noun
: any of a class of synthetic organic antibacterial usually crystalline drugs (as sulfadiazine or sulfathiazole) that are sulfonamides closely related chemically to sulfanilamide
the sulfa drugs are antibacterial agents, bacteriostatic rather than germicidal in action, which are used alone or in various combinations with each other or with antibiotics in the treatment of many types of infection such as those caused by β-hemolytic streptococci or pneumococci — M.E.Hultquist