SULFONAMIDES AND WARFARIN AND OTHER ORAL ANTICOAGULANTS
The anticoagulant effects of warfarin, acenocoumarol, and phenprocoumon are increased by co-trimoxazole (sulfamethoxazole with trimethoprim). Bleeding may occur if the anticoagulant dosage is not reduced appropriately. There is also evidence that sulfaphenazole, sulfafurazole (sulfisoxazole) and sulfamethizole may interact like co-trimoxazole.
The incidence of the interaction with co-trimoxazole appears to be high. If bleeding is to be avoided the INR should be well monitored and the warfarin, acenocoumarol, or phenprocoumon dosage should be reduced. Phenindione is said not to interact. The other interactions are poorly documented. However, it would seem prudent to follow the precautions suggested for co-trimoxazole if any sulfonamide is given with an oral anticoagulant.
The incidence of the interaction with co-trimoxazole appears to be high. If bleeding is to be avoided the INR should be well monitored and the warfarin, acenocoumarol, or phenprocoumon dosage should be reduced. Phenindione is said not to interact. The other interactions are poorly documented. However, it would seem prudent to follow the precautions suggested for co-trimoxazole if any sulfonamide is given with an oral anticoagulant.