Interaction of muscle relaxants [vecuronium and pancuronium] and local anaesthetics [bupivacaine and xylocaine] at the neuromuscular junction: a quantitative experimental study

Local anesthetics produce neuromuscular block, ganglionic block, and anticholinergic activity. This action is a dose dependent through interference with prejunction release of acetylcholine, stabilize post-junctional membranes, and directly depress muscle fibers. This study was done experimentally on isolated rat phrenic-nerve diaphragm preparation to test the interaction between vecuronium and pancuronium with bupivacaine and xylocaine. Bupivacaine caused reduction of contraction height produced by vecuronium from 56 +/- 2.9% to 74.5 +/- 5.35% and that produced by pancuronium from 49.4 +/- 3.06% to 66.4 +/- 4.48%. Xylocaine reduced the contraction height induced by vecuronium to 90.65 +/- 5.95% and that induced by pancuronium to 90.65 +/- 4.15%. This effect was not antagonized by calcium gluconate. Reversal of muscle relaxation by neostigmine was not affected by the local anesthetics