bronchodilator saba

Magnesium Sulfate

Various

Route: IV · IM (for eclampsia when no IV access)
Onset: 20–30 minutes (IV for bronchodilation)
Duration: 30–60 minutes

Mechanism of action

Divalent cation. Physiological calcium antagonist in smooth muscle → inhibits calcium-mediated bronchoconstriction → bronchodilation. Also inhibits mast cell and T-lymphocyte activation. Reduces neuromuscular transmission at high doses.

Dosing

Adult: Severe asthma: 2 g IV over 20 min (single dose). May repeat. IV infusion: 1–2 g/hr for eclampsia
Pediatric: Severe asthma: 25–75 mg/kg IV over 20 min (max 2 g)

Indications

Severe/refractory acute asthma (adjunct to inhaled bronchodilators and steroids)
Pre-eclampsia and eclampsia (seizure prophylaxis/treatment)
Torsades de pointes (cardiac arrhythmia)
Hypomagnesemia

Contraindications

Renal failure (impaired excretion → toxicity)
Heart block
Myasthenia gravis
Hypermagnesemia

Side effects

Flushing / warmth
Hypotension
Loss of deep tendon reflexes (first sign of toxicity)
Respiratory depression (toxicity — levels >5 mg/dL)
Cardiac arrest (severe toxicity — levels >10–15 mg/dL)
Nausea

Monitoring parameters

Deep tendon reflexes (disappear first — DTR loss = early toxicity)
Respiratory rate (depression = dangerous toxicity)
Serum magnesium levels (therapeutic 4–7 mg/dL for eclampsia; 2–4 mg/dL bronchodilation)
Urine output (required for excretion — minimum 25–30 mL/hr)
Blood pressure

Drug interactions

Calcium gluconate (antidote for toxicity)
Neuromuscular blockers (potentiated — reduced dose needed)
Digoxin (hypermagnesemia may cause toxicity)

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