Prolonged or repeated use of magnesium sulfate in pregnancy linked to risk of skeletal adverse effects in infants

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Magnesium sulfate indicated for prevention of further seizures associated with eclampsia in pregnancy and for treatment of magnesium deficiency in hypomagnesemia.

The NICE guideline Preterm labour and birth (NG25) advises offering IV magnesium sulfate for foetal neuroprotection in women in preterm labour or having a planned preterm birth within 24 hours, who are between 24 and 29 weeks and 6 days of pregnancy or having a preterm birth between 30 and 33 weeks and 6 days of pregnancy.

The dose recommended by NICE, if given for a full 24 hours, equates to 28 g of magnesium sulfate, equivalent to usual minimum dose in eclampsia. However, new advice should be considered in case uncertainty around the exact timing of delivery results in repeat administration.

In 2013 the US FDA issued a safety communication recommending against the use of magnesium sulfate for more than 5-7 days when used as a tocolytic. 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.

Although overall, most clinically relevant cases were seen after high doses of magnesium sulfate over prolonged periods, there are reports of electrolyte imbalances in neonates following lower doses or after treatment periods of less than 5 days in literature.

The MHRA is not aware of any reports in the UK of skeletal adverse effects or relevant biochemical effects in neonates following use of magnesium sulfate for foetal neuroprotection. However, following efforts to achieve increased uptake in preterm labour and birth (including through the PReCePT project), data suggests usage is increasing in the UK. Healthcare professionals should, therefore, be vigilant for any adverse effects in neonatal period if in-utero exposure to magnesium sulfate is prolonged.

Healthcare professionals are advised to consider monitoring neonates for abnormal calcium and magnesium levels and skeletal adverse effects if maternal treatment with magnesium sulfate is prolonged or repeated beyond current recommendations.

Healthcare professionals are advised to report suspected adverse drug reactions to magnesium sulfate after exposure during pregnancy via the Yellow Card Scheme.