Atracurium and vecuronium: effect of dose on the time of onset

The time intervals measured from the administration of either atracurium or vecuronium to maximum or 95% neuromuscular blockade (Tmax) were compared in 70 patients using the evoked compound action potential of the adductor pollicis muscle. Equipotent doses, calculated from the relationship between dose and response for both drugs obtained in an earlier study, were compared. The doses of atracurium and vecuronium ranged from 0.135 to 0.5 mg kg-1 and from 0.02 to 0.1 mg kg-1, respectively. The dose range for both drugs included the ED50, ED95 and the dose required to produce 100% blockade (ED"100"). No significant changes in mean Tmax occurred for doses of atracurium in the range 0.135-0.2 mg kg-1 and in the range 0.24-0.5 mg kg-1. Similarly, no change in Tmax occurred at doses of vecuronium in the range 0.02-0.05 mg kg-1 and 0.06-0.1 mg kg-1. Tmax changed significantly in the dose ranges atracurium 0.2-0.24 mg kg-1 and vecuronium 0.05-0.06 mg kg-1. There was no significant difference in Tmax when equipotent doses of atracurium and vecuronium were compared.