THE EFFECT OF RESIDUAL RECEPTOR OCCUPANCY ON SENSITIVITY TO REPEATED VECURONIUM

Cumulative dose‐response curves were obtained for vecuronium in 10 patients anaesthetised with thiopentone, enflurane and nitrous oxide using adductor pollicis mechanomyography. Five patients received vecuronium systemically, which was repeated at 100% twitch recovery to obtain initial and repeat curves. Another five patients received 0.3 mg vecuronium into an isolated forearm and at 100% recovery of this arm received vecuronium systemically to obtain simultaneous dose‐response curves in both the previously isolated and nonisolated arms. There was no significant difference between the calculated ED50 obtained after initial systemic administration [16.2 (1.7) μg.kg−1], after recovery in the previously isolated arm [14.8 (2.0) μg.kg−1] and simultaneously in the nonisolated arm [16.1 (2.9) μg.kg−1]. The ED50 obtained after repeated systemic administration was significantly reduced [8.2 (2.9) μ.kg−1]. These results suggest that the reduction in ED50 at 100% twitch recovery from systemic vecuronium is not due to residual drug at the biophase/receptor but to drug persisting in the plasma. Copyright © 1993, Wiley Blackwell. All rights reserved