THE EFFECT OF CHOLINESTERASE INHIBITORS ON THE TOXICITY OF PROCAINE IN MICE

¹ Department of Pharmacology, The University of Chicago, Chicago, Illinois

1. Four cholinesterase inhibitors and one non-esterase inhibiting parasympatthetic stimulant were tested for their effect on intravenous procaine toxicity in mice premedicated with the drugs.

2. Physostigmine and DFP showed significant protective effects, increasing the LD₅₀ of procaine 23 and 16 per cent, respectively.

3. Neostigmine and carbamic acid, N,N-dimethyl-4-dimethylamino-3-isopropyiphenyl ester, methiodide increased the susceptibility of mice to the toxic action of intravenous procaine, lowering the LD₅₀ 35 and 22 per cent, respectively.

4. Methacholine had no statistically significant effect on the toxicity of procaine.

5. These results indicate that the reputed antiprocainesterase activity of the cholinesterase inhibitors probably does not influence the toxicity of intravenous procaine in mice, and that other factors must be considered to explain the influence which these agents were seen to exert on procaine toxicity.