From the Guidelines
Magnesium sulfate works by blocking calcium channels, leading to smooth muscle relaxation, and its normal administration route is intravenously (IV) for acute conditions. The mechanism of action of magnesium sulfate involves blocking calcium channels and NMDA receptors in the body, resulting in smooth muscle relaxation, decreased neuromuscular excitability, and vasodilation 1. This effect is beneficial in various clinical conditions, including asthma, where it can improve pulmonary function and reduce hospital admissions, particularly in patients with severe exacerbations 1.
Administration Routes and Considerations
The most common administration route for magnesium sulfate is intravenously (IV) for acute conditions, though intramuscular (IM) injection may be used in obstetric settings. For IV administration, magnesium sulfate is typically given as a loading dose followed by continuous infusion, with dosing varying by indication. For example, in severe asthma, a dose of 2g IV over 20 minutes may be considered 1.
Key Considerations for Administration
- Careful monitoring of respiratory rate, deep tendon reflexes, urine output, and serum magnesium levels is essential to prevent toxicity.
- Magnesium sulfate requires caution in patients with renal impairment as the kidneys primarily excrete it, and toxic levels can cause respiratory depression, cardiac abnormalities, and hypotension 1.
- The use of magnesium sulfate in pregnancy, particularly for severe pre-eclampsia and eclampsia, is well established, though it should be managed with close maternal and fetal surveillance 1.
From the FDA Drug Label
Magnesium sulfate injection should not be given unless hypomagnesemia has been confirmed and the serum concentration of magnesium is monitored. CNS depression and peripheral transmission defects produced by magnesium may be antagonized by calcium
Magnesium does have an effect on calcium, but the mechanism of action is more related to its role as a calcium channel blocker, which can lead to smooth muscle relaxation. The normal administration routes for magnesium sulfate are:
- Intravenous (IV): suitable for adults and children, with a concentration of 20% or less prior to administration.
- Intramuscular (IM): suitable for adults, but the solution should be diluted to a 20% or less concentration prior to injection in children 2.
From the Research
Mechanism of Action
- Magnesium sulfate is a calcium antagonist that inhibits bronchial smooth muscle contraction, promoting bronchodilation 3.
- It works by blocking calcium channels, which allows smooth muscle relaxation.
Administration Route
- The normal administration route for magnesium sulfate is intravenous (IV) infusion 3, 4, 5, 6, 7.
- IV infusion is commonly used in emergency situations, such as acute severe asthma, to rapidly relieve bronchospasm and prevent respiratory failure 4, 7.