SPEX SPEX Pharmacology 4

Question 1

A patient on warfarin begins taking trimethoprim-sulfamethoxazole for a UTI. What is the most likely effect on warfarin's anticoagulant activity?

Accepted Answer

Increased anticoagulation due to enzyme inhibition

Answer

TMP-SMX inhibits CYP2C9, the primary enzyme metabolizing warfarin's S-enantiomer, leading to elevated INR and increased bleeding risk.

Question 2

Which mechanism best explains tachyphylaxis to nitrate therapy used for angina?

Accepted Answer

Depletion of sulfhydryl groups needed for nitric oxide formation

Answer

Continuous nitrate exposure depletes sulfhydryl (–SH) groups required for conversion to nitric oxide, resulting in diminished vasodilatory response.

Question 3

A 68-year-old with stage 3 CKD is prescribed metformin. Which concern is most clinically relevant?

Accepted Answer

Lactic acidosis due to reduced renal clearance

Answer

Metformin is renally cleared, and accumulation in CKD raises plasma levels that promote anaerobic metabolism and life-threatening lactic acidosis.

Question 4

Which pharmacokinetic parameter best predicts the risk of drug accumulation in a patient receiving multiple doses?

Accepted Answer

Half-life

Answer

Half-life determines the time to reach steady state and the extent of accumulation; drugs with long half-lives accumulate more with repeated dosing.

Question 5

A physician prescribes fluconazole to a patient already taking cisapride. Why is this combination contraindicated?

Accepted Answer

Fluconazole inhibits CYP3A4, raising cisapride levels and risking torsades de pointes

Answer

Fluconazole is a potent CYP3A4 inhibitor; cisapride relies on CYP3A4 for clearance, so co-administration elevates cisapride concentrations and prolongs QT, potentially causing fatal arrhythmia.

SPEX Exam Practice Test

SPEX Exam Practice Test

SPEX SPEX Pharmacology 4