Curare modification of suxamethonium blockade

Tubocurare (0.125 mg.kg-1 or 0.25 mg.kg-1) was injected 10 s before 1 mg.kg-1 suxamethonium in patients anaesthetised with enflurane 1-1.5%. Measurement of electromyographic response was recorded using a 0.2 Hz train-of-four every 20 s. The modified blocks were slower in onset, of lesser intensity, and of shorter duration than that of suxamethonium alone, but were much closer to those of suxamethonium than of tubocurare. However, the train-of-four fade observed during onset of the modified blocks were similar to that of their tubocurare controls and significantly different from the suxamethonium group. We conclude that effective amounts of tubocurare are present in the neuromuscular junction within the 30 s following intravenous injection of the drugs, and this affects the onset of action of the suxamethonium block. The presence of train-of-four fade during a predominantly agonist block is difficult to explain on the basis of diminished acetylcholine release and a postsynaptic site of action of suxamethonium.