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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a vital role in numerous biochemical functions. It is available for intravenous and intramuscular administration.
## Primary Indications
* Treatment of hypomagnesemia
* Prevention and treatment of eclampsia in pregnant patients
* Management of torsades de pointes
## Adult Dosing
* **Hypomagnesemia:**
* Mild: 4 g IV infused over 4 hours.
* Severe: 4-8 g IV initially, followed by 2-4 g IV every 4-12 hours as needed. Dosing may be repeated for up to 4 doses.
* IM: 1 g every 6 hours for 4 doses.
* **Eclampsia:**
* Loading dose: 4-6 g IV infused over 5-10 minutes.
* Maintenance infusion: 1-2 g/hour. Alternatively, 5 g IM in each buttock (total 10 g) if IV access is unavailable, followed by 5 g IM every 4 hours.
* **Torsades de Pointes:**
* 2-4 g IV bolus, followed by an infusion of 1-2 g/hour.
## Pediatric Dosing
* **Hypomagnesemia:**
* Dosing is highly variable and based on calculated magnesium deficit. A common starting point is 25-50 mg/kg/dose (elemental magnesium) IV infused over 1-2 hours. Maximum dose typically 2 g.
* **Eclampsia:**
* Refer to obstetric guidelines; dosing is similar to adults but may require careful monitoring due to immature renal function.
## Dose Adjustments
* **Renal Impairment:** Use with extreme caution. Reduce dose and monitor serum magnesium levels closely. Accumulation can lead to toxicity. Dosing adjustments are not well-established and depend on the degree of renal impairment.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (relative contraindication, especially in the acute phase)
* Hypotension (relative contraindication)
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, nausea, vomiting, lethargy, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (muscle weakness, absent reflexes, ECG changes, bradycardia, respiratory arrest, cardiac arrest), hyperthermia, diaphoresis.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade. Monitor for prolonged muscle weakness and respiratory depression.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and Quinolones:** Magnesium can reduce the absorption of these antibiotics. Administer at least 2-4 hours apart.
* **Digoxin:** High doses of IV magnesium sulphate may increase digoxin toxicity.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with repeated dosing or in renal impairment. Target levels vary by indication (e.g., 4-7 mg/dL for eclampsia).
* **Renal Function (BUN, Creatinine):** Assess baseline and monitor for changes.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for presence and symmetry. Diminished reflexes can indicate hypermagnesemia.
* **Urine Output:** Monitor for adequate output.
## Clinical Pearls
* Magnesium sulphate is often administered as a 50% solution (500 mg/mL). Ensure correct calculation of elemental magnesium.
* Rapid IV infusion can cause flushing, hypotension, and cardiac arrhythmias. Infuse as recommended.
* IM injections can be painful; consider dilution with lidocaine (though this is not universally practiced and may be facility-specific).
* Magnesium administration can antagonize calcium effects; calcium gluconate may be considered as an antidote in cases of severe magnesium toxicity.
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*This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always verify current prescribing information, institutional protocols, and patient-specific factors before making clinical decisions.*
