A COMPARISON OF NINE LOCAL ANESTHETICS

¹ Department of Pharmacology, University of Toronto

1. L.D. 50 values for procaine, metycaine, monocaine, naphthocaine, butacaine, octacaine, cocaine, pontocaine and nupercaine administered intraperitoneally in white mice, decrease in magnitude in the order given. Epinephrine hydrochloride in solution with each anesthetic increases the systemic toxicity of procaine and metycaine and decreases the toxicity of pontocaine and nupercaine significantly, but has no effect on the toxicity of the 5 other drugs tested.

2. Tissue toxicity in guinea pigs, as measured by intradermal injection, does not closely parallel systemic toxicity, and the spread of tissue toxicities is considerably greater. The measurement of skin toxicity is suggested as a basis for estimating relative toxicity for nerve block in dentistry and other uses involving small volumes of local anesthetic.

3. E.C. 50 values for infiltration anesthesia have been determined in guinea pigs by intradermal injections of each anesthetic together with epinephrine hydrochloride (1:100,000).

4. E.C. 50 values for surface anesthesia of the guinea pig cornea have been determined.

5. Relative Rating Indices are defined and estimated for infiltration anesthesia, localized block anesthesia, corneal anesthesia and mucous surface anesthesia.

6. Two relatively new drugs, naphthocaine and octacaine, with high Relative Ratings for all four types of anesthesia, appear to be worthy of further clinical study.