Is there a negative interaction between bactrim (sulfamethoxazole and trimethoprim) ds and coumadin?

Yes: Bactrim (sulfamethoxazole and trimethoprim) ds increases effects of Coumadin by decreasing metabolism, by plasma protein binding competiton, and through hepatic enzyme cyp2c9/10 metabolism. Significant interaction possible.Monitor closely. Use alternatives if available.

Interaction checker: You can use a drug interaction checker whenever you have questions about drug-drug interactions or drug - food interactions. Here is one option (Drugs.Com): https://www.drugs.com/drug_interactions.php Your pharmacist is also an excellent source of information.