cotrimoxazoleEtymologyFrom co- + blend of trimethoprim + sulfamethoxazole.nounA sulfonamide antibacterial combination of trimethoprim and sulfamethoxazole, in the ratio of 1 to 5, used in the treatment of a variety of bacterial infections.“Because pediatricians are concerned that prolonged use of cotrimoxazole could lead to resistant malaria, they often stop the drug among AIDS patients when tests show significant improvement in the health of their immune system after antiretroviral therapy.”