Detailed drug Information for Septra DS. Includes common brand names, drug descriptions, warnings, side effects and dosing information. Bactrim may produce incorrect test results if you are monitoring the health of your kidneys with certain tests (such as creatinine). It may also interfere with blood tests to measure methotrexate (Trexall), a drug used to treat certain types of cancer, autoimmune diseases (such as rheumatoid arthritis), and psoriasis. Drug information on Bactrim, Bactrim DS, you are taking trimethoprim and sulfamethoxazole. This medication can cause unusual results Breast Cancer .