An Experimental Study to Optimize Neuromuscular Blockade Protocols in Cynomolgus Macaques: Monitoring, Doses, and Antagonism.

Background: Neuromuscular blocking agents (NMBAs) are a crucial component of anesthesia and intensive care through the relaxation of skeletal muscles. They can lead to adverse reactions such as postoperative residual neuromuscular block. Only one agent is capable of an instant block reversal in deep block situations, but is restricted to aminosteroid agents. Among animal models, non-human primates are an essential model for a great diversity of human disease models. The main objective of this study was to establish a model for NMBA monitoring with current available drugs before testing new reversal agents.

Methods: Seven healthy male cynomolgus macaques were randomly assigned to this study. Experiments using macaques were approved by the local ethical committee (CEtEA #44). All animals were anesthetized according to institutional guidelines, with ketamine and medetomidine, allowing IV line placement and tracheal intubation. Anesthesia was maintained with isoflurane. Either rocuronium bromine (with or without sugammadex reversal) or atracurium besylate was evaluated. Monitoring was performed with two devices, TOF-Watch and ToFscan, measuring the T4/T1 and the T4/Tref ratios, respectively. Nonparametric Mann-Whitney statistical analyses were done when indicated.

Results: NMBA monitoring required adaptation compared to humans, such as stimulus intensity and electrode placement, to be efficient and valid in cynomolgus macaques. When administered, both NMBAs induced deep and persistent neuro-muscular block at equivalent doses to clinical doses in humans. The rocuronium-induced profound neuromuscular block could be reversed using the cyclodextrin sugammadex as a reversal agent. We report no adverse effects in these models by clinical observation, blood chemistry, or complete blood count.

Conclusion: These results support the use of non-human primate models for neuromuscular block monitoring. This represented the first step before the forthcoming testing of new NMBA-reversal agents.