ABSTRACT
The beta lactam antibiotics include the penicillins and cephalosporins. Penicillin has the distinction of being the first clinically useful antibiotic. Since its first therapeutic trial in 1941, it has become the foundation on which many other semisynthetic penicillins have been based. All penicillins have as their basic structure a thiazolidine ring, a beta lactam ring, and variable side chains which account for the major differences in their chemical and pharmacological properties. Examples of widely utilized penicillins include the natural benzylpenicillin and phenoxymethylpenicillin produced by Penicillium, the benzylpenicillin ester, penethamate, as well as numerous semisynthetic analogues. The cephalosporins are structurally related to the penicillins, their mechanism of antimicrobial action is the same as penicillins. Antimicrobial activity is a function of the "generation" of the drug used. First-generation cephalosporins have activity primarily against Gram-positive organisms, while higher generation drugs have increasing activity against Gram-negative organisms with variable Gram-positive activity.
