Drug Interactions Newsletter

Volume 1, Issue 5, 02/17/2009

Question

How does trimethoprim/sulfamethoxazole (Bactrim™;Bactrim™DS; Septra® DS) result in clinically significant increases in the INR in patients on stable doses of warfarin (Coumadin®; Jantoven®) and thereby put them at significant risk for bleeding?

Answer

Warfarin (Coumadin®; Jantoven®) is an oral anticoagulant most commonly used for the prevention and treatment of thromboembolic events (blood clots) in patients with atrial fibrillation, prosthetic heart valves, venous thrombosis and/or pulmonary embolism.(1) Trimethoprim/Sulfamethoxazole (TMP/SMX) is an oral antibiotic most commonly used to treat respiratory, urinary tract and skin infections.(2-5)  Because TMP/SMX is one of the most frequently prescribed antibiotics, the opportunities for coadministration with warfarin are quite prevalent.(6)......To read the full answer please LOGIN or SUBSCRIBE NOW.