Pharmacokinetics of penicillin G procaine versus penicillin G potassium and procaine hydrochloride in horses.

The research study compares the pharmacokinetics (how drugs are absorbed, distributed, metabolized, and excreted in the body) of penicillin G and procaine when administered to racehorses in two forms – as PGP (penicillin G procaine) and as a combination of penicillin G potassium with procaine hydrochloride (PH).

Methods

• The study involved treating six healthy adult mares with PGP (dosage 22,000 units of penicillin G per kilogram of body weight) and with penicillin G potassium and PH (dosages of 22,000 U/kg and 1.55 mg/kg, respectively).
• Both drugs were administered intramuscularly (i.m.). A minimum of three weeks was allowed between the two treatment courses to ensure complete elimination of the first drug before the second one was administered.
• Penicillin G and procaine concentrations in the plasma and urine of the horses were measured using high-pressure liquid chromatography, a technique used to analyze and separate compounds. This helped to determine the absorption, distribution, metabolism, and excretion of the drugs.

Results

• Median elimination half-lives of penicillin G were different for the two forms of the drug: 24.7 hours for PGP and 12.9 hours for penicillin G potassium.
• The concentration of penicillin G in the plasma, 24 hours after administration, was almost the same for penicillin G potassium and PH as it was for PGP.
• In terms of procaine elimination, the median phase half-life following PGP administration (15.6 hours) was significantly longer than that obtained after administering penicillin G potassium and PH (1 hour).

Conclusions

• The study’s results suggest that administration of penicillin G potassium leads to plasma concentrations of penicillin G comparable to those achieved with PGP, 24 hours post-administration.
• Procaine clearance from plasma, when administered as penicillin G potassium and PH, was significantly faster than when administered as PGP.