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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral involved in numerous biochemical processes. It can be administered intravenously or intramuscularly for various indications.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and pre-eclampsia.
* Treatment of torsades de pointes.
* Management of bronchospasm in asthma (adjunctive therapy).
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4 to 6 g IV initially, followed by 1 to 2 g/hour by continuous infusion for up to 24 hours.
* Milder deficiency: 1 to 2 g IV or IM every 6 to 12 hours for 4 doses.
* **Eclampsia/Pre-eclampsia:**
* Loading dose: 4 to 6 g IV over 5 to 20 minutes.
* Maintenance dose: 1 to 2 g/hour by continuous infusion. Some protocols may use IM doses (e.g., 5 g IM into each buttock, followed by 5 g IM every 4 hours).
* **Torsades de Pointes:** 1 to 2 g IV in 5% dextrose in water over 5 to 60 minutes. Repeat doses may be given.
* **Asthma (adjunctive):** 2 g IV in 50 mL 0.9% NaCl over 15 to 20 minutes.
## Pediatric Dosing
Dosing is highly variable and often determined by protocol. General guidelines:
* **Hypomagnesemia:** 25 to 50 mg/kg/dose IV or IM every 4 to 6 hours for 3 to 4 doses. Maximum single dose typically 2 g.
* **Eclampsia/Pre-eclampsia:** Consult specific obstetrical protocols; pediatric dosing is not typically established for this indication.
* **Torsades de Pointes:** 25 to 50 mg/kg/dose IV over 10 to 20 minutes. Maximum single dose typically 2 g.
* **Asthma (adjunctive):** 25 to 50 mg/kg IV over 15 to 30 minutes. Maximum dose typically 2 g.
## Dose Adjustments
Reduce dose and monitor closely in patients with **renal impairment**. No dose adjustment is typically needed for hepatic impairment.
## Contraindications
* Heart block (unless a temporary pacemaker is in place).
* Myocardial infarction.
* Hypermagnesemia.
* Hyperkalemia (caution).
* Anuria or severe renal dysfunction (relative contraindication, use with extreme caution and dose adjustment).
## Adverse Effects
* **Common:** Flushing, sweating, nausea, vomiting, hypotension, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, somnolence, coma, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular blocking agents:** Potentiates neuromuscular blockade.
* **Calcium channel blockers:** Increased risk of hypotension and bradycardia.
* **Antibiotics (aminoglycosides, polymyxins):** Additive neuromuscular blockade.
* **Diuretics:** May increase magnesium excretion.
## Monitoring
* **Magnesium levels:** Monitor serum magnesium levels regularly, especially with prolonged infusions or renal impairment. Therapeutic range is typically 1.7 to 2.2 mmol/L (4 to 7 mg/dL), but may vary by indication.
* **Renal function:** Monitor serum creatinine and BUN.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Assess for presence and grade.
* **Urine output:** Monitor for adequate urine output.
## Clinical Pearls
* Magnesium sulfate is highly irritating; dilute IV infusions and administer slowly.
* IM injections are painful; consider adding lidocaine.
* When treating hypomagnesemia, correct potassium and calcium levels as well, as they often coexist.
* Monitor for signs of magnesium toxicity, which can be life-threatening.
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*Please verify current prescribing information and institutional protocols before use, as recommendations may vary.*
