Magnesium Sulfate

Drug Levels and Effects:

Summary of Use during Lactation:

Although intravenous magnesiumsulfategiven prior to delivery might affect the infant's ability to breastfeed, it increases milk magnesium concentrations only slightly. Oral absorption of magnesium by the infant is poor, so maternal magnesium therapy is not expected to affect the breastfed infant's serum magnesium. Magnesiumsulfatecan be taken during breastfeeding and no special precautions are required

Drug Levels:

Maternal Levels.

Ten women with pre-eclampsia were given 4 grams of magnesiumsulfateintravenously followed by 1 gram per hour until 24 hours after delivery. While the average serum magnesium was 35.5 mg/L in treated women compared to 18.2 mg/L in 5 untreated controls, colostrum magnesium levels at the time of discontinuation of the infusion was 64 mg/L in treated women and 48 mg/L in the controls. By 48 hours after discontinuation, colostrum magnesium levels were only slightly above control values and by 72 hours they were virtually identical to controls.[1]

Infant Levels.

Relevant published information was not found as of the revision date.

Effects in Breastfed Infants:

Fifty mothers who were in the first day postpartum received 15 mL of either mineral oil or an emulsion of mineral oil and another magnesium salt, magnesium hydroxide equivalent to 900 mg of magnesium hydroxide, although the exact number who received each product was not stated. Additional doses were given on subsequent days if needed. None of the breastfed infants were noted to have any markedly abnormal stools, but all of the infants also received supplemental feedings.[2]

Possible Effects on Lactation:

One mother who received intravenous magnesiumsulfatefor 3 days for pregnancy-induced hypertension had lactogenesis II delayed until day 10 postpartum. No other specific cause was found for the delay, although a complete work-up was not done.[3] A subsequent controlled clinical trial found no evidence of delayed lactation in mothers who received intravenous magnesiumsulfatetherapy.[4] Some, but not all, studies have found a trend toward increased time to the first feeding or decreased sucking in infants of mothers treated with intravenous magnesiumsulfateduring labor because of placental transfer of magnesium to the fetus.[4][5]

Alternate Drugs to Consider:

(Laxative) Docusate,Magnesium Hydroxide,Psyllium,Sodium Picosulfate,Sodium Phosphate


1. Cruikshank DP , Varner MW, Pitkin RM. Breast milk magnesium and calcium concentrations following magnesiumsulfatetreatment. Am J Obstet Gynecol. 1982;143:685-8. PMID:7091241
2. Baldwin WF. Clinical study of senna administration to nursing mothers.:assessment of effects on infant bowel habits. Can Med Assoc J. 1963;89:566-7. PMID:14045350
3. Haldeman W. Can magnesiumsulfatetherapy impact lactogenesis? J Hum Lact. 1993;9:249-52. PMID:8260059
4. Riaz M, Porat R et al. The effects of maternal magnesiumsulfatetreatment on newborns: a prospective controlled study. J Perinatol. 1998;18:449-54. PMID:9848759
5. Rasch DK, Huber PA et al. Neurobehavioral effects of neonatal hypermagnesemia. J Pediatr. 1982;100:272-6. PMID:7199083

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Anti-Arrhythmia Agents

  • Anticonvulsants

  • Cathartics

  • Gastrointestinal Agents

  • Magnesium Compounds

  • Tocolytic Agents

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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