Role of cephamycins in obstetrics and gynecology. Infections of the female upper genital tract are usually polymicrobic, often involving mixed aerobic (facultative) and anaerobic bacteria. Optimal therapy provides coverage against aerobes (both gram positive and gram negative and especially the Enterobacteriaceae) and anaerobes (especially the beta-lactamase-producing gram-negative species, such as Bacteroides). A variety of antibiotics provide the broad spectrum of activity needed for these infections, including clindamycin plus an aminoglycoside, cephalosporins and cephamycins, imipenem, extended-spectrum penicillins and the beta-lactam agents combined with a beta-lactamase inhibitor. The cephamycins--cefoxitin, cefotetan and cefmetazole--have been shown to have a high rate of clinical efficacy and bacteriologic response. The cephalosporins are usually used for prophylaxis at the time of obstetric and gynecologic surgery. The cephamycins have recently undergone extensive evaluation for prophylaxis and have demonstrated comparable microbiologic and clinical efficacy. A pharmacokinetic comparison of cefoxitin, cefotetan and cefmetazole points to cefmetazole as a cost-effective alternative to cefoxitin and cefotetan for both prophylaxis and treatment of pelvic infections. 