AU )  C ( US ) Legal status ℞ -only   ( US ) Routes Oral Co-trimoxazole  (abbreviated SXT, TMP-SMX, TMP-SMZ or TMP-sulfa) is a  sulfonamide antibiotic  combination of  trimethoprim  and  sulfamethoxazole , in the ratio of 1 to 5, used in the treatment of a variety of bacterial infections. The