SummaryWe compared the dose-response relationships of cisatracurium, mivacurium, atracurium, vecuronium and rocuronium and examined the interactions of cisatracurium with mivacurium, atracurium, vecuronium and rocuronium in humans by isobolographic and fractional analyses. We studied 180 adult patients during nitrous oxide-fentanyl-propofol anaesthesia. Neuromuscular block was monitored using mechanomyography to detect the twitch response of the ulnar nerve at the wrist. The dose-response curves were determined by probit analysis. The calculated ED 50 values and their 95% confidence intervals were 40.9 (38.1-43.7), 49.8 (47.0-52.6), 187.2 (175.1-199.3), 36.6 (34.7-38.5) and 136.4 (129.2-143.6) mg.kg ¹1 for cisatracurium, mivacurium, atracurium, vecuronium and rocuronium, respectively. Corresponding ED 95 values were 57.6 (53.5-61.7), 91.8 (88.1-95.5), 253.1 (238.9-267.3), 52.9 (49.1-56.7) and 288.7 (276.2-301.2) mg.kg ¹1 , respectively. The interaction between cisatracurium and mivacurium, vecuronium or rocuronium was found to be synergistic, but the interaction between cisatracurium and atracurium was found to be additive. Synergy between cisatracurium and vecuronium or rocuronium was greater than between cisatracurium and mivacurium.

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We have compared the dose-response relationships of suxamethonium, mivacurium and atracurium and examined the interactions of suxamethonium with mivacurium or atracurium in humans by isobolographic analysis. We studied 100 adult patients during fentanyl and thiopentone anaesthesia. Neuromuscular function was monitored using a Myograph 2000 (Biometer Co., Odense, Denmark). The dose-response curves were determined by probit analysis. Isobolographic and fractional analyses were used to assess quantitatively the combined effect of equipotent doses of suxamethonium, mivacurium and atracurium and to define the type of interaction between suxamethonium and mivacurium or atracurium. The ED50 values for suxamethonium, mivacurium and atracurium were 198.8 (95% confidence interval 190.7-206.9), 48.6 (45.4-51.8) and 202.1 (197.9-206.2) mg kg-1, respectively. Isobolographic and fractional analyses of the suxamethonium-mivacurium and suxamethonium-atracurium combinations demonstrated antagonistic interactions.

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