Magnesium sulfate (magnesium sulphate)

Mineral • anticonvulsant • antiarrhythmic • bronchodilator

⚕️ Intended for medical professionals • Review full product labeling and local protocols
Toxicity Neuroprotection References
THE INFORMATION IN THE OBRx™ IS INTENDED SOLELY FOR USE BY THE MEDICAL PROFESSION.
It is not intended for lay persons.
Caution: Parenteral use in renal insufficiency may cause magnesium intoxication. Contraindicated in heart block, myocardial damage, and myasthenia gravis.

Treatment of preeclampsia and eclampsia [1–3,12,13]

Regimens formatted for mobile readability; clinical content retained.

Continuous intravenous infusion

4–6 g loading dose diluted in 100 mL over 15 min → 1–2 g/hr infusion. Stop 24 hr postpartum or after last seizure.

Intermittent intramuscular injections

4 g IV (20% solution) ≤1 g/min → 5 g IM (50% solution) in each buttock. Then 5 g IM q4h alternating sides. Use 20 gauge 3-inch needle.

For recurrent convulsions

  • Give up to 2 g IV (20% solution) ≤1 g/min.
  • If ≥70 kg → additional 2 g may be given slowly.

Continue magnesium ONLY if

  • RR > 16/min
  • Urine output > 25 mL/hr
  • Patellar reflexes intact

If urine output <100 mL in 4 hr → reduce dose (IM 2.5 g or IV 0.5 g/hr). Measure serum magnesium every 4 to 6 hours if serum creatinine is >= 1 mg/dL [1]

Magnesium level monitoring [1,3,4]

Serum magnesium thresholds and clinical effects (table scrolls on small screens).
Serum magnesium Effect
> mmol/L mEq/L mg/dL
2–3.5 4–7 5–9 Therapeutic
>3.5 >7 >9 Loss of reflexes
>5 >10 >12 Respiratory paralysis
>12.5 >25 >30 Cardiac arrest

Management of toxicity

Formatted for quick bedside scanning; content retained.

If reflexes depressed but breathing normal → hold magnesium and check level.

If respiratory depression:

  • Stop magnesium, give oxygen, administer Calcium gluconate 10 mL of 10% IV over 10 min [5].

Reminder: Adjust for renal impairment per protocol; monitor urine output and reflexes.

Antenatal neuroprotection

Text retained; regimens separated for readability.

Fetal exposure to magnesium sulfate in women at risk of preterm delivery appears to reduce the risk of cerebral palsy. The appropriate total dosage, infusion period, need for retreatment, and therapeutic window for neuroprotection are not known [14,15].

Regimen A

Loading dose of 4 g by infusion pump over 30 minutes, followed by continuous intravenous infusion at 1 g per hour until birth. Magnesium sulfate should be discontinued if delivery is no longer imminent or a maximum of 24 hours of therapy has been administered [16].

Regimen B

Loading dose of 6 g by infusion pump over 20 to 30 minutes, followed by continuous intravenous infusion at 2 g per hour. Discontinue infusion after 12 hours if delivery is no longer considered imminent. If threat of delivery recurs after 6 or more hours, then repeat-bolus [6].

Torsades de Pointes [7]

Associated with VF/pulseless VT — treat hypokalemia if present.

Associated with VF/pulseless VT

1–2 g in 10 mL D5W IV/IO over 5–20 min.

With pulses

1–2 g in 50–100 mL D5W IV over 5–60 min.

Severe acute asthma [7,8]

Adjunct therapy dosing (legacy).

1.2–2 g IV over 20 minutes.

Hypomagnesemia [9,10]

Severe vs mild regimens (legacy).

Severe (<1 mEq/L)

2 g in 100 mL D5W over 5–10 min → 4–6 g/day for 3–5 days.

Mild (1.1–1.4 mEq/L)

6–12 g/day × 3–5 days after stores replenished.

Supplied as

How supplied section retained; formatted for clarity.

Magnesium sulfate 50% (5 g/10 mL = 4 mEq/mL) must be diluted to ≤20% before IV infusion.

UPDATED 12/4/2025

References

Collapsible references (as provided).
References (click to expand) ▾

References

  1. Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Rouse DJ, Spong CY. Pregnancy Hypertension. In: Williams Obstetrics. 23rd ed. New York: McGraw-Hill; 2010:737.
  2. Which anticonvulsant for women with eclampsia? Evidence from the Collaborative Eclampsia Trial. Lancet. 1995;345(8963):1455–1463.
  3. Duley L. Magnesium sulphate regimens for women with eclampsia: messages from the Collaborative Eclampsia Trial. Br J Obstet Gynaecol. 1996 Feb;103(2):103–105. PMID: 8616123
  4. Lu JF, Nightingale CH. Magnesium sulfate in eclampsia and pre-eclampsia: pharmacokinetic principles. Clin Pharmacokinet. 2000 Apr;38(4):305–314. PMID: 10803454
  5. Royal College of Obstetricians and Gynaecologists. RCOG Guideline number 10(A): The Management of Severe Pre-eclampsia/Eclampsia. March 2006. Link (Accessed 7/16/2010).
  6. Rouse DJ, et al.; NICHD MFMU Network. Magnesium sulfate for prevention of cerebral palsy. N Engl J Med. 2008 Aug 28;359(9):895–905. PMID: 18753646
  7. ECC Committee, AHA. 2005 AHA Guidelines for CPR and ECC. Circulation. 2005;112(24 Suppl):IV1–203. PMID: 16314375
  8. Rowe BH, et al. Magnesium sulfate for treating acute asthma exacerbations. Cochrane Database Syst Rev. 2000;(2):CD001490.
  9. Martin KJ, et al. Clinical consequences and management of hypomagnesemia. J Am Soc Nephrol. 2009 Nov;20(11):2291–2295. PMID: 18235082
  10. Gnerlich JL, Buchman TG. Fluids, Electrolyte, and Acid-Base Disorders. In: Klingensmith ME, et al., eds. The Washington Manual of Surgery. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2008:82.
  11. Package insert. Magnesium sulfate injection. Hospira, Inc. May 2010. (Legacy dailymed link removed per prior preference.)
  12. Cahill AG, et al. Magnesium for seizure prophylaxis in mild preeclampsia. Obstet Gynecol. 2007 Sep;110(3):601–607. PMID: 17766606
  13. Alexander JM. Selective magnesium sulfate prophylaxis for prevention of eclampsia. Obstet Gynecol. 2006 Oct;108(4):826–832. PMID: 17012442
  14. Costantine MM. Antenatal magnesium sulfate neuroprotection meta-analysis. Obstet Gynecol. 2009 Aug;114(2 Pt 1):354–364. PMID: 19622997
  15. ACOG Committee Opinion No. 455; SMFM. Magnesium sulfate before anticipated preterm birth for neuroprotection. Obstet Gynecol. 2010 Mar;115(3):669–671. PMID: 20177305
  16. Magee L, et al. SOGC guideline: magnesium sulphate for fetal neuroprotection. J Obstet Gynaecol Can. 2011 May;33(5):516–529. PMID: 21639972
  17. Doyle LW, et al. School-age outcomes after antenatal magnesium sulfate vs placebo. JAMA. 2014 Sep 17;312(11):1105–1113. PMID: 25226476