Antimicrobial Agents and Chemotherapy.

Despite its relatively good acid stability, ampicillin is absorbed rather poorly from the gastro-intestinal tract, varying from 30 to 50% (8, 10, 12). One of the attempts to achieve better absorption resulted in the development of pivampicillin, the pivaloyloxymethyl ester of ampicillin, which is rapidly hydrolyzed to ampicillin in the body; 15 min after administration, more than 99% of the drug in the blood is present as ampicillin (18). The serum concentrations of ampicillin after oral administration of pivampicillin have been compared with those after ampicillin given by the oral route (1, 4, 6, 12, 15-17, 19, 20) or intramuscularly (3, 7, 13); only three of these studies were done in patients (6, 12, 13). The general impression obtained from these studies is that after equimolar doses the mean (peak) serum levels of ampicillin after orally administered pivampicillin are two to three times higher than those seen after orally administered ampicillin and are almost comparable with those after intramuscularly administered ampicillin. Several objections can be raised to most of these studies, however. (i) The amount of the drug absorbed in relation to the dose is difficult to evaluate. (ii) Most of the studies were done in healthy subjects. (iii) The individual variations in absorption, which are important in relation to therapy, were not taken sufficiently into consideration. A more recent study on the absorption of pivampicillin (10) gives better information about the amount of pivampicillin that is absorbed, but this investigation too was done in healthy subjects. In the present study the quantitative absorption of oral pivampicillin was compared with that of intravenously administered ampicillin in postoperative patients. MATERIALS AND METHODS