Bioavailability and pharmacokinetics of ampicillin and amoxycillin from tablets, capsules and long-acting preparations in the homing pigeon (Columba livia)

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Abstract
Three ampicillin and three amoxycillin formulations (tablets and capsules, administered orally, and oily suspensions, injected intramuscularly (i.m.) and subcutaneously (s.c.)) were studied in twenty adult homing pigeons (Columba livia). Bioavailability, pharmacokinetics and recovery were determined for each product and administration route. A standard dose of 50 mg/pigeon or 100 mg/kg was used in each study. The mean availability calculated for each of these preparations was 7% for ampicillin anhydrate tablets, 22% for amoxycillin trihydrate tablets, 17% for ampicillin trihydrate capsules, 67% for amoxycillin trihydrate capsules, 46% for ampicillin oily suspension i.m., 67% for amoxycillin oily suspension i.m. and 43% for amoxycillin oily suspension s.c. The blood concentration-time curves for the tablets were very scattered, which was far less the case for the capsules. The maximum blood concentration (Cmax) for amoxycillin was twice as high as for ampicillin. The Cmax resulting from the oily suspensions administered i.m. were low (4.35 .+-. 1.05 and 5.04 .+-. 1.36 mg/l, for ampicillin and amoxycillin, respectively). The Tmax for ampicillin was 10 h and for amoxycillin it was 0.9 h after administration. Both curves showed biphasic absorption, the initial peak representing an absorption and a distribution phase and the second part reflecting the ''depot-nature'' of the drug. After the s.c. administration of the amoxycillin oily suspension the same pattern was found, but the Cmax, which was found at 2.13 .+-. 1.03 h after administration, was low (2.81 .+-. 0.68 mg/l). The duration of potentially therapeutic blood concentrations after administration of each preparation for the MIC levels of 0.5 and 2.5 mg/l are also presented.