n. any one of a group of semisynthetic *beta-lactam antibiotics, derived from the mould Cephalosporium, which are effective against a wide range of microorganisms and are therefore used in a variety of infections. The older (first-generation) cephalosporins include *cefadroxil and *cefalexin; more recent (second-generation) drugs include *cefaclor and *cefuroxime. Third-generation cephalosporins, such as *ceftazidime, cefotaxime, and ceftriaxone, have greater activity against Gram-negative bacteria. Cross-sensitivity with penicillin may occur and the principal side-effects are allergic reactions and irritation of the digestive tract.