The skeletal muscle response to the repeated administration of suxamethonium and its interaction with edrophonium in anaesthetised man.

Tetanic and single twitch contractions of the adductor pollicis muscle in man were recorded during repeated injections of suxamethonium (0.2 mg/kg or 0.1 mg/kg) every 15 minutes. 2 Tachyphylaxis to suxamethonium developed rapidly in every patient studied when single twitch contractions were observed but tetanic contractions later showed an increasingly prolonged recovery with repeated injections. 3 Edrophonium administered at the point of 50% recovery of the tetanic contractions in patients given suxamethonium (0.2 mg/kg) repeatedly first potentiated the blockade but when the tachyphylaxis had developed fully on the single twitch, usually after the third or fourth injection, the blockade of the tetanic contractions was reversed. 4 These findings indicate that the tachyphylaxis and the change in the nature of the blockade produced by suxamethonium in man take place at the same time and might be part of the same phenomenon.