The action and interaction of diphenhydramine (Benadryl) hydrochloride at the neuromuscular junction

Abstract

A. ABDEL-AZIZ and N. BAKRY. The action and interaction of diphenhydramine (Bendryl) hydrochloride at the neuromuscular function, European J. Pharmacol. 22 (1973) 169–174. Diphenhydramine(Benadryl) · HCl, in concentrations of 5–30 μg/ml augmented indirect muscle twitches of the rat phrenic nerve-diaphragm preparation, but in higher concentrations (40–100 μg/ml) resulted in failure of neuromuseular transmission which was usually preceded by transient augmentation of twitches. This blockade was not antagonized by neostigmine. The drug had an anti-tetanic action, reduced post-tetanic potentiation and blocked augmentation of indirect muscle twitches caused by neostigmine on the rat phrenic nerve-diaphragm preparation and on the cat tibialis. Diphenhydramine reduced the action of acetylcholine on the frog rectus muscle. In the rat phrenic nerve-diaphragm preparation, depending on the concentrations of the drugs used, interaction of diphen-hydramine with thiopentone, pentobarbital and phenobaibitone, resulted in either augmentation of muscle twitches or neuromuseular blockade. In the cat tibialis, diphenhydramine antagonized the biphasic actions of decamethonium and succinylcholine, while in the case of the rat and human phrenic nerve-diaphragm preparations, it potentiated the blockade caused by decamcthonium.