SUSPECTED TRIMETHOPRIM-SULFAMETHOXAZOLE INDUCED HYPOPROTHROMBINEMIA

The following report illustrates a case of trimethoprim/sulfamethoxazo le-induced hypoprothrombinemia in a patient receiving ongoing warfarin therapy for atrial fibrillation and aortic valve replacement. He was treated with trimethoprim/sulfamethoxazole (TMP/SMX) for sinusitis. Du ring this time, the patient's prothrombin time international normalize d ratio (INR) increased 3.5 times higher than the baseline value. The INR values decreased when the antibiotic was discontinued. If a patien t is on warfarin and TMP/SMX is added, INR values should be monitored closely.