animal toxicity studies
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Transcript of animal toxicity studies
Why study toxicology???Benefit –risk ratio can be calculated
Prediction of therapeutic index
Therapeutic index= Maximum tolerated dose
Minimum curative dose
Smaller ratio, better safety of the drug
why do we require non clinical
studies IN ANIMALS before
ADMINISTERED to man??
Pharmacological effects are same in man as in animals
Toxic effect in species will predict adverse effects in man
Giving high doses in animals improves predictability to man
Risk assessment can be made by comparison of toxic doses
in test species with predicted therapeutic dose in man
Relevant Test Models
Pharmacodynamic responses
Pharmacokinetic profile
Species, sex, age of experimental animals
Susceptibility, sensitivity and reproducibility of test
system
In vitro: Isolated organs, tissues cell-cultures
Mechanism of effect in vivo
Types of toxicology studies
Systemic toxicology studies
Single dose studies Repeated dose studies
Reproductive toxicology studies
Male fertility Female reproduction & Developmental
studies
Local toxicity studies
Hypersensitivity studies
Genotoxicity studies
Carcinogenicity studies
A. Systemic toxicology studies
Preliminary Definitive
• Maximum Non
Lethal dose
(MNLD) determined
• MTD and MLD
determined
• Evaluate effects
• Target organ of toxicity
may be determined
a) SINGLE DOSE STUDIES/ ACUTE TOXICITY
Preliminary studies
METHOD
Single dose tested in 2 rodent species
2 routes of administration
Oral dosing of 2g/kg or 10 times of normal human dose
Observation for 14 days after dosing
MNLD established
Symptoms , signs reported
Microscopic and Macroscopic evaluation
Definitive studies
METHOD
Group of 20 animals of either sex dosed at MNLD
5 animals of each sex are observed for 48 hr and
conduct autopsy for early pathological changes
Remaining 5 of each sex are observed for 14 days
MTD and MLD established
Signs of intoxication or recovery, changes in body
weight, pathological changes
Complete macroscopic and microscopic examination
Target organs can be identified
Two mammalian species(one should be non-rodent)
Long duration studies (30-180 days)
Dose is dependent on dose-escalating studies
Drug administered by clinical route
Parameters monitored and recorded are:
Behavioral
Physiological
Biochemical
Microscopic observations
b) REPEATED DOSE STUDIES/SUB-ACUTE
OR CHRONIC TOXICITY
Chronic toxicity
Objectives To evaluate the cumulative toxicity of chemicals.
To assess carcinogenic potential.
DurationRodents - 6 to 24 months; non-rodents - 12 months or longer or up to 15 to 20% of species’ lifespan.
Test System/Animal System2 species required. Rodents, non rodents.
Parameters
Mortality
Pathology and histopathology
Weight change
Clinical pathology of all animals (mortalities and survivors)
B. Reproductive toxicology studies
a) MALE FERTILITY
METHOD
One rodent species(rat)
3 dose groups taken
(each with 6 adult males),
1 control
Drug treatment by clinical route for 28-72 days
Mated with females in 1:2 ratio
Females getting pregnant should be examined
After 13 days of gestation
All male animals sacrificed
•Weights of testis, epididymus recorded & examined for
their histology
•Sperms examined for motility & morphology
Segment I
13
Fertility and general reproductive performance study
Segment II Teratogenicity
Segment III Perinatal and post-natal study
Fertility and early embryonic development (rat) Embryo- foetal development (rat & rabbit)
Post natal development (rat) (post natal survival of offspring), growth parameters, vital senses, behavioral effects
b) FEMALE FETILITY
Drug administered to both males (28days) and females
(14 days) before mating
Implantation Embryogenesis
C. Local toxicity studies
Required when drug is administered by special
route (other than oral) in humans
Study design:
2 species along with control used
Dose dependent on dose escalating studies
3 dose levels
Types of local toxicity studies
Dermal toxicity studies
Dermal photo-toxicity
studies
Vaginal toxicity studies
Rectal tolerance studies
Rats & Rabbit
Local signs (erythema, oedema),
histological examination
Guinea pig
Used in treatment of leucoderma
Examination of erythema &
oedema formation
Rabbit or Dog
Observation of swelling,
histopathology of vaginal wall
Rabbit or Dog
Signs of pain, blood or mucous,
histology examination of rectal
mucosa
Ocular toxicity studies
Parenteral drugs
Inhalation toxicity studies
Albino Rabbit
Changes in cornea ,Iris &
aqueous humor, histological
examination of eye
For intravenous/
intramuscular/ subcutaneous/
intra-dermal injection
Sites of injection examined
grossly and microscopically
One rodent and non rodent
species
Acute , sub-acute and chronic
studies performed
Observation of respiratory rate
Histological examination of
respiratory passages, lung tissue
D. Allergenicity/hypersensitivity
toxicology studies
Guinea Pig
Maximization test
Local lymph node assay
Determination of Maximum non
irritant or minimum irritant dose
Evaluation of Erythema and
oedema
Mice of one sex(either male or
female)
Drug treatment given on ear skin
Auricular lymph node dissection
after 5 days
Increase in 3h-thymidine used for
evaluation
E. Genotoxicity studiesTo detect early tumorigenic effects in cases of chronic
illness
In vitro tests:
Test for gene mutation in Bacteria
Cytogenetic evaluation of chromosomal damage in
mammalian cells
E.g.; Ames’s Salmonella Assay detects increased
number of aberrations in metaphase chromosomes
DNA strand breaks, DNA repair or recombination,
Measurements of DNA adductsIn vivo tests:
Chromosome damage in rodent hematopoietic cells
E.g.; Micronucleus Assay
f. Carcinogenicity/ oncogenicity studies
Life-time Bioassays
Carcinogenicity studies are performed on:
Drug used for >6 months or frequent intermittent use for chronic diseases
Chemical structure of drug indicates carcinogenic potential
Therapeutic class of drugs which have produced positive carcinogenicity
Group sizes of 50 animals/sex at each of 3 dose levels
Control group is of double size
Record for onset of tumor development
Usually carried out for 24 months in rats and 18 months in mice (life span studies)
CONDUCT OF STUDY
EVALUATION OF RESULT
Incidence of cancers in control and test
Trend towards increasing incidence with increasing doses
Number of animals with single/multiple tumors
Macroscopic changes observed by autopsy
Histopathology of organs and tissues