Magnesium Sulfate

Magnesium sulphate taken intravenously is used to treat certain arrythmias, eclampsia and convulsions of newborns and infants, orally as an osmotic laxative and in the prophylaxis of migraine ^{(Pringsheim 2012)} and,topically for certain types of skin inflammation.

Since the last update we have not found any published data on its excretion in breast milk.  

Magnesium is a natural component of milk. The average natural concentration of magnesium in milk is 31 mg/L (15 to 64 mg/L). ^{(Dórea 2000, Feeley 1983)}

Daily magnesium requirements for breastfeeding mothers are estimated at 310 to 360 mg ^{(MedlinePlus 2017EFSA 2006)}; some countries have established figures of up to 450 mg daily. ^{(Hall 2010)}

Ingested magnesium is not concentrated in breastmilk. Its concentration in milk is very stable and depends little on diet ^{(Dórea 2000)} and other factors, including intravenous administration of magnesium sulphate to the mother: the levels of magnesium in milk of mothers treated with intravenous magnesium sulphate were 6.4 mg/L versus 4.8 mg/L in untreated patients ^{(Dorea 2000, Cruikshank 1982)}, a clinically non-significant difference for the infant, which also disappeared within a few hours.

Its low oral bioavailability hinders transfer to plasma and, therefore, to breastmilk, as well as transfer to infant plasma via breastmilk. ^{(Morris 1987)}

In women treated with magnesium sulphate before or during labour, a delay in milk production or lactogenesis II has been observed, directly proportional to the duration of magnesium infusion: greater with 24 hours than with 6 to 8 hours ^{(Solly 2026, Saha 2025, Mushtaq 2023, Vigil 2018 and 2019, Haldeman 1993).} and less frequency of breastfeeding ^{(Kuriloff 2023, Meier 2005)} as well as hypotonia in newborns ^{(Riaz 1998, Rasch 1982)}, which could interfere with adequate breast stimulation, but this can be counteracted by a firm decision by the mother and effective support for her. ^{(Cordero 2012)}

Various medical associations and expert consensus consider the use of various magnesium salts to be safe during breastfeeding ^{(Hale 2019, Briggs 2015, Dennis 2012, Schaefer 2007, Mahadevan 2006, Richter 2005, Nice 2000, Broussard 1998, Idama 1998)}. American Academy of Pediatrics: medication usually compatible with breastfeeding ^{(AAP 2001)}. List of WHO essential medicines: compatible with breastfeeding. ^(WHO 2002)

If the intravenous administration of magnesium sulphate is considered compatible with breastfeeding, all the more reason that salts administered orally will also be compatible. ^{(Hagemann 1998)}