Pharmacology of procaine in the horse: a preliminary report.

The research investigated the pharmacological effects of procaine hydrochloride in Thoroughbred mares, outlining its impact on the central nervous system, plasma concentrations, half-life, and reaction with plasma esterases.

Research Context

• The study is grounded in the context of exploring the pharmacological properties of procaine hydrochloride when administered to Thoroughbred mares. Procaine is a local anesthetic drug that’s often used in various medical and veterinary procedures.

Effects on the Central Nervous System

• When Thoroughbred mares were rapidly injected with 1 gram of procaine hydrochloride, the mares displayed varying signs of central nervous system excitation for up to 4 minutes. The central nervous system excitation implies that the drug stirred a response in the nervous system, possibly apparent through noticeable behavior changes.

Procaine Plasma Concentrations and Half-Life

• The plasma concentrations of procaine were also variable and lasted only for a short period. The half-life of procaine in the horse’s system was found to be approximately 25 minutes. The plasma half-life of a drug refers to how long it takes for the concentration of the drug in the bloodstream to reduce by half.

Procaine Hydrolysis

• In vitro, which means outside the living body, typically in a controlled lab setting, it was observed that plasma from freshly collected equine blood hydrolyzed procaine with a half-life of approximately 7.5 minutes. Hydrolysis is a chemical reaction where a compound is broken down by water, which in this case, separated procaine into its constituent elements.

Interaction with Plasma Esterases and Penicillin

• It was found that the hydrolysis was primarily due to the action of plasma esterases, which are enzymes that break down esters into an acid and an alcohol in a chemical reaction with water.
• Interestingly, the research also examined the interaction of procaine with penicillin, a commonly used antibiotic. It was found that whether penicillin was added free or complexed as procaine-penicillin, it did not protect procaine against hydrolysis by these plasma esterases at a neutral pH of 7.4. This suggests that when mixed with penicillin, procaine can still be broken down by the body’s enzymes without the penicillin playing a protective role against such enzymatic action.