The pharmacokinetics of prophylactic antibiotics administered by intraoperative irrigation at the time of cesarean section

Thirty patients at term undergoing cesarean section received intraoperative irrigation with either cefamandole, cephalothin, or ampicillin to prevent postoperative infection. Serum drug levels were measured at 15, 60 and 120 minutes after completion of irrigation. Serum levels at each sampling interval were highest for cefamandole and lowest for cephalothin. Less than 2% of the total drug dose was excreted in the urine during the first 2 postoperative hours. In most patients, maximum serum antibiotic concentrations exceeded minimal inhibitory concentrations for several recognized pelvic pathogens. It is concluded that the mechanism of action of intraoperative irrigation may in part be due to systemic absorption of antibiotic and not simply to a local effect on the endometrium. Moreover, the degree of systemic absorption may be sufficient to cause allergic drug reactions and to exert selective pressures for the emergence of drug-resistant microorganisms.