Pharmacokinetics of intravenous procaine infusion in humans

Pharmacokinetic data during and following the continuous intravenous infusion of procaine are lacking. We studied 12 women undergoing hysterectomy during N2O-O2 and narcotic anesthesia. A constant infusion of 2% procaine was administered at a rate of 1 mg/kg/min to six patients (group I) and at a rate of 1.5 mg/kg/min to the other six (group II). Procaine plasma levels were determined by flame ionization gas-liquid chromatography. Using a two-compartment pharmacokinetic model, disposition kinetics were studied. Steady-state plasma levels were achieved within 20 to 30 minutes after commencement of the infusion. Following termination of the infusion the drug disappeared with a distribution half-life (t1/2 alpha) of 2.49 +/- 0.36 minutes and an elimination half-life (t1/2 beta) of 7.69 +/- 0.99 minutes at both infusion rates. In group I, the fraction of drug in the central compartment was 65%, the volume of distribution at steady-state was 0.79 +/- 0.14 L/kg, and total body clearance 0.08 +/- 0.01 L/kg/min. In group II, the fraction of drug in the central compartment was 82%, the volume of distribution at steady-state 0.34 +/- 0.07 L/kg, and the total body clearance 0.04 +/- 0.01 L/kg/min. These data indicate that procaine is a drug of limited distribution and tissue uptake with a short duration of action.