Background
Neuromuscular blocking agents are an integral component of general anesthesia. In addition to their intended pharmacologic target on skeletal muscle nicotinic receptors, undesirable airway effects (i.e. bronchoconstriction) can result from neuromuscular blocking agents affinity for airway muscarinic receptors. We questioned whether two new members of a bisquaternary non-depolarizing muscle relaxant family, gantacurium and CW002, demonstrated detrimental effects of airway muscarinic receptors using an in vivo model in guinea pig airways.
Methods
Urethane anesthetized male guinea pigs were ventilated through a tracheostomy with continuous digital recordings of pulmonary inflation pressure and heart rate. The ED95 for muscle paralysis for gantacurium, CW002, cisatracurium and rapacuronium were defined in the guinea pig. Transient and reproducible changes in pulmonary inflation pressure and heart rate were recorded following vagal nerve stimulation or the intravenous injection of acetylcholine before and after pretreatment with cumulatively increasing concentrations of gantacurium, CW002, cisatracurium or a single concentration of rapacuronium.
Results
Gantacurium, CW002, cisatracurium and rapacuronium exhibited ED95 for muscle paralysis of 0.064 ± 0.0006, 0.012 ± 0.006, 0.10 ± 0.003, and 0.31 ± 0.05 mg/kg, respectively. Gantacurium, CW002 and cisatracurium were without effects on baseline pulmonary inflation pressures and were devoid of significant interactions with M2 and M3 muscarinic receptors in vivo.
Conclusion
These findings suggest that gantacurium and CW002 are devoid of significant effects at airway muscarinic receptors particularly M3 receptors on bronchial smooth musculature at doses several fold higher than those required for functional muscle paralysis.