DISPOSITION OF PENICILLIN-G SODIUM FOLLOWING INTRAVENOUS AND ORAL-ADMINISTRATION TO EQUIDAE

The present study was designed to determine and compare the plasma dis position and pharmacokinetics of penicillin G sodium following intrave nous (i.v.) administration to horses, ponies and donkeys. The plasma d isposition and pharmacokinetics of penicillin G was similar in horses, ponies and donkeys (elimination half-lives - 39.0, 27.3 and 31.5 min, respectively) and a dosage interval of 6-8 h would be suitable to tre at infections caused by susceptible bacteria. Although penicillin G wa s absorbed rapidly following nasopastric administration, the systemic availability was low (0.12-0.34%), therefore oral administration would be unsuitable for systemic antimicrobial therapy in the equine. The e limination of penicillin G into the gastrointestinal tract following i .v. administration and the absorption of penicillin G from the gastroi ntestinal tract following oral administration were studied in two poni es with cannulated caecal fistulas. A low concentration of penicillin G (less than or equal to 0.6 mu g ml(-1)) was measured in caecal liquo r following i.v. administration, however the risk of development of an timicrobial-associated colitis would be high following oral administra tion of penicillin G since high concentrations of drug (4.96-157.12 mu g ml(-1)) were measured in caecal liquor.