Studies on dimethyl tubocurarine in anaesthetized man

Intravenous doses of 0.3 mg/kg dimethyl tubocurarine were required for consistent and adequate surgical relaxation in patients during nitrous oxide anaesthesia and produced virtually complete neuromuscular paralysis (96-100%) of the tetanic and twitch responses of the adductor pollicis muscle. The duration of action of the drug was prolonged--more than 3 h was required to attain 50% recovery from full neuromuscular paralysis. At this degree of recovery neostigmine was an effective antagonist. Determination of the tetanic tension ratios showed that tetanic fade developed during onset of paralysis and remained maximal until about 25% recovery of the tetanic contractions, when it disappeared raidly as recovery progressed. These doses caused no significant changes in arterial pressure and heart rate and this absence of cardiovascular side-effects is a desirable property of dimethyl tubocurarine. However, for many surgical procedures, an agent with a similar pharmacological profile but with a shorter action is desirable.