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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a vital role in numerous biochemical reactions. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of pre-eclampsia and eclampsia.
* Management of torsades de pointes.
* Treatment of severe asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4-6 g IV infused over 10-15 minutes, followed by 1-2 g/hour by continuous infusion. Dose may be repeated if symptoms persist.
* Less severe deficiency: 1-2 g IV or IM every 4-6 hours for 3-4 doses.
* **Pre-eclampsia/Eclampsia:** Loading dose: 4-6 g IV infused over 5-20 minutes. Maintenance infusion: 1-2 g/hour. If IM administration is used, 5 g in each buttock initially, followed by 5 g every 4 hours. Dosing can vary significantly based on institutional protocols and patient response.
* **Torsades de Pointes:** 1-2 g IV as a bolus, followed by 0.5-1 g/hour infusion.
* **Asthma Exacerbation:** 2 g IV infusion over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and often guided by serum magnesium levels and clinical status. A common regimen is 25-50 mg/kg/dose IV every 4-6 hours. Maximum single dose typically not to exceed 2 g.
* **Eclampsia:** Similar to adults, but specific pediatric protocols should be consulted.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, administer with caution and consider dose reduction. Monitor serum magnesium levels closely. Avoid in severe renal failure.
## Contraindications
* Heart block.
* Myocardial infarction.
* Hypermagnesemia.
* Hypocalcemia (use with caution as magnesium can worsen hypocalcemia).
* Intestinal obstruction.
* Hyperkalemia.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged respiratory depression.
* **Calcium Channel Blockers:** May increase the risk of hypotension and bradycardia.
* **Tetracyclines, Bisphosphonates:** Magnesium can reduce the absorption of orally administered tetracyclines and bisphosphonates. Separate administration by at least 2-4 hours.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially during continuous infusions or in patients with renal impairment. Target levels vary by indication.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Neurological Status:** Deep tendon reflexes, level of consciousness.
* **Urine Output:** To assess renal function.
* **Electrocardiogram (ECG):** Monitor for arrhythmias, especially with high doses or rapid infusion.
## Clinical Pearls
* Rapid IV infusion can cause hypotension, flushing, and electrocardiographic changes.
* IM injection can be painful; consider mixing with 1% procaine or lidocaine if available and appropriate.
* Always check serum calcium levels when treating hypomagnesemia, as they often coexist and magnesium replacement can unmask or worsen hypocalcemia.
* Eclamptic seizures may recur after initial magnesium therapy; continuous monitoring and potential redosing are crucial.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive guidance.
