A chronic toxicology study provides inferences about the long-term effect of a test substance in animals, and it may be extrapolated to the human safety of the test substance

1. Toxicity Studies
By
Sanman Samova
Samova.sanman@gmail.com

2. “All things are poison and nothing is without
poison, only the dose permits something not
to be poisonous.“
Paracelsus (1493-1541)
2
“The dose makes the poison”
therapeutic
effect
toxic
effectincreasing dose

3. Why DoToxicologyTesting
To check , weather Chemical which is exposed to human
are Safe or not.
To analze How much concentration isToxic.
Need to prove new drugs are safe:
■ Before first administration to humans
■ Before later clinical trials

4. ■ Toxicology tests are used to examine finished products such as
– pesticides,
– medications,
– food additives,
– packing materials
– their chemical
■ ingredients. Most tests involve testing ingredients rather than finished
products.

5. ■InVitroToxicology
Homogenate, Cell suspension
■InVivoToxicology
Animal models like Mice rat, rabbit etc

6. In vitro methods are widely used for:
■ Screening and ranking chemicals
■ Studying cell, tissue, or target specific effects
■ Improve subsequent study design

7. In vitro methods are usually
■ Less expensive to run than in vivo studies
■ Faster than in vivo studies
■ Somewhat less predictive of toxicity in intact
organisms

8. Cytotoxicity
Cytotoxicity = toxicity to cells
■ Many different types of cells can be used; cells from higher organisms
– (e.g., liver cells, blood cells); bacteria; fungi; yeast
■ Can be used to assess viability, structural effects, and/or function
– Structural – e.g., effects on membrane integrity
– Functional – e.g., effects on mitochondrial function
– Cell proliferation – decreases or increases

9. Other in vitro studies are used…
■ Dermal or OcularToxicity
■ Immunotoxicity
■ Metabolism and Kinetics

10. InVivoToxicology
PURPOSE
Establish a safe starting dose for clinical studies
Provide information on a drug-treatment regimen that
would produce the least toxicity
Assess target organ toxicity and its reversibility
Provide insight into biomarkers for clinical monitoring

11. DESCRIPTIONOFTHE METHOD
 Selection of animal species
 Housing and feeding conditions
 Preparation of animals
 Preparation of doses

12. Animal studies
Rat,
Mouse,
Dog,
Rabbits,
Hamsters,
Guinea-pigs
Etc etc…

13. ■ Animals should be of comparable age and within a
restricted weight range.
■ Randomly selected subgroups from the test batch of
animals should be checked for health status before the
start of the study, including
– Clinical veterinarian examination
– Blood chemistry
– Viral antibodies
– Necropsy for growth pathology and histology of selected tissues
and organs (lungs, GIT, liver and kidney)

14. Route of Exposure
■ Applied to the skin
■ Dripped into the eyes;
■ Injected intravenously,
■ Intramuscularly or
■ Subcutaneously,
■ Inhaled either
– by placing a mask over the animals and restraining them, or by placing them in an
inhalation chamber;
■ Administered orally,
– through a tube into the stomach, or simply in the animal's food. Doses may be given
once, repeated regularly for many months, or for the lifespan of the animal.
The substances to be tested toxicologically are

15. Monitoring for toxicity
 Clinical observation for signs of toxicity
 Periodic measurement of body weight
 Food and water consumption
 Peripheral blood haematology
 Blood chemistry
 Urine analysis
 Necropsy

16. – Acute,
■ Single Dose
– Sub-acute
■ Around 7 Days
– Sub chronic
■ 28-90 days
– Chronic
■ More than 90
Dosing Duration

17. Acute toxicity
"those adverse effects occurring following oral or
dermal administration of a single dose of a substance, or
multiple doses given within 24 hours, or an inhalation
exposure of 4 hours"

18. ■ Acute toxicity
– Acute toxicity refers to the effects on the whole body of a single
dose of a chemical (or several doses within a 24-hour period),
usually manifested over a period of 14 days.
– is studied by using a rising dose until signs of toxicity become
apparent.
– Acute toxicity tests must be carried out in two or more mammalian
species covering at least two different routes of administration.
– There are several different types of acute toxicity tests.
– The LD50 ("Lethal Dose 50 %") test is used to evaluate the toxicity
of a substance by determining the dose required to kill 50% of the
test animal population.

19. LD50 values for different toxins
Toxicity rating Example LD50 (mg/kg)
Slightly toxic
(5-15 g/kg)
Ethanol 8000
Moderately toxic
(0.5-5 g/kg)
Sodium chloride
Parathion
4000
1300
Very toxic
(50-500 mg/kg)
Aspirin
Paracetamol
300
300
Extremely toxic
(5-50 mg/kg)
Theophylline
Diphenhydramine
50
25
Super Toxic
(<5 mg/kg)
Potassium cynanide
Digoxin
Tetrodotoxin
Botulinum toxin
3
0.2
0.01
0.00001 (10 ng/kg !)

20. Acute toxicity data are used mainly to:
■ Identify lethal/toxic doses of chemicals for humans (primarily
for the regulatory purposes of classification and labelling)
■ ii) Indicate the mode of toxicity in humans, including the
susceptibility of key target organs
■ iii) Provide a rough guide for dose selection in repeat-dose
tests in animals.

21. ■ Repeated exposure studies vary in duration from a few
days to a lifetime of exposure.
■ It can be subdivided into
– Short term toxicity studies.
– Subchronic studies.
– Chronic studies.

22. ShortTerm Studies
■ Vary in length from a few days (7-9) up to 28 days.
■ Shorter studies (around 7 days), have sometimes referred to subacute
studies,
■ The daily dosages less than the acute doses and total duration is much
longer (and not below “sub”) than for the acute studies. So the term
subacute is not a preferred description.

23. Chronic toxicity testing
specific target organ/systemic toxicity arising from a
repeated exposure

24. ■ Repeated dose toxicity testing using oral administration of a test
substance in rodents for 28 and 90 days is used to evaluate
chronic toxic effects, primarily effects on various organ systems,
and to establish a no observed effect level
■ Chronic toxicity testing consists of oral, dermal, and inhalation
sub acute repeated dose studies (28‐day) and
subchronicrepeated dose studies (90‐day) in rodents

25. Chronic studies
■ Exposure of the test species to the test substance for their life
span, or greater part there of.The duration in rats is 24 months
and 7 years or more in dogs.
■ Because of high cost of such studies, the majorities are usually
conducted as a combined chronic and carcinogenicity studies.

26. ChronicToxicity
■ Used to determine the effects of the drug on specialized organ
systems (e.g., cardiovascular, respiratory, neurologic)
■ Used to determine the effects of long-term exposure to the
drug, including the ability to produce cancer.
■ May not be required for drugs that are intended for only short-
term use (e.g., antibiotics) and that are expected to have no
permanent effects on DNA.
■ ReproductiveToxicity/Teratogenicity
■ Evaluates effects on reproductive function and ability to
produce birth defects

27.  The identification of the hazardous properties of a chemical,
 The identification of target organs,
 Characterisation of the dose: response relationship,
 Identification of a no‐observed‐adverse‐effect level (NOAEL)
 The prediction of chronic toxicity effects at human exposure
levels,

28. Overview…
■ Initial considerations
■ Description of the method,
■ selection of animal species
■ Housing and feeding conditions
■ Preparation of animals
■ Preparation of doses
■ Observations
■ Ophthalmological examination
■ Body weight, food/water consumption and food
efficiency
■ Haematology and clinical biochemistry
■ Pathology gross necropsy
■ Histopathology

29. The endpoints
The endpoints for repeat dose testing consist of …
 an evaluation of clinical observations,
 blood analysis,
 whole body gross necropsy, and
 microscopic examination of all organs and
tissues (histopathology)

30. Thank You