An Alternate Method for Estimating the Dose-Response Relationships of Neuromuscular Blocking Drugs

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Abstract
Slopes of the dose-response relationships for all available neuromuscular blocking drugs appear to be essentially parallel and to approximate a log-dose/logit value of 4.75. We tested the possibility of estimating both 50% effective dose (ED50) and 95% effective dose (ED95) values from a single dose-response data point when that slope is postulated. We compared the ED50 and ED95 values of rocuronium and succinylcholine calculated by using traditional log-dose/logit regression analysis with the same values obtained by averaging individual estimates of potency as determined by using the Hill equation. After the induction of anesthesia (propofol/alfentanil), tracheal intubation was accomplished without the administration of neuromuscular blocking drugs. Anesthesia was maintained with nitrous oxide and propofol. The evoked electromyographic response to 0.10-Hz single stimuli was continuously recorded. After baseline stabilization, a single IV bolus of succinylcholine (0.08–0.26 mg/kg, n = 50) or rocuronium (0.13–0.30 mg/kg, n = 40) was administered and the peak effect noted. By using log-dose/logit regression analysis, we calculated ED50 and ED95 values for rocuronium of 0.17 and 0.33 mg/kg and 0.14 and 0.27 mg/kg for succinylcholine. When potency was calculated from the Hill equation, the resultant ED50 and ED95 values did not differ by more than ±4% from those obtained by using regression analysis. Averaging of single-dose estimates of neuromuscular potency provides a useful adjunct and reasonable alternative to conventional regression analysis. Averaging of single-dose estimates of neuromuscular potency provides a useful adjunct and reasonable alternative to conventional regression analysis.