Organic compounds containing the group –SO2.NH2. The sulphonamides are amides of sulphonic acids. Many have antibacterial action and are also known as sulpha drugs, including sulphadiazine, NH2C6H4SO2–NHC4H3N2, sulphathiazole, NH2C6H4SO2NHC5H2NS, and several others. They act by preventing bacteria from reproducing and are used to treat a variety of bacterial infections, especially of the gut and urinary system.