Drug Interactions and Adverse Effects Flashcards

A patient on metformin is scheduled for a CT scan requiring iodinated contrast. What is the primary pharmacokinetic concern?

Answer: Contrast-induced nephropathy impairs metformin excretion, raising lactic acidosis risk

Iodinated contrast can precipitate acute kidney injury, which impairs metformin's renal elimination; the resulting metformin accumulation shifts glucose metabolism toward anaerobic pathways and risks potentially fatal lactic acidosis.

Which serious musculoskeletal adverse effect is most strongly associated with fluoroquinolone antibiotics, particularly in elderly patients?

Answer: Tendinopathy and tendon rupture

Fluoroquinolones disrupt tenocyte metabolism and matrix metalloproteinase activity, predisposing tendons — most commonly the Achilles tendon — to degeneration and rupture, especially in older patients and those on corticosteroids.

Rifampin is a potent inducer of which CYP450 isoenzyme, accounting for the majority of its clinically significant drug interactions?

Answer: CYP3A4

Rifampin is among the most potent inducers of CYP3A4, the most abundant hepatic CYP enzyme, dramatically increasing the metabolism of drugs such as oral contraceptives, warfarin, antiretrovirals, and cyclosporine.

A post-MI patient is taking both warfarin and clopidogrel. What is the primary clinical concern of this combination?

Answer: Substantially increased risk of major bleeding

Warfarin reduces clotting factor synthesis while clopidogrel inhibits platelet aggregation; their combination produces additive antithrombotic effects and significantly elevates the risk of major hemorrhagic events.

Why does hypokalemia potentiate digoxin toxicity?

Answer: Potassium and digoxin compete for the same binding site on Na+/K+-ATPase

Potassium competes with digoxin for binding to the cardiac Na+/K+-ATPase; when serum potassium is low, digoxin binds more avidly to the pump, amplifying both therapeutic and toxic effects at normal drug concentrations.

Which antibiotic is contraindicated with tizanidine due to inhibition of CYP1A2, causing potentially dangerous elevations in tizanidine levels?

Answer: Ciprofloxacin

Ciprofloxacin is a potent CYP1A2 inhibitor; since tizanidine is primarily metabolized by CYP1A2, this combination can cause a 10-fold increase in tizanidine exposure, leading to profound hypotension and sedation.

Which metabolic adverse effect most commonly results from long-term systemic corticosteroid therapy?

Answer: Hyperglycemia and steroid-induced diabetes

Corticosteroids stimulate hepatic gluconeogenesis, impair insulin signaling at peripheral tissues, and promote glycogenolysis, collectively causing hyperglycemia that can progress to steroid-induced diabetes mellitus.