Drug Interactions and Adverse Effects Flashcards

A patient taking a nonselective MAOI consumes aged cheese. What mechanism underlies the resulting hypertensive crisis?

Answer: Tyramine accumulation triggers massive norepinephrine release

MAOIs block intestinal and hepatic monoamine oxidase, preventing first-pass tyramine metabolism; absorbed tyramine displaces norepinephrine from sympathetic nerve terminals, causing massive catecholamine release and hypertensive crisis.

Which antituberculosis agent most commonly causes peripheral neuropathy that can be prevented with pyridoxine supplementation?

Answer: Isoniazid

Isoniazid competitively inhibits pyridoxine phosphorylation, creating a functional vitamin B6 deficiency that impairs myelin synthesis and causes peripheral neuropathy; coadministration of pyridoxine 25–50 mg/day prevents this adverse effect.

A woman taking combination oral contraceptives begins rifampin for tuberculosis treatment. What is the expected clinical outcome?

Answer: Reduced contraceptive efficacy with risk of unintended pregnancy

Rifampin induces CYP3A4 and P-glycoprotein, dramatically accelerating the metabolism of ethinyl estradiol and progestins, reducing hormone levels below the contraceptive threshold.

Which electrolyte abnormality is most commonly associated with thiazide diuretic therapy?

Answer: Hypokalemia

Thiazides increase sodium and water delivery to the distal collecting duct, stimulating aldosterone-mediated potassium secretion and resulting in clinically significant hypokalemia, particularly dangerous in patients also taking digoxin.

Coadministration of clopidogrel and omeprazole raises concern primarily because:

Answer: Omeprazole inhibits CYP2C19, reducing conversion of clopidogrel to its active metabolite

Clopidogrel is a prodrug requiring CYP2C19-mediated bioactivation to its active thiol metabolite; omeprazole's inhibition of CYP2C19 reduces active metabolite formation, potentially diminishing antiplatelet efficacy.

Beta-blockers mask most adrenergic symptoms of hypoglycemia. Which symptom is notably PRESERVED because it is mediated by the cholinergic nervous system?

Answer: Diaphoresis (sweating)

Beta-blockers block adrenergically mediated hypoglycemia symptoms (tachycardia, tremor, palpitations) but diaphoresis is mediated by cholinergic sympathetic fibers that are unaffected by beta-blockade, making sweating a useful remaining warning sign.

Co-administration of valproic acid with lamotrigine results in which clinically important pharmacokinetic interaction?

Answer: Valproic acid inhibits UGT-mediated lamotrigine glucuronidation, approximately doubling its half-life

Valproic acid inhibits UDP-glucuronosyltransferase (UGT1A4/2B7), the enzymes responsible for lamotrigine conjugation; this doubles lamotrigine's half-life and plasma levels, necessitating a 50% lamotrigine dose reduction to avoid toxicity.