[Propanidid as an antagonist: competitive inhibitor of neuromuscular plaque acetylcholinesterase].

Propanidid is a competitive inhibitor not only of serum cholinesterase, but of neuromuscular plaque and brain acetylcholinesterase also. The I50 of plaque acetylcholinesterase occurs at much higher concentrations of anaesthetic than for serum enzyme, this may depend on the environmental conditions under which propanidide has to act, or on acetylcholinesterase's high degree of specificity by comparison with pseudocholinesterase. Succinylcholine also inhibits serum cholinesterase but not plaque enzyme. With respect to the serum enzyme, the inhibition curve of the two drugs combined is similar to that of propanidide alone. The prolongation of apnoea observed during propanidide-induced anaesthesia, when succinylcholine is administered, does not appear to be due to diminution of serum cholinesterase activity but rather to interference of the two other drugs with neuromuscular transmission.