Bactrim (sulfamethoxazole / trimethoprim) is a sulfa antibiotic that treats bacterial infections. The most common Bactrim side effects are nausea, diarrhea, and skin changes. Find patient medical information for Sulfamethoxazole/Trimethoprim (Bactrim, Septra, others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user. 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. Bactrim (Trimethoprim and Sulfamethoxazole) may treat UTI, side effects, dosage, drug interactions, warnings, patient labeling, and more Trimethoprim/sulfamethoxazole, sold under the trade names Bactrim, Cotrim (a short form of the British Approved Name, Co-trimoxazole) and Septra, among others, is a fixed-dose combination antibiotic medication used to treat a variety of bacterial infections. [2] 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). Trimethoprim-sulfamethoxazole (TMP-SMX), also known as co-trimoxazole, is a combination of two antimicrobial agents that act synergistically against a wide variety of bacteria. Although other combinations of sulfonamides are available with trimethoprim, TMP-SMX is by far the most widely used. Sulfamethoxazole/trimethoprim (sometimes known as SMZ/TMP) is a combination medication containing an antifolate and sulfa antibiotic. It's used to treat different types of infections, such as urinary tract infections (UTIs), ear infections, and lung infections. Bactrim and Bactrim DS are antibiotics used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, shigellosis, and Pneumocystis jiroveci pneumonia. 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.