Magnesium sulphate intravenously reduces tachycardia side-effects of β₂-agonists

The review by Erumbala et al. [1] correctly proposing magnesium sulphate (MgSO₄) as the first intravenous bronchodilator missed vital points of its pharmacological actions. The i.v. drug reduces or eliminates tachycardia and palpitation side-effects of β₂-agonists [2–5]. As well as relaxing smooth muscle of the bronchi, vasculature, gut and uterus, MgSO₄ slows cardiac atrial conduction [6, 7], and was used in the past to revert supraventricular tachycardia and fast atrial fibrillation [8, 9]. There is no evidence to be found for the 20–30 min infusion rate for i.v. MgSO₄ of 40–75 mg.kg⁻¹, and this infusion time will not create a sufficiently high serum level to relax bronchial smooth muscle. In acute-severe and life-threatening asthma i.v. MgSO₄ followed by i.v. β₂-agonist is safe [10]; an infusion time of 5 min for MgSO₄ has evidence for the safety of this speed of injection in obstetric [11] and cardiac literature, albeit in adults.

Short abstract

Intravenous magnesium sulphate allows safer intravenous β₂-agonist delivery in acute-severe and life-threatening asthma attacks https://bit.ly/3veUpfC

To the Editor:

The review by Erumbala et al. [1] correctly proposing magnesium sulphate (MgSO₄) as the first intravenous bronchodilator missed vital points of its pharmacological actions. The i.v. drug reduces or eliminates tachycardia and palpitation side-effects of β₂-agonists [2–5]. As well as relaxing smooth muscle of the bronchi, vasculature, gut and uterus, MgSO₄ slows cardiac atrial conduction [6, 7], and was used in the past to revert supraventricular tachycardia and fast atrial fibrillation [8, 9]. There is no evidence to be found for the 20–30 min infusion rate for i.v. MgSO₄ of 40–75 mg.kg⁻¹, and this infusion time will not create a sufficiently high serum level to relax bronchial smooth muscle. In acute-severe and life-threatening asthma i.v. MgSO₄ followed by i.v. β₂-agonist is safe [10]; an infusion time of 5 min for MgSO₄ has evidence for the safety of this speed of injection in obstetric [11] and cardiac literature, albeit in adults.