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# Magnesium Sulphate
## Overview
Magnesium sulfate is an essential mineral that plays a crucial role in various physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity.
## Primary Indications
* **Hypomagnesemia:** Treatment of low magnesium levels.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia (Torsades de Pointes), especially when associated with a prolonged QT interval.
* **Bronchospasm:** Adjunctive therapy in severe asthma or COPD exacerbations unresponsive to standard bronchodilators.
* **Constipation:** (Oral form only) As a laxative.
## Adult Dosing
* **Hypomagnesemia:**
* **Intravenous (IV):** 2-6 grams diluted in 100 mL of D5W or NS, infused over 5-60 minutes. May repeat doses every 4 hours as needed. Alternatively, a continuous infusion of 1-2 grams per hour may be used. Specific target serum magnesium levels should guide therapy.
* **Intramuscular (IM):** 1-4 grams every 4-6 hours.
* **Eclampsia/Preeclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5-20 minutes.
* **Maintenance Dose:** 1-2 grams per hour IV infusion. (Dosing may vary based on local protocols and patient response).
* **Torsades de Pointes:**
* **IV:** 1-2 grams diluted in 10 mL of D5W, infused rapidly (e.g., over 5-10 minutes). May repeat boluses, followed by a continuous infusion of 0.5-1 gram per hour.
* **Bronchospasm:**
* **IV:** 1-2 grams diluted in 100 mL of D5W or NS, infused over 15-30 minutes.
* **Constipation (Oral):**
* **Oral Solution:** 10-30 mL (equivalent to 1-3 grams magnesium citrate) as a single dose.
* **Tablets:** 2-4 tablets (each typically 500 mg magnesium oxide) with water.
## Pediatric Dosing
* **Hypomagnesemia:**
* **IV:** 25-50 mg/kg per dose (maximum 2 grams per dose), diluted and infused over 10-20 minutes. May repeat every 4-6 hours as needed. For continuous infusion, 10-20 mg/kg/hr.
* **Eclampsia/Preeclampsia:**
* Dosing is often based on adult protocols and adjusted for weight. Consult specific pediatric guidelines or local protocols.
* **Torsades de Pointes:**
* **IV:** 25-50 mg/kg per dose (maximum 2 grams per dose), infused over 10-20 minutes.
* **Bronchospasm:**
* **IV:** 25-50 mg/kg (maximum 2 grams), infused over 15-30 minutes.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Reduce dose and monitor serum magnesium levels closely. Avoid if severe renal failure and hypermagnesemia is present.
## Contraindications
* Hypermagnesemia
* Heart block (greater than first-degree) in the absence of a pacemaker
* Myocardial infarction (use with caution)
* Intestinal obstruction or perforation (oral form)
* Anuria (oral form)
* Hypersensitivity to magnesium sulfate
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, nausea, vomiting, somnolence, decreased reflexes.
* **Serious:** Respiratory depression, cardiac arrest, muscle weakness, hypermagnesemia (symptoms include hyporeflexia, decreased respiratory rate, confusion, coma, cardiac arrhythmias).
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., rocuronium, succinylcholine):** Magnesium sulfate can potentiate neuromuscular blockade, leading to prolonged paralysis and respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects.
* **Digitalis Glycosides:** Hypermagnesemia can increase the risk of digitalis toxicity.
* **Tetracyclines and Bisphosphonates:** Oral magnesium sulfate can decrease the absorption of these drugs; administer at least 2 hours apart.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV administration and in patients with renal impairment. Therapeutic targets vary by indication.
* **Renal Function:** Monitor BUN and creatinine.
* **Deep Tendon Reflexes:** Monitor for hyporeflexia, an early sign of hypermagnesemia.
* **Respiratory Rate and Effort:** Monitor for signs of respiratory depression.
* **Blood Pressure and Heart Rate:** Monitor for hypotension and cardiac arrhythmias.
* **Urine Output:** Monitor for adequate renal function.
## Clinical Pearls
* Magnesium sulfate administration can cause flushing and a feeling of warmth, which are typically transient.
* Always ensure adequate hydration and renal function before administering magnesium sulfate, especially intravenously.
* In eclampsia, continuous IV infusion is preferred for seizure prophylaxis.
* The IM route is painful and requires deep injection into a large muscle.
* For IV administration, dilute magnesium sulfate to prevent local irritation and reduce the risk of phlebitis.
* Oral magnesium sulfate is generally considered safe for short-term use as a laxative but can cause diarrhea and electrolyte disturbances with chronic use.
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***Disclaimer:** This information is intended for healthcare professionals. Always verify current prescribing information, institutional protocols, and patient-specific factors before making clinical decisions. The provided dosing is a general guideline and may require individual adjustment.*
