The absorption, distribution, and elimination (pharmacokinetics) of penicillin G in swine was evaluated in an exploratory study after administration by three routes in 6 pigs weighing approximately 32 pounds at the start of the study and 64 pounds by study completion. Intravenous administration of potassium penicillin G was used to establish a baseline serum concentration curve. The area under this curve could then be used to establish how available penicillin G would be by other injection methods (bioavailability). It was found that intramuscular injection of procaine penicillin G by a hypodermic needle resulted in essentially all of the drug being available to the animal (100% bioavailable). Injection of the same dose of procaine penicillin G by a needleless, air injection system resulted in an estimate of approximately 73% of the drug being available as compared to intramuscular injection by a hypodermic needle. This estimate is based on the average of 4 pigs for which adequate data was available for comparing the 2 non-intravenous methods within the same pig.
The pharmacokinetic data derived from this study will be valuable in supporting development of dosing recommendations for procaine penicillin G in swine by the Veterinary Antimicrobial Decision Support (VADS) System. This system is being developed to support veterinarians in making antimicrobial use decisions in food animals.
The comparative bioavailability data from this study indicate that needless, air injection systems may differ in the amount of drug that becomes available to the animal, possibly requiring a dose adjustment. The relative bioavailability of the air injection system appears adequate to support further investigation in light of the advantages of reducing needle use in swine. A larger study is necessary to confirm and more accurately characterize the differences in pharmacokinetics and to calculate possible changes in dosing regimens and withdrawal times.
