The neuromuscular blocking action of suxamethonium following intravenous and intramuscular administration

In 35 anesthetized adult patients the neuromuscular blocking effect of suxamethonium (0.8-2.4 mg X kg-1) following i.v. or i.m. administration was studied by means of mechanomyograms of the hand muscles after electrical stimulation of the ulnar nerve (0.2 Hz, 100-120 volts, 0.2 ms). Compared with i.v. suxamethonium (= 1.0) the myoneural blocking activity of i.m. suxamethonium was less effective (0.128), the rate of onset slower (0.174), and the duration of action longer (1.4 to 1.7). According to the dose-response relationship, suxamethonium 3.0-4.0 mg X kg-1 should be administered i.m. to achieve complete neuromuscular blockade.