Anticonvulsant actions of anticholinergic drugs in soman poisoning

The acute effects of the organophosphorus cholinesterase inhibitor soman include hypersecretions, convulsions, and death. The purpose of this study was to evaluate the anticholinergic compounds aprophen, atropine sulfate, azaprophen, benactyzine, benztropine, biperiden, scopolamine HBr, and trihexyphenidyl for their efficacy in preventing soman-induced hypersecretions and convulsions. Male rats were injected with the oxime HI-6 (125 mg/kg, i.p.), to increase survival time, along with various intramuscular doses of the anticholinergics 30 min prior to a dose of soman (180 micrograms/kg, s.c.; equivalent to 1.6 x the median lethal dose) that produced 100% convulsions. Signs of intoxication as well as the time-to-onset of convulsions were observed. The calculated anticonvulsant median effective dose values were 0.18, 0.33, 0.36, 0.55, 2.17, 2.30, 2.45, and 31.09 mumol/kg for scopolamine HBr, biperiden, trihexyphenidyl, benactyzine, benztropine, azaprophen, aprophen, and atropine sulfate, respectively. The same rank order of potency for inhibition of hypersecretions among these compounds was observed. Parallel studies with quaternary analogs of atropine sulfate and scopolamine HBr demonstrated, however, that these charged compounds afford no protection against soman-induced hypersecretions and convulsions. The results indicate that tertiary anticholinergic compounds afford protection against soman-induced convulsions and hypersecretions and that the beneficial anticonvulsant effects are mediated through the central cholinergic system. Excitatory amino acid neurotransmitter systems may be involved in the effectiveness of these compounds.