Potency determination for vecuronium (ORG NC45): comparison of cumulative and single-dose techniques

To compare two methods of estimating the potency of neuromuscular relaxants of medium duration, the authors determined the potency of vecuronium (ORG NC45) using cumulative dose-response (CDR) techniques, and compared these data with published values from our group obtained using the single bolus technique. During 60% N2O-halothane anesthesia, patients received 10 micrograms/kg vecuronium; additional incremental doses of vecuronium, 5 micrograms/kg, were given when no change occurred in the height of three successive twitches. Using these dose-response data, the authors determined least-squares regression lines and ED20, ED50, and ED80. These results were compared to values obtained by the single bolus technique under comparable conditions. The CDR and single bolus technique yielded ED50 values of 19.9 and 15.0 micrograms/kg, respectively. All potency estimates by CDR were larger than those obtained by the single bolus dose technique. It was concluded that, for vecuronium, a medium duration neuromuscular relaxant, CDR yields potency estimates which are larger than those obtained by the traditional single bolus dose technique. Because the single bolus dose technique is the accepted method for construction of dose-response curves, the authors recommended that CDR not be used for potency determination of muscle relaxants of medium and short duration such as vecuronium.