Interaction between nondepolarizing muscle relaxants.

Abstract

A. W. Harrop-Griffiths, M.A., M.B., B.S., F.R.C.A., Consultant Anaesthetist; J. R. Hood, M.B., B.S., F.R.C.A., Senior Registrar in Anaesthesia, Department of Anaesthesia, St. Mary's Hospital, Praed Street, London W2 1NY, United Kingdom.To the Editor:-In a recent article, Erkola et al. [1]demonstrated that a shorter-acting muscle relaxant (mivacurium), if administered after a longer-acting muscle relaxant (pancuronium), takes on the characteristics of the first drug. Unfortunately, the authors did not take the opportunity to study a cross-over group (i.e., a group to whom pancuronium was given after mivacurium). Had they done so, it is highly likely that they would have observed the phenomenon reported by Feldman et al. in 1993. [2]In this study in the isolated forearm, the authors observed that the administration of pancuronium after 50% recovery from a vecuronium-induced block led to a reduction in pancuronium recovery index. Therefore, the recovery from the effects of one nondepolarizing muscle relaxant given after partial recovery from another more resembles the recovery from the muscle relaxant given first.Had Erkola et al. been aware of this previously published work, it is unlikely they would have suggested that pancuronium's capacity to inhibit pseudocholinesterase may be responsible for the prolongation of the effect of mivacurium or that the effect they observed was due to the long beta half-life of pancuronium. A more tempting hypothesis is put forward by Feldman et al. [2](i.e., that the second drug displaces some of the first drug that remains in the biophase onto the acetylcholine receptors and that, therefore, much of the block elicited by the second drug is actually effected by the proportion of the first drug, which remains in the biophase). The recovery, therefore, resembles that of the first drug.A. W. Harrop-Griffiths, M.A., M.B., B.S., F.R.C.A., Consultant Anaesthetist; J. R. Hood, M.B., B.S., F.R.C.A., Senior Registrar in Anaesthesia, Department of Anaesthesia, St. Mary's Hospital, Praed Street, London W2 1NY, United Kingdom.(Accepted for publication October 10, 1996.)