PRIMING AND THE ONSET OF NEUROMUSCULAR BLOCKADE WITH ALCURONIUM

"Priming", applied to non-depolarizing neuro-muscular blocking agents, is the practice of giving a small (priming) portion of a dose some minutes before the balance, and achieving thereby a more rapid onset of action, or a more intense or long-lasting blockade, than if the same total dose had been given undivided (Foldes, 1984). One obvious explanation, for the more rapid onset at least, is that the priming dose occupies the 70-80 % of "spare receptors " which must be occupied before any effects of non-depolarizing blockers become apparent (Paton and Waud, 1967). The term "priming " was coined by Foldes (1984) in a brief report on short intubation times with a range of non-depolarizing blockers, when the priming dose was given 6-8 min before the induction of anaesthesia with the balance given at induction. This practice should possibly be qualified as "pre-induction priming". Foldes' report was preceded by that of Gergis and colleagues (1983) on "pre-induction priming" with atracurium, and by ours (Hutton et al., 1983) on "post-induction priming " with alcuronium— that is, the priming dose-was given shortly after induction and the balance administered 4 min later. More recently, Schwartz and co-workers (1985) and Mehta and associates (1985) have published studies which include both pre- and post-induc-tion priming. In an editorial comment, Mille