Pharmacokinetics of an ampicillin-sulbactam combination after intravenous and intramuscular administration to neonatal calves

The bioavailability after i.m. injection was high and similar for both drugs (70.31 ± 0.2% for ampicillin and 68.62 ± 4.44% for sulbactam). The mean peak plasma concentrations of ampicillin and sulbactam were reached at similar times (0.47 ± 0.02 and 0.72 ± 0.01 h, respectively) and peak concentrations were also similar but not proportional to the dose administered (17.88 ± 0.91 mg/L of ampicillin and 12.92 ± 0.79 mg/L of sulbactam). Both drugs had similar pharmacokinetic behaviour after i.m. administration. Since the plasma concentrations of sulbactam were consistently higher during the elimination phase of their disposition, consideration could be given to formulating the ampicillin-sulbactam combination in a ratio higher than 2:1.