Sulbactam, a new beta-lactamase inhibitor, has pharmacokinetic characteristics in humans similar to those of ampicillin and amoxicillin. Its half-life in humans is approximately 1 h. In a two-compartment pharmacokinetic model, the apparent volume of distribution for the central compartment is approximately 12 liters, and half of the dose is found in the central compartment in the postdistributive phase. Approximately 75% of a parenteral dose is excreted unchanged in urine. The coadministration of sulbactam with ampicillin, penicillin G, or cefoperazone has essentially no effect upon the kinetics of either the beta-lactam antibiotic or sulbactam.

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A quantitative turbidimetric bioassay has been developed for carbenicillin with the use of a strain of Escherichia coli. The assay is relatively specific for carbenicillin and is not affected by 10% (wt/wt) benzylpenicillin. It has been demonstrated to be more precise than the plate diffusion assay. Since it is readily automated, it is also faster and less expensive. The influence of pH, time, and extent of growth on the assay has been evaluated.

A quantitative cylinder plate bioassay for sulbactam has been developed which can detect concentrations as low as 0.01 ,ug/g in bovine muscle, fat, kidney, and liver tissues. This procedure may also be applicable to human tissues and fluids. In addition to the improved sensitivity, this method differs from all previously described systems because it is based on inhibition by sulbactam of a cell-free I-lactamase incorporated in the assay agar. The assay is unaffected by the presence of ampicillin even at concentrations 10 times that of the sulbactam concentration. This report describes the analytical technique as well as the accuracy and precision of the method. The assay can be applied to tissue depletion studies.Sulbactam 899) is a new semisynthetic ,-lactamase inhibitor which by itself has very weak antibacterial activity (7). When used in combination with ,-lactam antibiotics, it extends their in vitro and in vivo antibacterial spectra (4).Several microbiological assay methods have been described for sulbactam in body fluids. English et al. (4) used Comamonas terrigena ATCC 8461 as the assay organism, with a detection limit of approximately 0.5 ,ug/ml. This assay could not be performed in the presence of ampicillin because of ampicillin-induced interference. Therefore, removal of the ampicillin from the sample was necessary before assay. Although Brown et al. (1) and, later, Wright and Wise (9) could assay sulbactam in the presence of ampicillin by using Escherichia coli ATCC 43822, the detection limit was only 0.5 ,ug/ml. By using whole cells of Pasteurella haemolytica