Oral bioavailability of pivampicillin in foals at different ages

The plasma disposition of ampicillin after intravenous administration at a dose rate of 15 mg/kg was studied in six healthy, 1-month-old foals. The oral bioavailability of pivampicillin was determined in the same foals at four ages, ranging from 11 days to 4 months. Pivampicillin was administered orally at a dose rate of 19.9 mg/kg, which is equivalent on a molecular basis to 15 mg/kg ampicillin. Ampicillin concentrations in plasma were determined up to 12 hours after administration. After intravenous administration, the mean distribution and elimination half-lives of ampicillin were 0.121 and 0.624 h, respectively. The volume of distribution (Vss) appeared to be 0.334 l/kg. Orally administered pivampicillin was rapidly absorbed in all age groups, producing mean peak plasma concentrations of 3.83 to 5.69 micrograms/ml 1 h after administration. The mean bioavailability of pivampicillin in the different age groups ranged from 39.4 to 52.9%. There was no statistically significant difference in peak plasma concentration or bioavailability between the age groups. It is concluded that pivampicillin at a dose rate of 19.9 mg/kg orally gives satisfactory plasma concentrations in foals of all ages.