Comparison of cumulative and single bolus dose techniques for determining the potency of vecuronium

The potency of vecuronium was determined using single bolus dose administrations of 10-50 micrograms kg-1 in 28 patients anaesthetized with thiopentone, nitrous oxide, oxygen and fentanyl. The results were compared with those previously obtained using a cumulative dose technique in a comparable group of 10 patients. The 50% and 95% blocking doses (ED50 and ED95) of vecuronium were found to be 23.1 and 39.6 micrograms kg-1, respectively. These were significantly lower than the 30.5 and 56.7 micrograms kg-1 obtained previously using the cumulative dose technique. We recommend the use of single bolus dose method of determining potency for relatively shorter-acting drugs like vecuronium.