The Tetracaine Flare

Abstract

Summary

1. Tetracaine hydrochloride, injected intradermally, produces a histaminelike flare which can be blocked hy procaine hydrochloride, 2. On the isolated nerve, tetracaine has much less effect on conduction in C fibers with respect to its effect on A fibers than is the case with procaine. (Preliminary experiments.) 3. In the human skin, tetracaine has much less effect on the threshold for “slow” pain with respect to its effect on “fast” pain than is the case with procaine. 4. These observations suggest that the dare is mediated over C fibers. Tetracaine produces a flare 1) by causing irritation. 2) by failing to block completely the C fibers. 5. The differences in action on conduction of tetracaine and procaine are noted, but no explanation for these differences is available.