Pharm.D. Doctor of Pharmacy Drug Interactions and Adverse Effects 1 — Questions and Answers
Question 1: Which mechanism explains the interaction between rifampin and oral contraceptives?
- Rifampin inhibits CYP3A4, increasing contraceptive levels
- Rifampin induces CYP3A4, accelerating estrogen metabolism and reducing contraceptive efficacy (Correct answer)
- Rifampin competes for protein binding with estrogen
- Rifampin blocks gut absorption of hormonal contraceptives
Correct answer: Rifampin induces CYP3A4, accelerating estrogen metabolism and reducing contraceptive efficacy
Rifampin is a potent CYP3A4 inducer that accelerates the hepatic metabolism of estrogen and progestin in oral contraceptives, significantly reducing their plasma levels and contraceptive efficacy.
Question 2: Which adverse effect is specifically associated with aminoglycoside antibiotics and requires regular monitoring?
- Hepatotoxicity and elevated LFTs
- Nephrotoxicity and ototoxicity (Correct answer)
- Pulmonary fibrosis
- Stevens-Johnson syndrome
Correct answer: Nephrotoxicity and ototoxicity
Aminoglycosides (e.g., gentamicin, tobramycin) are associated with concentration-dependent nephrotoxicity and ototoxicity, requiring serum level monitoring and renal function assessment.
Question 3: A patient on sildenafil is prescribed a nitrate for angina. What is the primary concern?
- Reduced sildenafil efficacy
- Severe hypotension due to additive vasodilation (Correct answer)
- Increased risk of priapism
- Nitrate tolerance develops faster
Correct answer: Severe hypotension due to additive vasodilation
Both sildenafil (PDE5 inhibitor) and nitrates increase cGMP, causing profound additive vasodilation and potentially life-threatening hypotension — this combination is absolutely contraindicated.
Question 4: Which adverse effect is most concerning with long-term proton pump inhibitor (PPI) use?
- Hepatotoxicity
- Hypomagnesemia and increased risk of Clostridioides difficile infection (Correct answer)
- Renal tubular acidosis
- Peripheral neuropathy
Correct answer: Hypomagnesemia and increased risk of Clostridioides difficile infection
Long-term PPI use is associated with hypomagnesemia, hypokalemia, increased risk of C. difficile infection, and reduced absorption of calcium, vitamin B12, and iron.
Question 5: Which lab finding is characteristic of heparin-induced thrombocytopenia (HIT)?
- Elevated platelet count above 500,000/μL
- Platelet count drop of ≥50% from baseline, typically 5–14 days after heparin initiation (Correct answer)
- White blood cell count below 2,000/μL
- Elevated D-dimer with normal platelet count
Correct answer: Platelet count drop of ≥50% from baseline, typically 5–14 days after heparin initiation
HIT is characterized by a ≥50% platelet count drop from baseline occurring 5–14 days after heparin initiation due to antibodies against heparin-platelet factor 4 complexes.
Question 6: Which drug interaction mechanism is responsible for the increased bleeding risk when NSAIDs are combined with anticoagulants?
- NSAIDs induce CYP2C9, increasing anticoagulant metabolism
- NSAIDs inhibit platelet aggregation and may displace anticoagulants from protein binding sites (Correct answer)
- NSAIDs decrease vitamin K production
- NSAIDs increase anticoagulant renal clearance
Correct answer: NSAIDs inhibit platelet aggregation and may displace anticoagulants from protein binding sites
NSAIDs inhibit platelet aggregation by blocking thromboxane A2 synthesis and can displace highly protein-bound anticoagulants, increasing free drug levels and compounding bleeding risk.
