Ch 1-General Tox Principles Flashcards
What are the general types of toxicology tests?
- Acute toxicity
- Subacute
- Chronic
What are the special types of toxicology tests?
- Reproduction and fertility
- Teratogenicity
- Mutagenicity
- Carcinogenicity
- Skin, eye, or muscle irritation
- Hemolysis
What are the most commonly used species in safety testing?
Rats and dogs
What is an important factor in safety testing? What are target species?
- Cost is an important factor
- Target species are species that will be exposed to the compound
3 properties of a testing compound?
- Should be pure or as it is commercially produced
- A vehicle should be inert and does not alter the properties of the compound
- A control vehicle should be used
Dosages
- For subchronic and chronic toxicity usually 3 dose levels are used:
- High dose that produces clinical signs
- Mid-dose that produces mild toxicosis
- Low dose which is the largest dose that does not produce toxicosis
Acute toxicity tests:
What type of experiment is it?
Exposure amount/time?
Observation period?
Species tested?
- Is an acute LD50 or LC50 experiment depending on the species
- Single or multiple exposures w/in 24 hour period (usually 4h)
- Observation period is usually 1 day, but sometimes up to 14 days
- Usually more than one species of rodent is used
what are some examples of routes of exposure for acute toxicity?
intraperitoneal, intravenous, and subcutaneous injection; oral intubation; and dermal application
Subacute toxicity
The effect produced by daily exposure from one day to 30 days
Subchronic toxicity testing:
Exposure period?
Dosages?
Group size/division?
Analyses?
Postmortem?
Other data?
- Period of exposure is 30-90 days (if there is delayed toxicity or cumulative toxicity from sub chronic studies - use addtional study for 6 months)
- Rats and dogs are usually used at 3 different dosages + a control group
- Rodents: size of the group is 30-40 animals equally divided by sex
- Dogs: size of the group is 6-10 equally divided by sex
- Hematologic and biochemical analyses are made at intervals
- Postmortem examination is performed at the end of the experiment
- Other data including weekly body weight, feed/water consumption, and clinical signs are also recorded
Single vs. repeat dose (graph)
Chronic toxicity testing
Similar to which test?
Exposure?
- Similar to the subchronic toxicity testing except the period of exposure is 90 days or more
- Usually up to 18 months in mice and 24 months in rats, dogs, or primates
- At least 1yr with repeat dosing
According to ICH S4 guidance what should be the duration of chronic tox test?
- 6 months rodents; 9 months non rodents
- for food additive with the potential for lifetime exposure in humans - 2 yrs
What is the conc. used in chronic testing and duration?
MTD (derived from sub-chronic testing for 90 days);
Chronic testing tyically >90 days
if there is delayed toxicity or cumulative toxicity from sub chrinic studies - use addtional study for 6 months
Reproduction and fertility tests
Effects of toxins at what stages?
How many generations of rats?
Testing process?
Parameters recorded?
- Tests the effects of toxicants on any stage of reproduction (ovulation, conception, implantation, gestation, embryo dev., fetal dev., parturition, lactation, and early embryonic growth)
- Usually 2-3 successive generations of rats are used
- Adult males are dosed for 60 days before mating, females 14 d before mating then females are also treated during gestation and lactation and the offspring are dosed from weaning until lactation
- The parameters recorded at each step include fertility index, length of gestation pd., live births, still births, survival at 5 days and at weaning, # of ea. sex, BW and gross abnormalities, microscopic examination of selected offspring
How is perinatal and post natal reproductive toxicity (Segment III) determined?
Administering the test chemical from 15d of gestation through delivery and lactation
(determine the effects effect on the
birth weight, survival, and growth of the offspring during the first 3 weeks)
Teratogenicity testing:
What is a teratogen?
Embryotoxic/fetotoxic substance?
Species?
Exposure specifics?
- Teratogen is any substance that produces non-lethal structural or functional abnormalities in the fetus
- Embryotoxic or fetotoxic is a substance that causes death of the embryo or fetus
- Testing is usually done in mice, rats, or rabbits
- The females are exposed to the tested compound during the period of organogenesis (organ dev.) (6-15 days of pregnancy in mice/rats and 6-18 days of pregnancy in rabbits)
What is the process of teratogenicity testing (4 steps)?
- The first day of gestation is determined in rats by sperm-positive vaginal smear and the presence of a vaginal plug in mice after mating with adult males overnight
- Fetuses are removed surgically one day before the expected day of parturition
- The fetuses are examined for gross changes, # of live and dead, # of resorptions, BW, sex, and any external malformations
- The fetuses are then examined for skeletal and visceral malformations
Mutagenicity–what is it? What are the 3 tests assoc. w/ it?
- Mutagenesis is the induction of chromosomal changes
- Dominant lethal test (in rodents)
- Cytologic tests
- Host-mediated microbial assay
Carcinogenicity testing:
Species?
Exposure?
Final stage?
- Tests are usually done in rats and mice
- Exposure to the tested compound is for the life of the animal and starts from weaning
- Animals are necropsied and the incidence of tumors is compared between the treated and control
Eye irritation testing
- Formulations used for the eye or if the eye will be exposed have to be tested for ocular irritation
- The drug is instilled in the conjunctival sac of one eye in an albino rabbit and the other eye serves as a control
- The tissue response is scored at periodic intervals of 72 hours
Skin irritation testing
- The test compound is applied on a shaved area of the skin of an albino rabbit
- The response is scored at periodic intervals
Injection irritation tests
For drugs used by IM, SC, or intramammary administration are tested for tissue irritation by evaluating inflammation or necrosis
Hemolysis testing
Required for what compounds?
Process?
- Required for compounds administered by the IV route
- The drug is administered intravenously and the hemoglobin content of a plasma sample one minute after injection is compared with that of a sample before injection
Chronicity factor (unitless expressed as mg/kg/day)
ratio between acute LD50 and chronic LD50
A chronicity factor greater than 2.0 (90) indicates a relatively cumulative toxicant
Chronicity factor 1.0 means no cumulative effect
Four types of toxic entities ( as per RM Yassine scale)
physical
biological (may be pathogens)
chemical
radiological
For hazadrous chemicals to be regulated
Consider:
1) NOAEL
2) TLVs -used by ACGIH (amts. to which a worker is exposed over lifetime without adverse effects)
3) BEIs (biological exposure indices)
4) RELs (recommended exposure limits)- by NIOSH
4) TDI/ ADI ( tolerable daily intake/ acceted daily intake)
Globally harmonized system for classification of toxicants (GHS)
Needed To avoid and minimize differences in
- types of tests
2 # of tests
- cuf-off thresholds etc.
across the world
Basis of GHS classification of toxicants
Based on
- Human health hazard
- Environmental health hazard
3) physical hazard (eg; from explosion etc.)
Classification of toxicants
Classified in terms of their
- physical state (gas, dust, liquid),
- chemical stability or reactivity (explosive, flammable, oxidizer),
- general chemical structure (aromatic amine, halogenated hydrocarbon, etc.),
- poisoning potential (extremely toxic, very toxic, slightly toxic, etc)
- biochemical mechanisms of action (e.g.,
alkylating agent, cholinesterase inhibitor, methemoglobin producer)
GHS classification- Human health hazard parameters
Acute toxicity [oral , dermal, inhalation (gas, vapor, mist)]
Skin corrosion
Eye irritation
Others ( respiratory sensitizers, allergens, carcinogens)
‘Toxicity class’ classificationT -for PESTICIDES ( by national or international government or sponsored organization)
WHO : Class I, II, III, 1V (aka extremely, highly moderately, slightly toxic)
EU: Class I-VIII (very toxic, toxic, harmful, corrosive, irritant, sensitizer, carcinogen,mutagen)
India: Toxicity labels
USA: Toxicity Class I, Toxicity Class II, Toxicity Class III, Toxicity Class IV, Toxicity Class V ( also General vs. Restricted use)
Points about ‘Toxicity class’ classification-for PESTICIDES in USA
put forth by USEPA (FIFRA)
Classes I to III are required to carry a signal word on the label
‘Toxicity labels’ classification- mainly for PESTICIDES in INDIA ( (based onInsecticides Act 1968 and Insecticides rule 1971)
Extremely toxic : 1 -50 mg/kg or less (RED label)
Highly toxic: 50-500 mg/kg (YELLOW label)
Moderately toxic: 501- 5000 mg/kg (BLUE label)
Slightly toxic: 5000 mg/kg (GREEN label)
Labels also have information:
A) brand name, B) name of manufacturer C) antidote
GHS classification- Environmental health hazard parameters
Soil
water
Air, .
Occupational hazard
highest non-toxic dose (HNTD)/ Maximum tolerated dose or minimal toxic dose (MDT)
The highest or largest dose which does NOT result in undesirable or toxic alterations (clinical, hematologic, biochemical, or pathologic alterations)
Toxic dose low (TDL)
The lowest dose which produces toxic alterations and administering twice this dose will NOT cause death
Toxic dose high (TDH)
The dose which produces toxic alterations and administering t_wice this dose will result in death_
No-effect level (maximum non toxic level)
The amount of a chemical that can be ingested without causing any deaths, illness or toxic alterations in any of the animals for the stated period (usually 90 days to 2 years or more depending on the species)
concerned directly with toxicity testing, which provides information for safety evaluation and regulatory requirements
descriptive toxicologist
ensures that materials shipped in interstate commerce are labeled and packaged in a manner consistent with the degree of hazard they present
DoT
immunologically mediated adverse reaction to a chemical resulting from previous sensitization to that chemical or to a structurally similar one
chemical allergy
allergic reaction= hypersensitivity
requires prior exposure
are allergic responses dose related?
YES
Amt of time tio syn Ab in case of allergic reactions
1-2 wks
Adverse effects/ deleterious effects/ toxic effects/ side effects
eg: drowsiness by “first-generation” antihistamine diphenhydramine (Benadryl)
most common allergic reaction in guinea pigs
bronchiolar constriction leading to asphyxia
refers to a genetically determined abnormal reactivity to a chemical
chemical idiosyncrasy
Toxic responses
immediate vs. delayed toxicity (most substances cause immediate toxicity)
local vs. systemic toxicity
reversible (if organ can regenerate) vs. irreversible (eg: CNS neurons, carcinogens)
Example of delayed toxicity
- Increased vaginal cancer risk in the daughters of women who were given diethylstilbestrol (DES) during pregnancy- risk after 20-30 yrs
- Delayed toxicity after exposure to OP pesticides
Cause of neurotoxicity from exposure to OP (eg: TOCP)
Due to modificaiton of the enzyme NTE (neuropathy target esterase) ——> this causes degeneration of long axons in the peripheral and CNS
Types of Antagonism ( Antagonists/Blockers)
Functional -two chemicals counterbalance each other by producing opposite effects on the same physiological function
Chemcial- a chemical reaction between two compounds that produces a less toxic product
Dispositional- Disposition of a chemical is altered so that the concentration and /or duration of the chemical at the target organ are diminished
Receptor- two ligands to the same receptor when given together antagonizes the effects of the second chemical
Tolerance
a state of decreased responsiveness to a toxic effect of a chemical resulting from prior exposure to that chemical or to a structurally related chemical
dispositional tolerance
Risk Assessment
Example of local toxoicity
At the site of action
eg:
- caustic substances
- irritant materials (eg Cl gas very little absorbed into blood)
Example of ststemic toxicity
- Most susbtances (except highly reactive substances) casue systemic tox
Substances causing local and systemic effects
eg:
- Tetra ethyl lead (skin burn and effects on CNS and other organs)
- Acid (skin burn and effects on kidneys)
Systemic toxicants
Most systemic toxicants affect
1-2 major target organs (sites if max toxicant conc).
eg:
lead on bone but effects are on CNS
DDT accumulates in adipose tissue
Most common target organs of systemic toxicants
CNS ( brain and spinal cord)
THEN
circulatory system (blood and hematopoietic system)
THEN
visceral organs (liver, kidney, and lung)
THEN
muscle , bone (last)
what is the one of the MOST IMPORTANT determinants of the extent of toxicity for local toxicants
- Route of administration (skin, gastrointestinal tract, or respiratory tract)
- Frequency of exposure
Descending order of effectiveness for the routes of administration
- intravenous,
- inhalation,
- intraperitoneal,
- subcutaneous,
- intramuscular,
- intradermal,
- oral,
- and dermal
How do most occupational exposures occur?
Inhalation
Skin
if toxic dose after oral or dermal administration is similar to the TD after intravenous administration what does it imply?
that the compound is readily absorbed
Antagonistic effects of chemicals are often very desirable in toxicology and are the basis of many antidotes
