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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral used to treat and prevent hypomagnesemia, as well as in specific obstetric and cardiac conditions.
## Primary Indications
* Hypomagnesemia
* Preeclampsia and eclampsia
* Torsades de pointes
* Status asthmaticus (adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4-6 grams IV initially, followed by 1-2 grams per hour via continuous infusion.
* Less severe deficiency: 1-2 grams IV or IM every 4-6 hours as needed.
* Maintenance: 4-6 grams IM or IV divided into 4 doses over 24 hours.
* **Preeclampsia/Eclampsia:**
* Loading dose: 4-6 grams IV infused over 5-10 minutes.
* Maintenance infusion: 1-2 grams per hour IV. Adjustments based on clinical response and toxicity.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. May repeat as needed.
* **Status Asthmaticus:** 2 grams IV diluted in 50-100 mL NS or LR over 15-30 minutes.
Dosing for specific indications may vary based on institutional protocols.
## Pediatric Dosing
* **Hypomagnesemia:**
* 10-20 mg/kg (elemental magnesium) IV infused over 1-2 hours. Maximum dose typically 2 grams.
* Can be repeated every 4-6 hours as needed.
* Further maintenance dosing is highly individualized.
* **Eclampsia:** Dosing typically follows adult guidelines, but with caution and close monitoring.
Pediactric dosing can be complex and requires careful calculation of elemental magnesium.
## Dose Adjustments
* **Renal Impairment:** Magnesium sulfate is renally excreted. Dose reduction and careful monitoring of magnesium levels and renal function are crucial in patients with impaired renal function. Avoid in severe renal impairment if possible.
## Contraindications
* Hypermagnesemia
* Myocardial conduction defects
* Heart block
* AV block
* Severe renal impairment (use with extreme caution)
* Hypersensitivity to magnesium sulfate
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, sweating, nausea, vomiting, decreased reflexes, somnolence.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (muscle weakness, absent deep tendon reflexes, ECG changes, difficulty breathing, cardiac arrhythmias).
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade, increasing the risk of prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of hypermagnesemia.
* **Digitalis:** May worsen cardiac conduction abnormalities.
* **Tetracyclines and Quinolones:** Magnesium sulfate can decrease the absorption of these antibiotics; administer at least 2-4 hours apart.
## Monitoring
* Serum magnesium levels (especially with prolonged infusion or renal impairment). Therapeutic range for hypomagnesemia is typically 1.7-2.2 mmol/L (4.0-5.3 mg/dL), but may be higher for eclampsia.
* Deep tendon reflexes (loss of reflexes is an early sign of toxicity).
* Respiratory rate and depth.
* Blood pressure.
* Urine output.
* Renal function (BUN, creatinine).
* ECG for signs of hypermagnesemia.
## Clinical Pearls
* Magnesium sulfate administration can cause flushing and a feeling of warmth, which is typically transient.
* Always have calcium gluconate readily available as an antidote for magnesium toxicity.
* When treating hypomagnesemia, consider the cause (e.g., alcoholism, malabsorption, diuretic use) and address it if possible.
* In preeclampsia/eclampsia, continued monitoring for seizures is essential even after magnesium administration.
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*Please verify current prescribing information and institutional protocols before administration.*
