The inhibition of cholinesterases by pancuronium.

Pancuronium causes a powerful and highly selective inhibition of human serum cholinesterase in vitro. The inhibition was studied in serum from 14 individuals of both sexes (5-60 years of age) with normal reactions to suxamethonium. Pancuronium, in a concentration of 2.3 x 10(-7) M, caused a 50% inhibition of the enzymatic hydrolysis of acetylcholine, when this substrate was present in a concentration of 10 x 10(-3) M. The same I50 value was also found for a commercial preparation of human serum cholinesterase. The inhibition was reversible and competitive in type. Pancuronium inhibition of the acetylcholinesterase in human red blood cells and from the electric eel was more than one thousand times weaker. Thus pancuronium is one of the most selective inhibitors of serum cholinesterase described so far. The in vivo activity of the serum cholinesterase in four patients receiving pancuronium 0.1 mg/kg decreased, during the first 3 min, by 60-80%, from the pre-induction value. After this a slow recovery occurred with 40% depression remaining at 45 min after the injection. The tachycardia produced by pancuronium may be related to this selective inhibition of serum cholinesterase. It is suggested that relaxants which selectively inhibit serum cholinesterase also selectively block the cardiac muscarinic receptors.