Bactrim (sulfamethoxazole / trimethoprim) is a sulfa antibiotic that treats bacterial infections. The most common Bactrim side effects are nausea, diarrhea, and skin changes. Bactrim (sulfamethoxazole/trimethoprim) is a combination antibiotic that kills bacteria by blocking two steps in their production of essential nucleic acids. It treats urinary tract infections, ear infections, pneumonia, and intestinal infections. Learn about uses, side effects, dosage, and more for Bactrim. It's a prescription oral tablet used to treat certain types of infection in adults and some children. Bactrim (Trimethoprim and Sulfamethoxazole) may treat UTI, side effects, dosage, drug interactions, warnings, patient labeling, and more Find patient medical information for Sulfamethoxazole/Trimethoprim (Bactrim, Septra, and oothers) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user. Sulfamethoxazole/trimethoprim (TMP-SMX, Bactrim, Septra) treats a wide range of bacterial infections including urinary tract infections (UTIs), ear infections (pediatric), traveler's diarrhea, shigellosis, acute bronchitis exacerbations, and Pneumocystis jirovecii pneumonia (PCP). Bactrim is a combination of two antibiotics: sulfamethoxazole and trimethoprim. Bactrim is used to treat certain bacterial infections, such as pneumonia, bronchitis, traveler’s diarrhea, and infections of the ears, intestines, and urinary tract. Bactrim and Bactrim DS are antibiotics used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, shigellosis, and Pneumocystis jiroveci pneumonia. 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). BACTRIM is a combination of sulfamethoxazole, a sulfonamide antimicrobial, and trimethoprim, a dihydrofolate reductase inhibitor antibacterial, indicated in adults and pediatric patients two.