Because Mr. Casagrand has a prosthetic heart valve, he must take warfarin sodium [Coumadin] 5 mg PO daily. Concomitant administration of trimethoprim-sulfamethoxazole [Bactrim] and warfarin can cause:

Enhanced Bactrim absorption, increasing the risk of toxicity

Decreased Bactrim effectiveness, requiring a dosage increase

Displaced Warfarin, increasing its effects

Increased Warfarin excretion, decreasing its effects