Which drug combination is described as causing a clinically significant interaction?

• A. Warfarin, Ramipril
• B. Digoxin, Amiodarone
• C. Amitriptyline, Loperamide
• D. Clarithromycin, Ramipril

Answer: (B)

The key idea is that some drug pairs markedly raise the level of one drug, increasing toxicity risk. Digoxin is cleared mainly by the kidneys and depends on P-glycoprotein for transport. Amiodarone strongly inhibits P-glycoprotein (and can affect other drug transport and metabolism). When given together, amiodarone can reduce digoxin clearance, causing higher digoxin blood levels and a greater risk of toxicity. Digoxin toxicity can present with nausea, confusion, visual disturbances, and potentially dangerous heart rhythm problems like bradycardia or arrhythmias. Because of this, the combination is a well-recognized clinically significant interaction and often requires close monitoring, dose adjustment, or avoidance.

Other pairs don’t have this same well-established, consistent interaction pattern. For example, warfarin with an ACE inhibitor can raise bleeding risk in some cases but isn’t a classic, predictable pharmacokinetic interaction; amitriptyline with loperamide may raise anticholinergic or constipating effects but isn’t a definitive, high-risk interaction; clarithromycin with an ACE inhibitor isn’t known for a strong, consistent interaction in the same way as digoxin with amiodarone.