteroic acid by competing with PABA for binding to dihydrofolate synthetase, an intermediate of tetrahydrofolic acid (THF) synthesis. THF is required for the synthesis of purines and dTMP and inhibition of its synthesis inhibits bacterial growth. Pyrimethamine and trimethoprim inhibit dihydrofolate reductase, another step in THF synthesis, and therefore act synergistically with the sulfonamides.

COTRIMOXAZOLE SIDE EFFECTS

CLINICAL CONSIDERATIONS IN CHEMOTHERAPY

• 1.All cell wall inhibitors are Beta-lactams (penicllins, cephalosporins etc) except• vancomycin.

• 2. All penicllins are water soluble except nafcillin.

• 3. All protein synthesis inhibitors are bacteriostatic, except for the aminoglycosides

• 4. All cocci are gram positive, except Neisseria spp.

• 5. All bacilli are gram negative, except anthrax, tetanus, botulism and diphtheria bugs

• 6. All spirochaetes are gram negative

• 7.Tetracylcines and macrolides are used for intracellular bacteria

• 8.Beware pregnant women and tetracylcines, aminoglycosides, fluoroquinolones and • sulfonamides.

• 9.Antibitoics beginning with 'C' are particularly associated with pseudomembranous colitis i.e. Cephalosporins, Clindamycin and Ciprofloxacin.

• 10. While the penicillins are the most famous for causing allergies, a significant proportion of people with penicillin allergies may also react to cephalosporins. These should therefore also be

• avoided.

CLINICAL CONSIDERATIONS IN CHEMOTHERAPY

END THANKS

Created by Pharmacologist L. Mweetwa for:

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