Stability of sulbactam/ampicillin in diluents for parenteral administration

Compatibility studies were conducted of sulbactam/ampicillin in infusion diluents that are reported to be compatible with ampicillin sodium. A high-performance liquid chromatographic system that simultaneously detects sulbactam and ampicillin was used to determine whether the infusion diluents and the conditions of use recommended for ampicillin sodium are applicable to sulbactam/ampicillin. The results show that the sulbactam/ampicillin preparation for parenteral administration is compatible with all diluents recommended for ampicillin sodium. In all diluents sulbactam was more stable than ampicillin. At the end of the reported use periods, the average retention value for sulbactam in the combination solutions was 96% (range, 91%-101%), whereas the average retention value for ampicillin in the same solutions was 90% (range, 84%-95%). The presence of sulbactam had no adverse effect on the stability of ampicillin. The average retention value for ampicillin alone in the same diluents was 92% (range, 82%-99%). The conditions of use for sulbactam/ampicillin in diluents for parenteral administration are unrestricted by the presence of sulbactam and are, in fact, governed by those of ampicillin sodium.