Pharmacology of procaine in the horse: a preliminary report.

Rapid intravenous injection of 1 g of procaine hydrochloride in Thoroughbred mares produced variable signs of central nervous system excitation for as long as 4 minutes. Plasma concentrations of procaine were similarly variable and transient, decreasing with a half-life of approximately 25 minutes. In vitro, plasma from freshly collected equine blood hydrolyzed procaine with a half-life of approximately 7.5 minutes. This hydrolysis was apparently due to plasma esterases. Penicillin, when added free or complexed as procaine-penicillin, did not protect procaine against hydrolysis by these plasma esterases at pH 7.4.