Magnesium%2520sulphate

# Magnesium Sulphate ## Overview Magnesium sulphate is an essential electrolyte supplement and smooth muscle relaxant. It is used intravenously or intramuscularly for acute conditions and orally for replacement. Dosing varies significantly by indication; local protocols should be followed. ## Primary Indications - Hypomagnesemia (severe, symptomatic) - Pre-eclampsia/eclampsia (seizure prophylaxis/treatment) - Acute severe asthma (as bronchodilator adjunct) - Torsades de pointes (polymorphic VT) - Constipation (oral, chronic use) ## Adult Dosing - **Hypomagnesemia** (severe): IV 4–8 mmol (1–2 g) over 15–30 min, may repeat. Max single dose 20 mmol (5 g). - **Pre-eclampsia/eclampsia**: IV 4–5 g (16–20 mmol) loading dose over 15–20 min, then 1–2 g/hour infusion for 24 h after delivery/last seizure. Max 30–40 g/24h per protocol. - **Acute severe asthma**: IV 1.2–2 g (4.8–8 mmol) over 20 min (single dose). - **Torsades de pointes**: IV 2 g (8 mmol) over 1–2 min; may repeat once. - **Constipation** (oral): 5–15 g (20–60 mmol) daily in divided doses. ## Pediatric Dosing - **Hypomagnesemia**: IV 0.1–0.2 mmol/kg (25–50 mg/kg) over 2–4 h; may repeat. Max 2 g (8 mmol) per dose. - **Acute severe asthma**: IV 40–50 mg/kg (0.16–0.2 mmol/kg) over 20 min. Max 2 g. - **Seizures (eclampsia-like)**: IV 20–40 mg/kg (0.08–0.16 mmol/kg) loading, then 10–20 mg/kg/h infusion. Use locally validated protocols. - **Torsades de pointes**: IV 25–50 mg/kg (0.1–0.2 mmol/kg) over 1–2 min. Max 2 g. ## Dose Adjustments - **Renal impairment** (CrCl <30 mL/min): Reduce dose by 50–75%; monitor Mg levels closely. Avoid continuous infusions in severe impairment. - **Elderly**: Use lower end of dosing range; assess renal function. ## Contraindications - Myasthenia gravis (may exacerbate weakness) - Severe renal failure (unless dialysis readily available) - Heart block (unless paced) - Hypocalcemia (may worsen) ## Adverse Effects - **Common**: Flushing, sweating, hypotension, nausea - **Serious**: Respiratory depression, bradycardia, cardiac arrest (especially at high/rapid doses), loss of deep tendon reflexes (early sign of toxicity) - **Overdose**: Loss of patellar reflex (plasma Mg ~3.5–5 mmol/L), respiratory paralysis (~5–7.5 mmol/L), cardiac arrest (>7.5 mmol/L) ## Key Drug Interactions - **Neuromuscular blockers (NMBs)**: Enhanced and prolonged blockade. - **Calcium channel blockers**: Additive hypotension and bradycardia. - **Digoxin**: Risk of bradyarrhythmias (especially with hypokalemia/hypomagnesemia). - **Loop/thiazide diuretics**: Increase Mg loss (hypomagnesemia). ## Monitoring - **Baseline & serial**: Serum magnesium, calcium, potassium, renal function. - **During infusion**: Deep tendon reflexes, respiratory rate, blood pressure, ECG (if arrhythmia indication). Level monitoring every 6–12 h during continuous infusion. Target therapeutic range varies: 2–3.5 mmol/L for pre-eclampsia; 0.7–1.0 mmol/L for replacement. - **Toxicity**: Stop infusion if reflexes absent, RR <12/min, or hypotension not responsive. ## Clinical Pearls - **Antidote for toxicity**: IV calcium gluconate 1 g (10 mL of 10%) over 3–5 min – reverses respiratory/cardiac depression. - **IV compatibility**: Incompatible with solutions containing calcium, phosphate, bicarbonate; do not co-administer in same line. - **Pain at injection site**: Common with IM use; give deep IM, consider lidocaine. - **Oral magnesium**: Poorly absorbed; used primarily for constipation or long-term replacement (renal excretion governs levels, not dose alone). *Educational disclaimer: This information is for clinical education and reference only. Dosing and safety recommendations may vary by region and patient population. Always verify current prescribing information, local protocols, and product monograph before administration.*