Serum concentrations of penicillin in the horse after administration of a variety of penicillin preparations.

Abstract

Twelve geldings were used to evaluate serum levels of penicillin following the intravenous (iv) and intramuscular (im) injection of benzylpenicillin, im procaine penicillin and im fortified benzathine penicillin, at a variety of dose rates. Blood samples were collected up to 7 h after iv and im benzylpenicillin, up to benzathine penicillin. Results were analysed using an analysis of variance and regression analyses were used to calculate the time taken for the serum penicillin concentration to decline to 0.5 micrograms/ml. As a result of the experiments the following dosage regimes could be recommended for each drug. Benzylpenicillin should be administered im at a dose rate of 10,000 iu/kg at the commencement of treatment. Procaine penicillin should be injected at a dose rate of 15,000 iu/kg every 12 h or 30,000 iu/kg every 24 h. In serious infections 10,000 iu/kg of benzylpenicillin im should be used concomitantly to begin therapy. Fortified benzathine penicillin appears to have little value for antimicrobial therapy in the horse.