Priming and the onset of neuromuscular blockade with alcuronium.

"Priming" with alcuronium has been studied in 72 female patients. Blockade of single twitch responses of the adductor pollicis by alcuronium 0.15, 0.2 or 0.3 mg kg-1 could be accelerated by priming with a suitable priming portion of the total dose. Giving alcuronium 0.04 mg kg-1 30 s after the induction of anaesthesia, followed by the balance 4 min later, resulted in more rapid neuromuscular blockade than giving the total dose at 4.5 min after induction. There was some suggestion of an increase in maximal twitch depression, but this could not be demonstrated confidently. The effect of increasing the priming portion was tested for the 0.3 mg kg-1 total dose, but any priming effect was attenuated. The mechanism of priming is not obvious. Occupation of "spare receptors" does not explain all of the features of priming.