RESUMO
Interaction between vecuronium bromide (VB) and pancuronium bromide (PB) with regard to a change in duration of action was investigated in 32 elective surgical patients divided into four groups. Initial and supplemental drugs were as follow; group I: VB-->VB, group II: PB-->VB, group III: VB-->PB, group IV: PB-->PB. The muscle response was quantified electromyographically. Anesthesia was induced with thiopental. VB or PB 0.08 mg.kg-1 (initial dose) was given to facilitate endotracheal intubation. Anesthesia was maintained with 66% nitrous oxide and 2% sevoflurane in oxygen. Supplemental dose (0.015 mg.kg-1) of the muscle relaxants was administered at 10% recovery of twitch height. Duration of action was defined as the interval between administration and 10% recovery. Duration of action of supplemental doses of VB was significantly longer in group II than in group I. That of PB was significantly shorter in group III than in group IV. Therefore, it should be noticed that duration of action of supplemental relaxant is largely modified by the initial one.