It is not intended for lay persons.
Magnesium sulfate, magnesium sulphate
Mineral, anticonvulsant, antiarrhythmic, bronchodilator
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]
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 if serum creatinine is >= 1mg/dL[1]
Magnesium Level Monitoring [1.,3,4]
| 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
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]
Antenatal Neuroprotection
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 until birth. Magnesium sufate 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
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]
1.2–2 g IV over 20 minutes.
Hypomagnesemia [9,10]
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
Magnesium sulfate 50% (5 g/10 mL = 4 mEq/mL) must be diluted to ≤20% before IV infusion.
UPDATED 12/4/2025
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.
Available at:
http://www.rcog.org.uk/womens-health/clinical-guidance/management-severe-pre-eclampsiaeclampsia-green-top-10a
(Accessed 7/16/2010).
6. Rouse DJ, et al.; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network.
A randomized, controlled trial of magnesium sulfate for the prevention of cerebral palsy.
N Engl J Med. 2008 Aug 28;359(9):895–905.
PMID: 18753646
7. ECC Committee, Subcommittees and Task Forces of the American Heart Association.
2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.
Circulation. 2005 Dec 13;112(24 Suppl):IV1–203. Epub 2005 Nov 28.
PMID: 16314375
Full text:
http://circ.ahajournals.org/content/vol112/24_suppl/
8. Rowe BH, et al. Magnesium sulfate for treating exacerbations of acute asthma in the emergency department.
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. Epub 2008 Jan 30.
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.
Available at:
http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=18492
12. Cahill AG, et al. Magnesium for seizure prophylaxis in patients with mild preeclampsia.
Obstet Gynecol. 2007 Sep;110(3):601–607.
PMID: 17766606
13. Alexander JM. Selective magnesium sulfate prophylaxis for the prevention of eclampsia in women with gestational hypertension.
Obstet Gynecol. 2006 Oct;108(4):826–832.
PMID: 17012442
14. Costantine MM. Effects of antenatal exposure to magnesium sulfate on neuroprotection and mortality in preterm infants: a meta-analysis.
Obstet Gynecol. 2009 Aug;114(2 Pt 1):354–364.
PMID: 19622997
15. American College of Obstetricians and Gynecologists Committee on Obstetric Practice;
Society for Maternal-Fetal Medicine. Committee Opinion No. 455: Magnesium sulfate before anticipated preterm birth for neuroprotection.
Obstet Gynecol. 2010 Mar;115(3):669–671.
PMID: 20177305
16. Magee L, et al. SOGC Clinical Practice Guideline. Magnesium sulphate for fetal neuroprotection.
J Obstet Gynaecol Can. 2011 May;33(5):516–529.
PMID: 21639972
Full guideline:
http://www.sogc.org/guidelines/documents/gui258CPG1106E.pdf
17. Doyle LW, Anderson PJ, Haslam R, Lee KJ, Crowther C; Australasian Collaborative Trial of Magnesium Sulphate (ACTOMgSO4) Study Group.
School-age outcomes of very preterm infants after antenatal treatment with magnesium sulfate vs placebo.
JAMA. 2014 Sep 17;312(11):1105–1113.
doi:10.1001/jama.2014.11189.
PMID: 25226476