Which medication may interact with dabigatran?

• A. Ciprofloxacin
• B. Fluoxetine
• C. Simvastatin
• D. Carbamazepine

Answer: (D)

The interaction being tested involves how dabigatran exposure changes with drugs that affect the P-glycoprotein (P-gp) transporter. Dabigatran etexilate is a substrate of P-gp, and its absorption and elimination depend on P-gp activity. When a drug induces P-gp, more dabigatran is pumped back into the intestinal lumen and/or eliminated, lowering plasma concentrations and potentially reducing anticoagulant effect.

Carbamazepine is a potent inducer of P-gp (and other transporters), so it can markedly decrease dabigatran levels, compromising anticoagulation and increasing thromboembolic risk. This makes it the best answer.

Ciprofloxacin, fluoxetine, and simvastatin can interact with dabigatran through different mechanisms, but they do not produce the same induction of P-gp that lowers dabigatran exposure to a clinically meaningful degree; some can even increase dabigatran levels if they inhibit P-gp, which would raise bleeding risk rather than reduce efficacy.