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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a role in numerous biochemical processes, including neuromuscular transmission and muscle contraction. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Management of torsades de pointes.
* Bronchodilator in severe asthma exacerbations (adjunctive therapy).
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4 to 6 grams of magnesium sulfate IV over 1 to 4 hours, followed by a maintenance infusion of 1 to 2 grams per hour.
* Less severe deficiency: 1 to 4 grams of magnesium sulfate IV or IM every 4 to 6 hours as needed.
* **Preeclampsia/Eclampsia Prophylaxis:** 4 grams of magnesium sulfate IV diluted in 100 mL of IV fluid, infused at 1 to 2 grams per hour as a continuous infusion.
* **Preeclampsia/Eclampsia Treatment (Seizures):** Loading dose: 4 to 6 grams of magnesium sulfate IV over 5 to 20 minutes. Maintenance dose: 1 to 2 grams per hour as a continuous infusion. Alternative IM dosing: 5 grams IM in each buttock (total 10 grams) initially, followed by 5 grams IM every 4 hours.
* **Torsades de Pointes:** 1 to 2 grams of magnesium sulfate IV diluted in 100 mL of D5W, infused over 5 to 10 minutes. May repeat as needed, followed by a continuous infusion of 0.5 to 1 gram per hour.
* **Asthma (Adjunctive):** 2 grams of magnesium sulfate IV diluted in 50 mL of NS or D5W, infused over 15 to 20 minutes.
*Maximum infusion rate for hypomagnesemia treatment is typically 1 gram/minute to avoid hypotension and flushing.*
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly based on age, weight, and severity of deficiency. Typically ranges from 25 to 100 mg/kg/dose IV or IM every 4 to 6 hours. Maximum single dose generally does not exceed 2 grams. Specific protocols should be followed.
* **Preeclampsia/Eclampsia Prophylaxis/Treatment:** Dosing is complex and often based on weight-based protocols. Typical maintenance infusion is 0.5 to 1 gram/kg/hour, with a maximum of 20 grams per day. Loading doses are also weight-based.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, doses should be reduced, and serum magnesium levels closely monitored to prevent hypermagnesemia. Guidelines suggest a reduction in maintenance dose for moderate to severe renal impairment.
## Contraindications
* Hypermagnesemia.
* Heart block greater than first degree or myocardial damage.
* Shock.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia, hypocalcemia, muscle weakness, arrhythmias.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate the effects of neuromuscular blockers, leading to prolonged paralysis.
* **Calcium Salts:** Concurrent administration may antagonize the effects of magnesium. Administer IV calcium separately from magnesium infusions.
* **Tetracyclines and Bisphosphonates:** Magnesium can decrease the absorption of orally administered tetracyclines and bisphosphonates. Separate administration by at least 2 hours (preferably longer).
## Monitoring
* **Serum Magnesium Levels:** Monitor at baseline and periodically during therapy, especially with prolonged infusions or in patients with renal impairment. Therapeutic range for hypomagnesemia is typically 2.5 to 7.5 mg/dL (1.0 to 3.0 mmol/L).
* **Renal Function:** Monitor creatinine and BUN.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate, especially during IV infusion.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, which can indicate hypermagnesemia.
* **Urine Output:** Monitor for adequate renal function.
* **ECG:** May be indicated in cases of suspected arrhythmias or severe hypermagnesemia.
## Clinical Pearls
* When treating hypomagnesemia, consider concurrent electrolyte abnormalities such as hypokalemia and hypocalcemia, as magnesium can affect their levels.
* Rapid IV administration can cause hypotension and flushing. Infuse slowly and monitor vital signs closely.
* In patients receiving IV magnesium for preeclampsia, monitor for signs of magnesium toxicity, including loss of deep tendon reflexes, respiratory depression, and altered mental status.
* Ensure adequate hydration and urinary output, particularly in patients with renal impairment.
*Please verify the most current prescribing information and institutional protocols before administering magnesium sulfate.*
