Effect of the injection site on the pharmacokinetics of procaine penicillin G in horses.

This research investigates the effect of different injection sites on the pharmacokinetics of procaine penicillin G in horses. The study shows that injecting the drug into the neck and biceps results in higher penicillin plasma peak concentration and bioavailability.

Study Methodology

• The study started by monitoring the effects of an intravenous injection of sodium penicillin G on five horses. The plasma penicillin concentrations were evaluated in this phase.
• The researchers then conducted a crossover experiment where they observed the variations in plasma penicillin concentrations in animals given procaine penicillin G through subcutaneous injections at one site, and intramuscular injections at four separate sites.

Main Findings

• The highest penicillin plasma peak concentration and bioavailability were observed when the drug was injected into the neck and biceps musculature of the horses. The term “bioavailability” refers to the fraction of an administered drug that reaches the systemic circulation and is available at the site of action to produce its effects.
• In contrast, injections in the gluteal muscle and in the subcutaneous sites resulted in similar, but lower and more persistent penicillin plasma concentrations. Moreover, the bioavailability of the drug was also found to be lower when injected at these sites, compared to the neck and biceps musculature.
• The pharmacokinetic data obtained after administering penicillin via the pectoral muscle route occupied an intermediate position between the above two scenarios. This means that injection in the pectoral muscle resulted in neither the highest nor the lowest penicillin plasma concentrations and bioavailability.

Therapeutic implications

• The study also discusses the therapeutic implications of the varying routes of administration with respect to treating hemolytic streptococcal infections. Hemolytic streptococcal infections are bacterial infections that can cause a variety of illnesses in horses, often requiring antibiotic treatment.
• The findings of this research could influence future practices for the administration of procaine penicillin G in horses. The choice of injection site might be affected, especially when treating hemolytic streptococcal infections.