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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte supplement and anticonvulsant. It is available in parenteral (IV/IM) and oral forms.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Treatment of status epilepticus refractory to other agents.
* Management of torsades de pointes.
* Adjunct in severe asthma exacerbations.
## Adult Dosing
**Hypomagnesemia:**
* **Severe deficiency (<1.0 mEq/L):** 4-6 grams (32-48 mEq) IV infused over 15-60 minutes, followed by a continuous infusion of 1-2 grams/hour (8-16 mEq/hr) until serum magnesium is >2.0 mEq/L.
* **Mild deficiency (1.0-1.5 mEq/L):** 2-4 grams (16-32 mEq) IV infused over 15-60 minutes.
* **IM administration:** 1 gram (8 mEq) IM every 6 hours for 4 doses.
* **Oral administration:** Dosing varies widely depending on the product and indication (e.g., laxative effect).
**Preeclampsia/Eclampsia:**
* **Loading Dose:** 4-6 grams (32-48 mEq) IV infused over 5-10 minutes.
* **Maintenance Dose:** 1-2 grams/hour (8-16 mEq/hr) IV infusion. Dosing may vary based on local protocol or patient response.
**Torsades de Pointes:**
* 1-2 grams (8-16 mEq) IV bolus, followed by infusion of 1 gram/hour (8 mEq/hr).
**Status Epilepticus:**
* 1-2 grams (8-16 mEq) IV infused over 15-30 minutes. May be repeated.
## Pediatric Dosing
Dosing in pediatrics is often weight-based and may vary by indication and institution.
**Hypomagnesemia:**
* **IV:** 25-50 mg/kg/dose (2-4 mEq/kg/dose) infused over 10-30 minutes. Maximum dose typically 2 grams. Maintenance infusion may be required.
**Eclampsia (off-label):**
* **Loading Dose:** 40 mg/kg (approximately 4 mEq/kg) IV infused over 10 minutes. Maximum 2 grams.
* **Maintenance Dose:** 10-20 mg/kg/hour (approximately 1-2 mEq/kg/hr) IV infusion. Maximum 6 grams/day.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely in patients with impaired renal function. For severe renal impairment, avoid parenteral administration if possible.
## Contraindications
* Hypermagnesemia.
* Heart block (unless a temporary pacemaker is in place).
* Myocardial infarction.
* A-V conduction abnormalities.
* Thecal sac rupture (with intrathecal administration).
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes, hypothermia.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (especially in renal impairment), hyperthermia, ileus.
## Key Drug Interactions
* **Calcium Salts:** Can antagonize the effects of magnesium.
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory paralysis.
* **Nifedipine:** Concurrent use may increase risk of hypotension and neuromuscular blockade.
* **Tetracyclines, Bisphosphonates, Fluoroquinolones:** Oral magnesium can decrease absorption of these drugs; separate administration by at least 2-3 hours.
## Monitoring
* Serum magnesium levels (initially every 4-6 hours, then less frequently as stable).
* Renal function (BUN, creatinine).
* Deep tendon reflexes.
* Respiratory rate and effort.
* Blood pressure.
* Urine output.
* ECG if concerns for cardiac effects or high doses.
## Clinical Pearls
* Always dilute IV magnesium sulfate before administration. Rapid infusion can cause hypotension and cardiac depression.
* Monitor reflexes; loss of reflexes is an early sign of magnesium toxicity.
* Ensure adequate urine output before and during therapy, especially in patients with renal impairment.
* When treating hypomagnesemia, consider concurrent correction of potassium and calcium if indicated.
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***Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Always consult the most current prescribing information and follow institutional protocols for definitive patient care decisions.*
