Some Pharmacological and Toxicological Properties of a New Long‐Acting Local Analgesic, Lac‐43 (Marcaine®), in Comparison With Mepivacaine and Tetracaine

SUMMARY The toxicological and pharmacological properties of mepivacaine, LAC‐43 (Marcain®)—a new local analgesic—and tetracaine were studied in experiments on animals and man using “classical” test methods. The experiments were performed by the “blind” technique; whenever possible, the results were subjected to statistical analysis and compared with those published by other investigators. LAC‐43, which is chemically closely related to mepivacaine, is more similar to tetracaine as regards its local analgesic and toxicological potencies. Thus, the acute toxicity in mice, guinea pigs and rabbits in different routes of application is about the same for LAC‐43 and tetracaine and roughly 4 times higher than that of mepivacaine. Furthermore, LAC‐43 and tetracaine have the same tissue toxicity—about 6 times higher than that of mepivacaine, but LAC‐43 has a lower cumulative and infusion toxicity relatively to mepivacaine and absolutely to tetracaine. In infiltration and conduction analgesia, LAC‐43 and tetracaine are about 3 times more potent than mepivacaine, and in surface analgesia both drugs are still more potent than mepivacaine, tetracaine being the most active. In spite of being an amide, LAC‐43 has shown evidence of being rapidly metabolised, and as the clinical experiments so far published have given promising results, it should be worth while to subject this new local analgesic drug to thorough investigations.