The effect of furosemide and bumetanide on warfarin metabolism and anticoagulant response.

In a study of 11 normal subjects who received either furosemide or bumetanide, response to warfarin was unaffected by either diuretic. The mean prothrombin times after a single oral dose of 50 mg warfarin were 18.8 +/- 0.7 sec before and 19.6 +/- 1.7 sec during furosemide administration, and 18.3 +/- 1.4 sec before and 19.7 +/- 1.3 sec during bumetanide administration. Mean plasma warfarin half-lives were 43.2 +/- 2.8 hr before and 37.8 +/- 1.7 hr during furosemide treatment and 39.9 +/- 9.5 hr before and 37.4 +/- 2.4 hr during bumetanide treatment. Hypoprothrombinemic responses, plasma warfarin concentrations, and warfarin half-lives were not significantly influenced by treatment with either diuretic. Both loop diuretics furosemide and bumetanide can be safely administered during warfarin anticoagulant therapy without risk of clinically significant interaction.