SPEX Pharmacology Flashcards
7 cards from real SPEX practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 SPEX Pharmacology flashcards as text
A patient on warfarin begins taking trimethoprim-sulfamethoxazole for a UTI. What is the most likely effect on warfarin's anticoagulant activity?
Answer: Increased anticoagulation due to enzyme inhibition
TMP-SMX inhibits CYP2C9, the primary enzyme metabolizing warfarin's S-enantiomer, leading to elevated INR and increased bleeding risk.
Which mechanism best explains tachyphylaxis to nitrate therapy used for angina?
Answer: Depletion of sulfhydryl groups needed for nitric oxide formation
Continuous nitrate exposure depletes sulfhydryl (–SH) groups required for conversion to nitric oxide, resulting in diminished vasodilatory response.
A 68-year-old with stage 3 CKD is prescribed metformin. Which concern is most clinically relevant?
Answer: Lactic acidosis due to reduced renal clearance
Metformin is renally cleared, and accumulation in CKD raises plasma levels that promote anaerobic metabolism and life-threatening lactic acidosis.
Which pharmacokinetic parameter best predicts the risk of drug accumulation in a patient receiving multiple doses?
Answer: Half-life
Half-life determines the time to reach steady state and the extent of accumulation; drugs with long half-lives accumulate more with repeated dosing.
A physician prescribes fluconazole to a patient already taking cisapride. Why is this combination contraindicated?
Answer: Fluconazole inhibits CYP3A4, raising cisapride levels and risking torsades de pointes
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.
The concept of 'therapeutic index' is best described as:
Answer: The ratio of the toxic dose to the effective dose (TD50/ED50)
Therapeutic index = TD50/ED50; a higher value indicates a safer drug with a wider margin between therapeutic and toxic doses.
Which drug class directly inhibits the Na+/K+-ATPase pump to exert its pharmacological effect?
Answer: Cardiac glycosides
Cardiac glycosides (e.g., digoxin) inhibit Na+/K+-ATPase, increasing intracellular sodium, which indirectly raises intracellular calcium and enhances myocardial contractility.