Cephalosporins: rationale for clinical use.

Cephalosporins, the most widely used class of antibiotics, are more resistant than penicillins to inactivation by beta-lactamases. Based on their spectrum of activity against gram-negative bacteria, cephalosporins are classified into three generations. The generation classification, however, does not correlate with activity against gram-positive bacteria or anaerobes. First-generation cephalosporins have a narrow gram-negative spectrum but are most active against gram-positive bacteria, particularly Staphylococcus aureus. Third-generation compounds have excellent activity against gram-negative bacteria. The cephamycins, a second-generation subgroup that includes cefoxitin, cefotetan and cefmetazole, have the best activity against anaerobes.