The classification of the myoneural blocking agents.

THE classification of myoneural blocking agents at present accepted at least in Great Britain, divides these drugs into two groups, viz. those which compete with acetylcholine and prevent its access to the muscle end plate, i.e. the competitive blockers, and those which themselves depolarize the end plate with the result that the normal depolarizer, acetylcholine, is no longer able to exert its physiological function. It is, however, admitted already on all sides that substances exist which are capable of blocking transmission across the myoneural junction, yet cannot be assigned to either of these groups. For the want of a better description drugs of this type are referred to as possessing a ' mixed ' action (Paton, 1953). The issue has become further complicated. For in order to explain some of the actions of decamethonium, the prototype of the depolarizing myoneural blockers, it has become necessary to postulate that this agent, while initially exerting its typical action, later exerts its paralysing activity by competing with acetylcholine (Zaimis, 1953). It therefore seems as if the classification of agents of this type into the accepted hard and fast groups is not satisfactory.