Principles of Toxicology Flashcards
Five identical experimental animals are treated with 1 mg of one of the following toxins.
The animal treated with which toxin is most likely to die?
a. ethyl alcohol (LD50 = 10,000 mg/kg).
b. botulinum toxin (LD50 = 0.00001 mg/kg).
c. nicotine (LD50 = 1 mg/kg).
d. ferrous sulfate (LD50 = 1500 mg/kg).
e. picrotoxin (LD50 = 5 mg/kg).
B. The lower the LD₅₀, the more toxic the substance. Botulinum toxin has an extremely low LD₅₀, meaning it’s highly lethal even in microgram quantities.
Place the following mechanisms of toxin delivery in order from most effective to least
effective—1: intravenous; 2: subcutaneous; 3: oral; 4: inhalation; 5: dermal.
a. 1, 5, 2, 4, 3.
b. 4, 1, 2, 3, 5.
c. 1, 4, 2, 3, 5.
d. 4, 2, 1, 5, 3.
e. 1, 4, 3, 2, 5.
Correct Answer: C. 1 (IV), 4 (inhalation), 2 (subcutaneous), 3 (oral), 5 (dermal)
Explanation:
IV = 100% bioavailability
Inhalation = rapid absorption
SubQ = moderate
Oral = reduced by first-pass metabolism
Dermal = least efficient (skin is a strong barrier)
A toxin with a half-life of 12 h is administered every 12 h. Which of the following is true?
a. The chemical is eliminated from the body before the next dose is administered.
b. The concentration of the chemical in the body will slowly increase until the toxic
concentration is attained.
c. A toxic level will not be reached, regardless of how many doses are administered.
d. Acute exposure to the chemical will produce immediate toxic effects.
e. The elimination rate of the toxin is much shorter than the dosing interval.
Correct Answer: b. The concentration of the chemical in the body will slowly increase until the toxic concentration is attained.
Explanation:
When the dosing interval equals the half-life, the substance accumulates over time until steady-state is reached.
Urushiol is the toxin found in poison ivy. It must first react and combine with proteins in the
skin in order for the immune system to recognize and mount a response against it. Urushiol
is an example of which of the following?
a. antigen.
b. auto-antibody.
c. superantigen.
d. hapten.
e. cytokine.
D. Urushiol is a small molecule that must bind to skin proteins to elicit an immune response. Haptens are not immunogenic alone, but become immunogenic when attached to proteins.
Toxic chemicals are most likely to be biotransformed in which of the following organs?
a. central nervous system.
b. heart.
c. lung.
d. pancreas.
e. liver.
Correct Answer: e. liver
Explanation:
The liver is the primary site for metabolism via Phase I (e.g., CYP450s) and Phase II reactions.
When chemicals A and B are administered simultaneously, their combined effects are far
greater than the sum of their effects when given alone. The chemical interaction between
chemicals A and B can be described as which of the following?
a. potentiative.
b. additive.
c. antagonistic.
d. functionally antagonistic.
e. synergistic
Correct Answer: e. synergistic
Explanation:
Synergistic = combined effect greater than additive.
Additive = A + B = expected sum.
Potentiation = one agent with no effect increases the effect of another.
With respect to dose–response relationships, which of the following is true?
a. Graded dose–response relationships are often referred to as “all or nothing” responses.
b. Quantal dose–response relationships allow for the analysis of a population’s response to
varying dosage.
c. Quantal relationships characterize the response of an individual to varying dosages.
d. A quantal dose–response describes the response of an individual organism to varying
doses of a chemical.
e. The dose–response always increases as the dosage is increased.
Correct Answer: b. Quantal dose-response relationships allow for the analysis of a population’s response to varying dosage.
Explanation:
Quantal = “all or none” outcomes (e.g., % of a population showing response at each dose).
Graded = continuous response in one organism.
When considering the dose–response relationship for an essential substance:
a. there are rarely negative effects of ingesting too much.
b. the curve is the same for all people.
c. adverse responses increase in severity with increasing or decreasing dosages outside of
the homeostatic range.
d. the relationship is linear.
e. deficiency will never cause more harm than over-ingestion.
Correct Answer: c. adverse responses increase in severity with increasing or decreasing dosages outside of the homeostatic range.
Explanation:
Essential nutrients follow a U-shaped curve — both deficiency and excess can be harmful.
The therapeutic index of a drug:
a. is the amount of a drug needed to cure an illness.
b. is lower in drugs that are relatively safer.
c. describes the potency of a chemical in eliciting a desired response.
d. describes the ratio of the toxic dose to the therapeutic dose of a drug.
e. explains the change in response to a drug as the dose is increased.
Correct Answer: d. describes the ratio of the toxic dose to the therapeutic dose of a drug.
Explanation:
TI = TD₅₀ / ED₅₀. A higher TI means greater safety.D.
Explanation:
TI = TD₅₀ / ED₅₀. A higher TI means greater safety.
Penicillin interferes with the formation of peptidoglycan cross-links in bacterial cell walls, thus weakening the cell wall and eventually causing osmotic death of the bacterium. Which
of the following is true?
a. Treatment with penicillin is a good example of selective toxicity.
b. Penicillin interferes with human plasma membrane structure.
c. Penicillin is a good example of a drug with a low therapeutic index.
d. Penicillin is also effective in treating viral infections.
e. Penicillin is completely harmless to humans.
Correct Answer: a. Treatment with penicillin is a good example of selective toxicity.
Explanation:
Penicillin targets bacterial cell walls (peptidoglycan), which humans lack, making it selectively toxic
