Antiperspirant activity of H1-histamine blockers as determined by a modified rat foot pad assay.

A method for inducing sweating in the rat via heat stress and without the use of general anesthetics is presented. Five commonly used H1-blocking antihistamines were evaluated in this model for their antiperspirant efficacy. The antihistamines evaluated and their ED50 values (micrograms base/pad) were as follows: phenindamine, 3.02; diphenhydramine, 3.25; chlorpheniramine, 3.12; tripelennamine, 4.91; and pyrilamine, 13.03. Atropine sulfate, injected into the foot pads, was also found to inhibit the sweat response. The response to atropine varied directly with dose. The ED50 was estimated to be 0.4 ng base/foot pad. No systemic effects or contralateral involvement were seen. The rat foot pad contains eccrine sweat glands that are innervated by sympathetic cholinergic fibers. This relationship is analogous to that in the eccrine sweat glands of man. The rat data suggest that antihistamines, possibly via an anticholinergic effect, may be useful as potential antiperspirants in man.