Elevated Plasma Procaine Concentrations after Administration of Procaine Penicillin G

Abstract

Plasma procaine concentrations were measured in 26 patients immediately after the intramuscular administration of 4.8 million units of procaine penicillin G for the treatment of gonorrhea. The values ranged from 3.6 to 11.0 μg per milliliter. Three different lots were also checked for the presence of free procaine in bottles stored at 4°C. The values ranged from 8.3 to 11.0 μg per milliliter and were increased with storage at room temperature or heating to 56°C. These levels probably account for the high frequency (0.9 per cent in our clinic population) of abnormal behavioral and neurologic reactions that occur after the administration of procaine penicillin G. Although 8.3 to 11.0 μg per milliliter free procaine was found in three different lots stored at 4°C, and though these values were increased at higher temperatures, these small amounts of free procaine in the mixture under different physical conditions were not a prerequisite to the inducement of the syndrome. Therefore, instantaneous liberation of toxic quantities of procaine from the mixture apparently occurs in vivo. (N Engl J Med 291:223–226, 1974)