Magnitude, dose-requirement and mode of development of tachyphylaxis to suxamethonium in man.

Tachyphylaxis to suxamethonium infused at a constant rate was studied in 15 surgical patients under enflurane-nitrous oxide-oxygen anaesthesia. The compound electromyographic response of the adductor pollicis muscle to stimulation of the ulnar nerve was monitored. A short-lasting and a long-lasting nearly steady state were observed in Phase I and in Phase II, respectively, during both of which a constant infusion resulted in a constant block. Tachyphylaxis occurred during the transition of phases, beginning after infusion of 1.4 +/- 0.6 (SD) mg kg-1 of suxamethonium, and 36 +/- 14 (SD) minutes of exposure. Tachyphylaxis peaked after 2.6 +/- 1.3 (SD) mg kg-1, and 72 +/- 38 (SD) minutes of exposure. The maximum gain in neuromuscular transmission from the initial maintenance level of block as the result of tachyphylaxis was 53 +/- 24 (SD) % of the control. The results are thought to reconcile previously reported conflicting clinical observations on tachyphylaxis.