ABT Toxicokinetics and Metabolism 1

Question 1

Which pharmacokinetic parameter describes the fraction of an administered dose that reaches systemic circulation unchanged?

Accepted Answer

Bioavailability (F)

Answer

Bioavailability (F) is the fraction of an administered dose that reaches the systemic circulation unchanged, accounting for absorption and first-pass metabolism.

Question 2

Which cytochrome P450 enzyme is responsible for metabolizing the largest number of pharmaceutical drugs (approximately 30–40%)?

Accepted Answer

CYP3A4

Answer

CYP3A4 is the most abundant hepatic and intestinal CYP enzyme and metabolizes approximately 30–40% of clinically used drugs, making it a key site of drug-drug interactions.

Question 3

A chemical with a high volume of distribution (Vd > 10 L/kg) is most likely to be:

Accepted Answer

Highly lipophilic and distributed into peripheral tissues

Answer

A high volume of distribution indicates the drug is extensively distributed into peripheral tissues (fat, muscle), suggesting high lipophilicity or strong tissue protein binding.

Question 4

First-order elimination kinetics means that:

Accepted Answer

The rate of elimination is directly proportional to the drug concentration

Answer

In first-order kinetics, a constant fraction (not amount) of drug is eliminated per unit time; the rate of elimination is proportional to drug concentration, resulting in a constant half-life.

Question 5

The hepatic extraction ratio (ER) of a drug determines whether its clearance is sensitive to changes in:

Accepted Answer

Hepatic blood flow for high-ER drugs and protein binding for low-ER drugs

Answer

High extraction ratio (ER > 0.7) drugs have flow-limited clearance sensitive to hepatic blood flow, while low ER drugs (< 0.3) have capacity-limited clearance sensitive to enzyme activity and protein binding.

ABT - American Board of Toxicology Practice Test

ABT - American Board of Toxicology Practice Test

ABT Toxicokinetics and Metabolism 1