Bactrim patient guide: sulfa allergy before first dose, MRSA skin infection use, and drug interactions. Bactrim, the fixed-dose combination of sulfamethoxazole (SMX) and trimethoprim (TMP) in a 5:1 weight ratio (typically 400 mg SMX / 80 mg TMP per standard tablet), represents a landmark example of rational combinatorial antibiotic design based on mechanistic pharmacology. Find patient medical information for Sulfamethoxazole/Trimethoprim (Bactrim, Septra, others) on WebMD including its uses, side effects and safety, interactions. Bactrim is a combination antibiotic medication. Bactrim can cause digestive issues and other side effects, including skin problems. Description 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. Bactrim (sulfamethoxazole and trimethoprim) is an antibiotic used to treat ear infections, urinary tract and other infections. Includes Bactrim side effects, interactions and indications. Trimethoprim-sulfamethoxazole is an antibiotic used to treat various bacterial infections. 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] 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.