Co-trimoxazole is a combination of two antibacterial medicines - a sulfonamide medicine called sulfamethoxazole, and trimethoprim. Although it has been prescribed widely for a range of infections in the past, it has very occasionally been associated with some serious side-effects. As a result, other antibiotics are now preferred to treat simple infections and co-trimoxazole is usually reserved for the treatment of more serious infections. In particular, it is prescribed for infections which can occur in people who have a problem with their immune systems. It works by killing the germs (bacteria) responsible for causing the infection.
This is a companion discussion topic for the original article at https://patient.info/medicine/co-trimoxazole-for-infection