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# Magnesium Sulphate
## Overview
Magnesium sulfate is an essential mineral involved in numerous physiological processes, including neuromuscular transmission, cardiac function, and enzyme activity.
## Primary Indications
* **Hypomagnesemia:** Treatment of documented magnesium deficiency.
* **Preeclampsia/Eclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia (Torsades de Pointes), particularly when associated with a prolonged QT interval.
* **Status Asthmaticus:** Adjunctive therapy in severe, acute asthma refractory to standard treatment.
## Adult Dosing
Dosing varies significantly based on indication and route of administration.
* **Hypomagnesemia:**
* **Severe deficiency:** Typically 4-5 grams (32-40 mEq) intravenously over 5-60 minutes, followed by 1-2 grams (8-16 mEq) per hour infusion as needed to maintain serum magnesium levels.
* **Less severe deficiency:** 1-2 grams (8-16 mEq) intravenously or intramuscularly every 4-6 hours for 3-4 doses.
* **Preeclampsia/Eclampsia:**
* **Loading dose:** 4-6 grams (32-48 mEq) intravenously, usually infused over 5-20 minutes.
* **Maintenance infusion:** 1-2 grams (8-16 mEq) per hour. Dosing may be adjusted based on seizure control and magnesium levels. Local protocols are essential.
* **Torsades de Pointes:**
* **Acute treatment:** 1-2 grams (8-16 mEq) diluted in 10-20 mL of D5W, infused intravenously over 5-10 minutes.
* **If Torsades persists or recurs:** Repeat dose as above, followed by a continuous infusion of 0.5-1 gram (4-8 mEq) per hour.
* **Status Asthmaticus:**
* **Adjunctive therapy:** 1-2 grams (8-16 mEq) diluted in 50-100 mL of normal saline or D5W, infused intravenously over 15-20 minutes.
## Pediatric Dosing
Dosing in pediatrics is weight-based and indication-dependent. Local protocols are crucial.
* **Hypomagnesemia:** Doses of 25-50 mg/kg (0.2-0.4 mEq/kg) per dose intravenously or intramuscularly every 4-6 hours for 3-4 doses. Higher doses or continuous infusions may be used for severe deficiency.
* **Eclampsia:** Similar to adults, with loading doses of 40-50 mg/kg (0.32-0.4 mEq/kg) and maintenance infusions of 10-20 mg/kg/hr (0.08-0.16 mEq/kg/hr).
* **Torsades de Pointes:** 25-50 mg/kg (0.2-0.4 mEq/kg) intravenously, maximum 2 grams. Continuous infusion may follow.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with severe renal impairment, magnesium administration should be approached with caution, and serum magnesium levels should be closely monitored to avoid accumulation and toxicity. Dosing may need to be reduced or spaced further apart.
## Contraindications
* **Hypermagnesemia:** Patients with existing elevated serum magnesium levels.
* **Myocardial damage:** Generally avoided in patients with significant myocardial damage.
* **Heart block:** Use with caution in patients with heart block, particularly those with a damaged cardiac conduction system.
* **Severe renal failure:** Use with extreme caution or avoid.
## Adverse Effects
Common adverse effects include:
* Flushing
* Warm sensation
* Hypotension
* Drowsiness
* Nausea
* Vomiting
* Diarrhea (especially with oral administration)
Serious adverse effects include:
* Respiratory depression
* Loss of deep tendon reflexes
* Cardiac arrhythmias
* Cardiac arrest
* Hypermagnesemia (symptoms include decreased deep tendon reflexes, hypotension, somnolence, respiratory depression, arrhythmias, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., rocuronium, vecuronium):** Magnesium can potentiate neuromuscular blockade, leading to prolonged neuromuscular weakness or paralysis.
* **Calcium Channel Blockers:** Additive hypotensive effects and potential for enhanced cardiac depression.
* **Nifedipine:** Cases of profound muscle weakness have been reported when magnesium sulfate and nifedipine were co-administered.
* **Tetracycline antibiotics, bisphosphonates, iron supplements:** Oral magnesium can decrease the absorption of these medications; separate administration by at least 2-3 hours.
## Monitoring
* **Serum Magnesium Levels:** Crucial, especially with prolonged infusions or in patients with renal impairment. Therapeutic range typically 2.0-3.5 mEq/L (1.0-1.7 mmol/L) for seizure prophylaxis in preeclampsia; higher levels may be targeted for Torsades de Pointes.
* **Renal Function:** Monitor creatinine and BUN.
* **Deep Tendon Reflexes:** Assess for signs of toxicity.
* **Respiratory Rate:** Monitor for depression.
* **Blood Pressure:** Monitor for hypotension.
* **Urine Output:** Adequate urine output is essential for magnesium excretion.
## Clinical Pearls
* Magnesium sulfate should be administered slowly and with caution, particularly intravenously, to avoid hypotension and respiratory depression.
* Always have calcium gluconate (or calcium chloride) readily available as an antidote for severe magnesium toxicity.
* In hypomagnesemia, correction of potassium and calcium levels may be necessary as these electrolytes are often depleted concurrently.
* Intramuscular administration can be painful; consider co-administration with lidocaine if intramuscular route is necessary and local protocol allows.
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*This information is for educational purposes only and does not substitute for professional medical advice. Always consult with a qualified healthcare provider for any health concerns or before making any decisions related to your health or treatment. Verify current prescribing information with the latest official drug product labeling and relevant clinical guidelines.*
