Two-dose technique to create an individual dose-response curve for atracurium

While monitoring the thenar EMG response to ulnar nerve stimulation, the authors gave either 105, 150, 210, or 300 micrograms/kg of atracurium to 60 patients. The maximal neuromuscular responses were plotted on a log-probit paper. The individual second dose required to produce 95% neuromuscular block (NMB) was estimated from a graph drawn on the paper. The maximal response following this second dose was then plotted. The mean maximal response following the second atracurium dose was 95.5% (SD range, 92.6-97.4%) NMB. The two dose-response points thus acquired resulted in the individual two-dose dose-response curve. The ED50 and ED95 and slope of the two-dose dose-response curve were compared with the single-dose dose-response curve. The average ED50 and ED95 determined by the two-dose and the single-dose techniques were nearly identical [160 micrograms/kg (SD range, 126-201 micrograms/kg) vs. 164 micrograms/kg (SD range, 150-179 micrograms/kg) and 302 micrograms/kg (SD range, 251-363 micrograms/kg) vs. 336 micrograms/kg (SD range, 274-411 micrograms/kg) respectively]. Also, the slopes of the curves were similar [6.2 (SD range, 5.2-7.2) vs. 5.4 (SD range, 4.5-6.4) probit/log]. It is therefore possible to construct an individual dose-response curve for atracurium within 7-9 min and to determine individual pharmacodynamic characteristics of atracurium from this curve.