The severe bronchospasm associated with rapacuronium, the cause is

Rapacuronium has effect on M2 and M3 muscarinic receptors in the bronchus. Activation of the postsynaptic M3 receptor by acetylcholine produces bronchoconstriction and the effect is terminated by presynooptic M2 receptors. Repacuronium blocks M2 receptor and has little effect on M3 so bronchoconstriction.