Pharmacy Pharmacokinetics 3

Question 1

Which CYP450 enzyme is responsible for metabolizing the largest proportion of clinically used drugs?

Accepted Answer

CYP3A4

Answer

CYP3A4 is the most abundant hepatic CYP enzyme and is responsible for the metabolism of approximately 50% of all clinically used drugs.

Question 2

Co-administration of a potent CYP3A4 inhibitor with a CYP3A4 substrate drug would be expected to:

Accepted Answer

Increase plasma concentrations of the substrate, raising toxicity risk

Answer

A CYP3A4 inhibitor blocks the enzyme responsible for substrate metabolism, causing decreased clearance and elevated plasma concentrations, which can lead to toxicity.

Question 3

Which of the following is a classic example of a prodrug that requires CYP2C19-mediated hepatic activation for antiplatelet effect?

Accepted Answer

Clopidogrel

Answer

Clopidogrel is an inactive prodrug converted by CYP2C19 to its active thiol metabolite; poor metabolizers of CYP2C19 have reduced antiplatelet response and increased cardiovascular risk.

Question 4

In elderly patients, which pharmacokinetic change most commonly leads to drug accumulation and toxicity with renally eliminated drugs?

Accepted Answer

Decreased renal clearance (reduced GFR)

Answer

GFR declines progressively with age (approximately 1 mL/min/year after age 40), making renally cleared drugs accumulate to higher levels in elderly patients without dose adjustment.

Question 5

Therapeutic drug monitoring (TDM) of aminoglycosides typically involves measuring which levels?

Accepted Answer

Peak and trough serum concentrations

Answer

Traditional aminoglycoside TDM measures both peak (for efficacy — concentration-dependent killing) and trough levels (to minimize nephrotoxicity and ototoxicity).

Pharmacy Practice Test

Pharmacy Practice Test

Pharmacy Pharmacokinetics 3