PHARMACOKINETICS, INTRAMUSCULAR BIOAVAILABILITY, AND BIOEQUIVALENCE OF AMOXICILLIN IN DONKEYS

The disposition kinetics of intravenously (i.v.) administered amoxycil lin sodium (10 mg/kg) was determined in four adult donkeys. The elimin ation half-life (t(1/2 beta)) of 47.3 +/- 5.1 min, the apparent volume of distribution (V-area) of 0.325 +/- 0.093 l/kg and the total body c learance (Cl-B) of 4.76 +/- 1.33 ml/min . kg were very close to the co rresponding values reported for the horse injected i.v. with amoxycill in sodium. It Nas evident that because of the rapid rate of drug elimi nation, limited distribution volume, and high clearance values, the i. v. injected amoxycillin sodium (10-20 mg/kg) was likely to result in p otentially therapeutic tissue concentrations for a short time (2-3 h) only. Three formulations of 15 % amoxycillin trihydrate suspension in oil were injected intramuscularly (i.m.) to each donkey at 10 mg/kg. D rug absorption was rapid and the elimination half-life (t(1/2el)) rang ed between 6 and 10 h. Mean peak serum amoxycillin concentrations (C-m ax) were, however, rather low (0.81-1.68 mu g/ml) and the i.m, bioavai lability was 25.8-45.1 % for the different formulations. Although the three formulations were considered to be intramuscularly bio-equivalen t and appeared to be well tolerated, it was estimated that multiple SI D (once daily) treatments ar 10-20 mg/kg could result in tissue concen trations of potential therapeutic value for the treatment of infection s caused by very susceptible pathogens only.