Toxicity Testing Flashcards
toxicity is an extension of a drug’s pharmacological action and therefore all toxic effects are predictable
true or false
true
Acute toxicity of a drug occurs after
a single dose
subacute or subchronic tox is after exposure to the drug for
days or weeks
chronic toxicity of drugs is observed after exposure for
months to years
what are the goals (5) of non-clinical safety evaluations?
- characterization of toxic effects with respect to target organs
- dose dependence of toxic effects, i.e. dose response relationship
- relationship to exposure
- reversal potential
- dose determination for human clinical trials
animal tox studies can be seen as risk reduction measures for clinical trials
True/false
True
How are tox studies performed, 6 key attributes of a well designed study.
- according to a protocol
- use toxic doses
- record functional, structural or biochemical abnormalities compared with a control group
- determine the No Adverse Effect Level
- determine Maximum Tolerated Dose
- Evaluate safety margin over the therapeutic dose range in man
what are the four types of tox studies often performed?
- Acute Tox - single dose
- Short term chronic - up to 3 months (Repeat Dose)
- Long term chronic - 1-2 years (Repeat Dose)
- Special: Mutagenicity, teratogenicity, carcinogenicity
what is a key pharmaceutical consideration for conducting tox studies?
you want your molecule or test article to be representative in terms of purity and formulation to that used in man or long term tox studies to ensure you get consistent and good results
what other factors about species choice and dosage schedule are important to understand when designing tox studies?
- species have different metabolic rates and toxic effects
- compare metabolic profile in chosen species with man
- justify choice
- understand the plasma concentration of drug in the animal model and compare with man
When conducting acute tox studies the following must be performed prior to starting the study?
dose ranging study to determine doses that will demonstrate toxic effects
acute tox studies (single dose studies) should include which routes of administration
parenteral, that planned to be used in man, and any other appropriate routes
acute tox studies must include: (4 things)
- 2 species
- have equal male to female ratio
- include observation of physical and behavioural changes
- performed for 7 days
Lethal dose studies determine
the LD50, or the dose at which 50% of the population dies
what are some criticisms of the LD50 Methodology (7 things)
- kill animals unnecessarily
- require a large number of animals to complete
- can achieve the same if not better results with less animals using geometric methods
- varies between species and within strains of the same species
- values can differ by 500x or more with age
- nutritional status influences results
- environmental factors such as acclimatization, light, humidity, temperature, noise, socialization can infuence results
Outline requirements for each of the following for Chronic toxicity studies (Repeat Dose):
- Duration
- route of admin
- Dose
- Species
- Observation
- QC
- Duration
- 3 months - 1 year
- ICHM3 6 months rodent, 9 months non-rodent for exposure > 6 months
- route of admin
- that used in man
- for inhalation or topical include parenteral
- Dose
- use dose that gives toxic effects but not lethal dose
- 5x the human dose
- a dose in between
- Species
- 2 species, equal male/female
- metabolism resembles man
- usually rats or dogs
- Observation
- body weight, food/water intake, behavioural
- biological such as urinalysis, CBC
- QC
- done under GLP
- test facility management
- procedures
- study director
- quality assurance and quality control
- raw data available, reviewed and retained
Teratogens are
compounds which impair fertility and pre or post natal development
teratogens have their highest effect during blastula stage or organogenesis stage
organogenesis
the impact of teratogens from conception to blastula stage is
is either lethal or not lethal
When are repro tox studies required
Reproduction development tox studies are required for any drug indicated for women of child bearing
this type of repro tox study involves the exposure of germ cells of males and females to mutagenic agents that may impair fertility
Fertility study
Fertility studies require
- pretreatment of animals prior to mating
- males 70 days
- females 14 days
the teratogenic effect of fertility studies is determined based upon
the number of non-viable implants and # surviving fetuses
describe elements of an effect on organogenesis repro tox study
- females exposed d6-16
- some sacrificed during exposure and observed for resorption and dead fetuses
- fetus are studied for abnormalities
- some litter
- litter observed for behavioral and developmental effect
repro tox studies for drugs for long term use must be studied over
2 generations
repro tox studies examing the effect on organogenesis must include this number and level of dose
- 3 dose levels
- maternal toxic dose
- pharmacological effect
- geometric mean in between
repro tox studies are commonly performed in these species
rat and rabbit
mutagenic studies are required to be performed under these circumstances
- if the drug reacts with nuclear DNA or if it can be transformed by metabolism to a reactive species
a mutagen is
capable of inducing stable heritable changes in DNA sequence of a cell or organism
Mutagenicity occurs in three ways
- point mutations - change of a base sequences
- structure breakage in chromosome - clastogenic activity
- chromosomal breakage - formation of additional nuclei
chemical mutations that occur in germ cells are____and in somatic cells are____
- teratogenic
- carcinogenic
what is the Ames test
- an in vitro assay used to determine if a compound is a potential carcinogen by assessing its mutagenic effect on bacteria
what is the basis of the the Ames test?
- uses a strain of bacteria which has a mutation that requires histadine to grow
- use media with minimal amount of histadine. When histadine is depleted, only those cells which are able to revert or mutate are able to grow
- if a mutagen is present the cells will grow
what are some criticisms of the ames test
- it is prokaryotic and doesn’t reflect the mammalian metabolic process
- does not work with compounds that are metabolicly processed into mutagens
what does the current ames test require?
- use of S9 rat mitochondria fraction and NADPH obtained from glc -6 phosphate and NADP
- multiple bacterial strains demonstrating different mutation types
- control with similar structure to the test article
- negative control to account for solvent effect
- 5 concentrations with 3 fold difference between, upper concentration limit 5 mg/plate
what are four other mutagenicity tests that can be conducted in vitro?
- metaphase chromosome abberation assay
- micronucleus test
- unschdeuled DNA synthesis
- sister chromatid exchange
when do carcinogenicity studies need to be conducted (5)
- for novel drugs
- long term use
- long half life
- persistent metabolites
- if any mutagenicity test is positive
long term invivo carcinogenicity tests usually include these species and are of this duration
- rats or mice
- 2 years of dosing and 130 weeks of observation
