Relative potency of some neuromuscular blocking drugs in vivo and in vitro

The relative potencies of alcuronium, d-tubocurarine, gallamine, pancuronium and succinylcholine as neuromuscular blocking agents were tested in vivo (acute toxicity in mice) and in vitro (rat phrenic nerve-diaphragm preparation). In vivo, pancuronium was about 4 times more potent than alcuronium or d-tubocurarine, whose LD50-values were of the order of 2 X 10(-7) mol/kg. On a molar basis, succinylcholine was about 5 times less potent and gallamine about 20 times less potent than alcuronium or d-tubocurarine. In vitro, succinylcholine was as effective as d-tubocurarine and alcuronium. The IC50-values for these drugs were of the drugs were of the order of 2 X 10(-6)M. Pancuronium was about 2 times less potent and gallamine about 100 times less potent than the other three drugs in vitro. The in vivo-potencies correlate better than those obtained in vitro with observations from the clinical use of these muscle relaxants.