The effect of phenylbutazone on the plasma disposition of penicillin G in the horse.

This research studies the interaction between phenylbutazone and penicillin in horses, showing that when administered together, they increase the plasma concentration of penicillin, likely because the drug’s distribution into tissues is reduced.

Research Methodology

• The study began with a pilot involving two ponies. The ponies were administered procaine penicillin intramuscularly. Consecutively, phenylbutazone was administered, and researchers measured the plasma concentrations of penicillin.
• The study was further expanded to include two different trials, each involving five horses. In both trials, sodium penicillin was administered intravenously and procaine penicillin was administered intramuscularly. Phenylbutazone was administered alongside the penicillin in both cases.

Findings

• The study found that when phenylbutazone was given at the same time as penicillin, the plasma concentrations of penicillin were higher. This was true for both the intramuscular and intravenous administration of penicillin.
• The pharmacokinetic parameters were analyzed to discern the cause of this increase in plasma concentration. The underlying reason seems to be a reduction in peripheral distribution, meaning that the penicillin did not diffuse into the tissues as much when phenylbutazone was also given.

Implications

• The findings of this study may have significant implications for the use of penicillin in veterinary medicine, specifically in horses. It suggests that the concurrent use of penicillin and phenylbutazone could potentially increase the effectiveness of penicillin due to increased concentration in the plasma.
• However, it is also important to consider that reduced tissue penetration could potentially limit the areas where the drug can take effect. Further research would be needed to fully understand the implications of this combination of drugs.