Neuromuscular interactions between suxamethonium and magnesium sulphate in the cat

Abstract

In order to study the neuromuscular interactions between suxamethonium and magnesium sulphate (MgSO4), we have determined the dose-response relationship of suxamethonium and the neuromuscular actions of 1.25 x ED50 dose of suxamethonium, both before and after pretreatment with MgSO4. We have also compared the effect of 1.25 x ED50 dose of suxamethonium in the absence and in the presence of 50% neuromuscular block, established previously by infusion of MgSO4. Twenty-one cats were anaesthetized with urethane. Train-of-four stimulation was applied every 12 s to the sciatic nerve and the force of contraction of the tibialis anterior muscle was measured. The potency of suxamethonium decreased in each instance with pretreatment with MgSO4. The ED50 of suxamethonium increased significantly from mean 21.0 (SEM 1.9) micrograms kg-1 before MgSO4 to 25.6 (2.3) micrograms kg-1 after MgSO4 60 mg kg-1 and to 26.6 (2.2) micrograms kg-1 after MgSO4 90 mg kg-1 (P < 0.05). Twitch depression produced by 1.25 x ED50 dose of suxamethonium decreased significantly with MgSO4 pretreatment, from 76.7 (2.6)% before MgSO4 to 61.7 (6.4)% after MgSO4 60 mg kg-1 and 48.7 (7.5)% after MgSO4 90 mg kg-1 (P < 0.05). With stable 50% neuromuscular block, established previously by infusion of MgSO4, the 1.25 x ED50 dose of suxamethonium produced more twitch augmentation (133 (6.3)% vs 108.3 (1.3)%; P < 0.05) and less twitch depression (31.6 (9.6)% vs 74.1 (0.6)%, P < 0.05) than in the absence of MgSO4. The results of all three methods demonstrated that the pharmacological interaction between suxamethonium and magnesium was antagonistic.

Magnesium: physiology and pharmacology

“…88 However, the most recent study suggests that magnesium may antagonize the block produced by succinylcholine. 172 This study found a 20% reduction in twitch suppression produced by succinylcholine 1.25ϫED 50 after pretreatment with magnesium sulphate 90 mg kg -1 , and a 20% increase in the ED 50 of succinylcholine after the same dose of magnesium sulphate. An increase in twitch height was also found when succinylcholine 1.25ϫED 50 was given in the presence of 50% neuromuscular block produced by magnesium sulphate.…”

Physiologische Effekte, Pharmakologie und Indikationen zur Gabe von Magnesium

“…Nach Gabe von Magnesium in einer für die Behandlung einer EPH-Gestose adäquaten Dosierung zeigte sich die ED 50 von Vecuronium um 25% reduziert, die Onset-Zeit fast halbiert und die Erholungszeit verdoppelt [7]. Eine partielle Inhibition der durch Succinylcholin verursachten neuromuskulären Blockade durch Magnesium wurde beschrieben [36]. Eine partielle Inhibition der durch Succinylcholin verursachten neuromuskulären Blockade durch Magnesium wurde beschrieben [36].…”

Concurrent medication and the neuromuscular junction

“…There was no significant increase in serum K + concentration after pretreatment with magnesium sulphate before suxamethonium administration [46]. In one study, in the cat, antagonism between suxaÍmethonium and Mg 2+ was demonstrated [47]. A bolus of magnesium sulphate may reduce the hypertensive response to laryngoscopy and intubation [48].…”