The Cephalosporins I. CHEMISTRY AND MECHANISM OF ACTION Cephalosporins are b-lactam antibiotics that differ from the penicillins in that the B ring is a 6- membered dihydrothiazine ring. Variations among the cephalosporins are made on either the acyl side chain at the 7-position to change antibacterial activity or at the 3-position to alter the pharmacokinetic profile. Cephalosporin C was first isolated in 1948 by Dr. Abraham from a fungus, Cephalosporium acremonium, collected in seawater near a sewage outlet in Sardinia by Professor Guiseppe Brotzu in 1945. 1 2 3 General structure of the Cephalosporins acyl side chain dihydrothiazine ring b-lactam ring O C H C N S COOH O R2 R3 R1 N • Similar mechanism of action to penicillins. • Bind to penicillin binding proteins (transpeptidases, endopeptidases, and carboxypeptidases) and inhibit cell wall biosynthesis in both Gm + and Gm – bacteria. • However, degree and extent of binding to different PBPs may be different for the cephalosporins than for penicillins. For example, cephalothin causes lysis of Staph. aureus, whereas cephalexin produces long filamentous forms in E. coli. • In general, cephalosporins are less susceptible to b-lactamases compared to penicillins
Posted on: Mon, 10 Mar 2014 09:30:21 +0000
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