Sulfamethoxazole and trimethoprim combination is used to treat infections including urinary tract infections, middle ear infections (otitis media), bronchitis, traveler’s diarrhea, and shigellosis (bacillary dysentery). This medicine is also used to prevent or treat Pneumocystis jiroveci pneumonia or Pneumocystis carinii pneumonia (PCP), a very serious kind of pneumonia. This type of pneumonia occurs more commonly in patients whose immune systems are not working normally, including cancer patients, transplant patients, and patients with acquired immune deficiency syndrome (AIDS).

Sulfamethoxazole and trimethoprim combination is an antibiotic. It works by eliminating the bacteria that cause many kinds of infections. This medicine will not work for colds, flu, or other virus infections.