To the Editor:-In the September 1996 issue of the journal, CN Sang et al. reported on the allodynia and hyperalgesia produced by injection of capsaicin. [1] In their experiments, volunteers received radial or ulnar nerve blocks with a preparation of capsaicin. One wonders about the solution in which capsaicin was used. The reason for this query is that the OTC preparation of capsaicin known as Zostrix is an emollient containing benzyl alcohol, cetyl alcohol, etc. As reported by Duncan and Jarvis in 1943, [2] benzyl alcohol in 5–10% concentrations destroys peripheral nerve fibers. This is the reason for prolongation of block in anesthetic mixtures in oily media. We rediscovered this phenomenon in 1947 in an attempt to prolong sympathetic nerve block by using bromsalizol in polyethylene glycol. [3] Bromsalizol is a derivative of benzyl alcohol. Could the results achieved by Sang et al. be related to some substance in solution, perhaps benzyl alcohol?

Leroy D. Vandam, M.D.

Department of Anesthesia; Brigham and Women's Hospital; Boston, Massachusetts 02115

(Accepted for publication April 10, 1997.)

Sang CN, Gracely RH, Max MB, et al: Capsaicin-evoked mechanical allodynia and hyperalgesia cross nerve territories. Evidence for a central mechanism. Anesthesiology 1996; 85:491-6.
Duncan DH, Jarvis WH: Comparison of the action on nerve fibers of certain anesthetic mixtures and substances in oil. Anesthesiology 1943; 4:465-74.
Harmel H, Vandam LD, Lamont A: An attempt to prolong sympathetic block with bromsalizol in polyethyleneglycol. Anesthesiology 1947; 8:266-9.