[Nontraditional beta-lactam antibiotics]

In recent years several beta-lactam derivatives have been obtained, which differ markedly from the traditional penicillins and cephalosporins, some of which have been introduced in the clinic. Clavulanic acid has an oxygen atom instead of sulfur but differs also markedly on C2 and C6. This inhibitor of penicillinase is used in association with amoxicillin and ticarcillin. Sulbactam and tazobactam are other beta-lactamase inhibitors, which are also used in association with penicillins. In the carbapenems sulfur is replaced by a carbon atom and a double bond is also present. Thienamycin, which is rather labile, has been transformed into a more stable product, imipenem, which is used in the treatment of infections with gram-positive and -negative bacteria. Other carbapenems are being studied. Several synthetic penems also present an interesting activity and may be used in medicine. Monobactams are monocyclic beta-lactams isolated from bacteria. By modification of the natural products aztreonam was obtained, a substance which is used in the treatment of infections with gram-negative bacteria. Other monobactams, prepared by total synthesis like aztreonam, are being studied.