Bactrim, an antibacterial combination drug, is prescribed for the treatment of certain urinary tract infections, severe middle ear infections in children, long-lasting or frequently recurring bronchitis in adults that has increased in seriousness, inflammation of the intestine due to a severe bacterial infection, and traveler's diarrhea in adults. Bactrim is also prescribed for the treatment of Pneumocystis carinii pneumonia, and for prevention of this type of pneumonia in people with weakened immune systems.