Magnesium Sulfate
Magnesium sulfate
Brand names:Generic
An electrolyte and physiologic calcium antagonist used in eclampsia and severe pre-eclampsia (prevention and treatment of seizures), refractory bronchospasm, torsades de pointes, hypomagnesemia, and digitalis toxicity. Magnesium sulfate has multiple mechanisms producing smooth muscle relaxation, membrane stabilization, and CNS depression.
Pharmacology and Actions
Competitively antagonizes calcium at neuromuscular junctions and in vascular and bronchial smooth muscle, producing relaxation. Stabilizes excitable membranes in cardiac and neurologic tissue, suppressing ectopy and seizure activity. Blocks NMDA glutamate receptors in CNS, contributing to anticonvulsant effect. Increases nitric oxide release and modulates inflammatory mediators. Cofactor for over 300 enzymatic reactions; deficiency contributes to cardiac arrhythmia, neuromuscular hyperexcitability, and metabolic dysfunction.
Indications
- Eclampsia: prevention and treatment of seizures in pregnancy
- Severe pre-eclampsia with seizure prevention
- Refractory asthma exacerbation not responding to bronchodilators and steroids
- Torsades de pointes (polymorphic ventricular tachycardia with QT prolongation)
- Hypomagnesemia symptomatic or severe
- Hypokalemic refractory to potassium replacement (magnesium repletion often required for potassium correction)
- Digitalis toxicity adjunct
- Tocolysis in preterm labor (historical, mostly replaced by other agents)
Absolute Contraindications
- Heart block (relative; magnesium prolongs PR interval)
- Myasthenia gravis (potentiates neuromuscular weakness)
- Severe renal impairment without dose adjustment
- Hypocalcemia (relative; magnesium worsens calcium-related effects)
Precautions and Side Effects
Flushing, warmth, sweating common with IV administration. Hypotension with rapid push. Respiratory depression at toxic levels (above 5 mmol/L). Loss of deep tendon reflexes at moderately elevated levels (signals approaching toxicity). Cardiac conduction delays (PR prolongation, bradycardia, asystole at high levels). Hypocalcemia. Hypothermia. Nausea, vomiting. Antidote for severe toxicity: calcium gluconate 1 g IV.
Adult Dosing
Pediatric Dosing
Asthma: 25 to 50 mg/kg IV (max 2 g) over 20 minutes. Torsades: 25 to 50 mg/kg IV (max 2 g) over 1 to 2 minutes. Pediatric eclampsia is rare; consult obstetric protocols.
Pharmacokinetics
Peak Effect: 30 minutes to 1 hour IV
Duration: 30 minutes to 6 hours depending on dose and indication
Storage and Handling
Room temperature 15 to 30 degrees C. Pre-mixed bags (2 g in 50 mL or 100 mL NS) and 50% solution ampules and vials (5 g in 10 mL) standard. Shelf life 2 to 3 years. Compatible with most IV fluids; some incompatibilities exist (avoid mixing with carbonate or phosphate solutions).
Reconstitution:
50% solution (500 mg/mL) is concentrated; do not give undiluted as IV push (causes severe hypotension). Dilute in NS, LR, or D5W per indication: 2 g in 50 to 100 mL for IV piggyback; loading and continuous infusion doses typically pre-mixed at pharmacy. IM route uses 50% solution directly (10 g in 20 mL).
TCCC and TECC Role
Not a core TCCC trauma medication. Standard component of EMS, critical care, and hospital protocols for the indications above. Tactical EMS providers carrying expanded ALS formularies include magnesium for refractory asthma and torsades de pointes management.
Magnesium sulfate is the second-line drug that becomes first-line in specific scenarios. For eclampsia in a pregnant patient with seizure, magnesium beats every benzodiazepine and is the standard of care. For an asthmatic who is failing albuterol, ipratropium, and steroids, magnesium 2 g IV is the next step before considering intubation. For torsades de pointes, magnesium is the answer even if the magnesium level is normal. The IM route for eclampsia exists for resource-limited environments where IV access is delayed. Operational practitioners outside obstetrics may not see eclampsia often, but the pregnant patient with seizure in the prehospital environment requires magnesium recognition and administration.
Using benzodiazepines as primary therapy for eclampsia. Magnesium is the standard of care and should be administered concurrently with airway management. Benzodiazepines treat the seizure symptom but do not address the underlying pre-eclamptic process; magnesium does both. The other common mistake is failing to monitor for magnesium toxicity during continuous infusion: loss of deep tendon reflexes is the bedside warning sign that should prompt level checking and dose reduction.
This drug profile is provided as educational reference material for trained medical providers. It is not medical advice, not a substitute for formal training, and not a substitute for current published guidelines or medical direction.
Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances are subject to additional handling, accountability, and documentation requirements per DEA and state law. Always verify dosing, indications, contraindications, and route of administration against current published guidelines and your local protocols before administration.
If this content is being viewed during a medical emergency, call 911 immediately and follow the direction of your local emergency dispatch and medical control. Do not use this reference as a substitute for emergency medical services.
Drug information evolves. Last reviewed dates and source citations are provided for each entry. Confirm currency against the cited source before clinical use.
Penn Tactical Solutions publishes this reference for educational purposes. PTS does not provide medical direction and does not assume responsibility for clinical decisions made in the field. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Educational reference for trained medical providers. Not medical advice. Not a substitute for formal training, current published guidelines, or medical direction. Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances require additional storage, accountability, and documentation per DEA and state law.
In a medical emergency, call 911. This reference is not a substitute for emergency medical services.
Verify dosing, indications, and contraindications against current published guidelines and your local protocols before administration. Confirm content currency against the source citation. Penn Tactical Solutions does not provide medical direction. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Magnesium Sulfate
| IV/IO | Eclampsia: 4 to 6 g IV loading dose over 15 to 20 minutes, followed by 1 to 2 g/hr continuous infusion for 24 hours after delivery or last seizure. Refractory asthma: 2 g IV over 20 minutes (single dose). Torsades: 2 g IV over 1 to 2 minutes for stable patient; 2 g IV push for pulseless torsades. Severe hypomagnesemia: 1 to 2 g IV over 60 minutes, may repeat based on symptoms and level. (Immediate (within 1 minute for cardiac effects)) |
| IM | 10 g IM (5 g in each buttock) for eclampsia in austere settings without IV access. Painful; reserved for situations where IV access is not immediately feasible. (1 hour) |
| IN | None (None) |
| PO | Oral magnesium oxide, citrate, or other salts available for chronic hypomagnesemia and laxative use; not used for acute conditions. (1 to 2 hours (oral magnesium for chronic deficiency)) |