magnesium sulphate: risk of skeletal adverse effects in the neonate following prolonged or repeated use in pregnancy

Last edited 05/2019 and last reviewed 06/2023

Magnesium sulfate: risk of skeletal adverse effects in the neonate following prolonged or repeated use in pregnancy

• maternal administration of magnesium sulfate for longer than 5-7 days in pregnancy has been associated with skeletal adverse effects and hypocalcaemia and hypermagnesemia in neonates
  
  
• if use of magnesium sulfate in pregnancy is prolonged or repeated, consider monitoring of neonates for abnormal calcium and magnesium levels and skeletal adverse effects

Previous safety concerns about prolonged use of magnesium sulfate in pregnancy

• in 2013 the US FDA issued a safety communication recommending against use of magnesium sulfate for more than 5-7 days when used as a tocolytic (not an authorised indication in the UK)
  • such prolonged exposure may result in significantly higher cumulative doses than those encountered with use of magnesium sulfate in the UK for eclampsia or foetal neuroprotection
    
    
• the US FDA alert was based on 4 reports of fractures and 35 reports of osteopenia or radiographical bone abnormalities in neonates, some of which also describe hypocalcaemia and hypermagnesemia in the neonate. The long-term clinical significance of the biochemical and skeletal effects is unknown, with the available evidence suggesting a transient effect
  
  
• although overall, most clinically relevant cases were seen following high doses of magnesium sulfate over prolonged periods, the MRHA are aware of reports in the literature of electrolyte imbalances in the neonate following lower doses or after treatment periods of less than 5 days (for example, clinically significant hypocalcaemia in a neonate following cumulative administration of an estimated 100 grams of magnesium sulfate)

Reference:

• MRHA. Drug Safety Update volume 12, issue 10: May 2019: 3.