Any of a family of antibiotics related to penicillin, discovered in 1953; an important member of this group was synthesized by Woodward in 1966. Several cephalosporins are used clinically (cephalothin, cephaloridine, and cephalexin). The molecule contains a fused β-lactam-dihydrothiazine ring system with an N-acyl side chain and an acetoxy group attached to the dihydrothiazine ring. The formula for cephalosporin (C) is C16H21N3O8S. Cephalosporins are reported to be free from the allergic reactions common with penicillin. Development of new cephalosporin derivatives is being actively pursued.See Penicillin; Antibiotic.