MAY PROLONG THE PROTHROMBIN TIME IN PATIENTS WHO ARE RECEIVING ANTICOAGULANTS, INCLUDING WARFARIN. SULFISOXAZOLE COMPETES WITH THIOPENTAL FOR PLASMA PROTEIN BINDING. PATIENTS RECEIVING SULFISOXAZOLE MIGHT REQUIRE LESS THIOPENTAL FOR ANESTHESIA. SULFONAMIDES CAN DISPLACE METHOTREXATE FROM PLASMA PROTEIN-BINDING SITES, THUS INCREASING FREE METHOTREXATE CONCENTRATIONS. STUDIES IN MAN HAVE SHOWN SULFISOXAZOLE INFUSIONS TO DECREASE PLASMA PROTEIN-BOUND METHOTREXATE BY ONE-FOURTH. SULFISOXAZOLE CAN ALSO POTENTIATE THE BLOOD SUGAR LOWERING ACTIVITY OF SULFONYLUREAS, AS WELL AS CAUSE HYPOGLYCEMIA BY ITSELF.