To accomplish a desired systemic effect, drug molecules must reach the systemic circulation after extravascular administration. The percent of the taken dose that reaches intact to the systemic circulation is called “bioavailability, BA”. Absolute Bioavailability compares the BA of the active drug in systemic circulation following non-intravenous administration
2. Toxicology
Discipline overlapping with biology, chemistry,
pharmacology and medicine
Study of the adverse effects of chemical
substances on living organisms
Practice of diagnosing and treating exposures to
toxins and toxicants
2
3. Why? For drug development
Pharmaceutical drugs- Must undergo preclinical
general toxicology studies
For providing information regarding the safety of
a potential new drug
Carried out before various clinical trials in
humans
Necessary for the approval of a new drug
3
4. Preclinical toxicology testing on various biological
systems reveals the species, organ and dose
specific toxic effects of an investigational product
The toxicity of a substance is observed by
A)Studying the accidental exposures to a
substance
B)in vitro studies using cells/ cell lines
C)in vivo exposure on experimental animals
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5. Steps
Acute toxicity
Chronic toxicity
Reproductive toxicity and teratogenecity
Mutagenecity and carcinogenicity
Immunotoxicity
Local tolerance
Duration- 1 year
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6. 1. Acute toxicity
To determine the effect of a single dose on a
particular animal species
Carried out in two different animal species
1 rodent and 1 non- rodent
Investigational product is administered at different
dose levels
All mortalities caused are recorded
Topical preparations, inhalation, skin 6
7. 2. Chronic toxicity
Require large number of animals
Can last up to two years
Demand only administration of drug paranterally
Studies lasts for 1-4 weeks to assess drug level
required to induce an observable toxic effect
Three different dosage level are used
Highest level should show an observable toxic effect
but lowest level should not induce any ill effect 7
8. Blood and urine analysis undertaken periodically
Complicated by the immune response in the
recipient animals
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9. Sub-chronic toxicity
Repeated dose 90 day oral toxicity testing
Rodents and non- rodents are used
Test substance is administered orally for 90 days
Weight variation- weekly
Biochemical characters, cardio vascular
parameter changes, behavioral changes- monthly
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10. Animals are sacrificed at end of the study
Gross pathological changes are observed
Tissues- Histopathological studies
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11. 3. Reproductive toxicity and teratogenecity
Entails ongoing administration of the proposed
drug at 3 different dosage level(Non toxic to
slightly toxic)
Nature of any effect of the substances on the
male and female reproductive system
Drug is administered one full spermatogenesis
cycle in male
Females are dosed for at least 14 days before
they mate 11
12. Assess male spermatogenesis
Female follicular development as well as
fertilization
Implantation and early fetal development
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13. 4. Mutagenecity and carcinogenecity
DNA damage -either by inducing alteration in
chromosomal structure or by promoting changes
in the nucleotide base sequence
Mutagenecity are necessary in the case of
chemical based drugs but in the case of
biopharmaceutical, mutagenecity test are being
done if any excipient (Substances other than
active ingredient) added to the final product.
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15. 6. Local tolerance
Test should be conducted if the route of
administration is SC or IM injection
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16. Animal models used for study
1. Nonhuman primates- Relevant
Used to assess the safety of a
biopharmaceutical
2. Rodent species- based on a reasonable target
homology
A biological drug should undergo toxicity testing to
support entry into the clinic and further clinical
development, and marketing approval.
Such testing is in agreement with international
regulatory guidance given by the International
Conference on Harmonization
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17. Repeated-dose general toxicology
studies in rodents and nonrodents
A standard design, with assessment of clinical signs, body
weight, food consumption, toxicokinetics,
ophthalmology, clinical pathology (hematology, clinical
chemistry, and urinalysis), organ weights, macroscopic
examination, and histopathology, along with
electrocardiogram (ECG) when the nonrodent is used.
Assessment in studies to support early clinical trials
generally involves
1.One vehicle-treated control group
2.Three drug-treated (low, mid, and high) groups 17
18. Assessment of the presence of antidrug antibodies
Necessary for determining whether systemic
exposure to the biopharmaceutical is maintained
at clinically relevant levels throughout the
duration of the dosing periods
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19. In vitro v/s in vivo studies
A similar response in human and animal cells in vitro is not
necessarily a guarantee that the in vivo response will be
similar.
In practice, this means that animal studies with highly
species-specific pharmaceutical products may:
•not reproduce the intended pharmacological effect in
humans;
•give rise to misinterpretation of pharmacokinetic and
pharmacodynamic results;
•not identify relevant toxic effects 19
20. Bioequivalence
It refers to the formulations of a drug with rates
and extents of absorption that are sufficiently
similar that there are not likely to be any
clinically important differences with respect to
either efficacy or safety
It is the property of two dosage forms or active
ingredients with similar blood concentration
levels that produce the same effect at the site of
physiologic activity 20
21. Bioequivalence studies are special type of studies
where two drugs or two sets of formulation of the
same drug are compared to show that they have
nearly equal bioavailability and PK/PD
parameters.
These studies are often done for generic drugs or
when a formulation of a drug is changed during
development.
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22. Example of non-bioequivalence
Digoxin, administered orally at the same dose of 1 mg
but as a tablet made by two different pharmaceutical
companies using different components, induced
quantitatively different pharmacological effects.
The two tablets were considered as nonbioequivalent
It was a consequence of the difference in formulation
between the two tablets, which released digoxin at
different rates and in different amounts. Thus, one
tablet could not replace the other.
22
23. Many pharmaceutical forms of the same drug are
now available, either during its development or as
generics
It need to be checked to see whether they will
produce the same quantitative effects
That is, one may be substituted for another
without any change in therapeutic effects.
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24. Checking bioequivalence
Assessed by the equivalence of the relative
bioavailabilities of the two pharmaceutical forms
of a drug
It is checked by comparing AUC, Cmax, and tmax,
assuming that pharmacokinetic parameters
remain constant during the comparison
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