Neuromuscular interactions between mivacurium and esmolol in rabbits

We compared the dose–response relationship and the neuromuscular blocking effects of mivacurium during infusions of esmolol in 40 anaesthetised rabbits. Train-of-four stimuli were applied every 10 s to the common peroneal nerve and the force of contraction of the tibialis anterior muscle was measured. Plasma cholinesterase activity decreased by 13% after esmolol infusion. The ED₉₅ of mivacurium increased significantly from 29 (4.8) μgkg⁻¹ with placebo to 61 (9.8) μgkg⁻¹ during esmolol 100 μgkg⁻¹.min⁻¹, 49 (8.2) μgkg⁻¹ during esmolol 300 μgkg⁻¹.min⁻¹ and 54 (7.3) μgkg⁻¹ during esmolol 500 μgkg⁻¹.min⁻¹, respectively (p < 0.001). The duration of neuromuscular block with mivacurium 0.16 mgkg⁻¹ was prolonged by 30% with esmolol due to diminished plasma cholinesterase activity (p < 0.05). Heart rate and mean arterial blood pressure decreased by 15% with esmolol (p < 0.05). The results of this study show that, in rabbits, esmolol decreased plasma cholinesterase activity, antagonised the neuromuscular blocking potency of mivacurium and prolonged its neuromuscular blocking effect.