magnesium sulfate heptahydrate at a glance
Medicine class
Essential electrolyte and mineral replacement
Hospital uses
Magnesium deficiency and seizure control in severe pre-eclampsia or eclampsia
Epsom Salts uses
Occasional constipation or external relief of pain from sprains, bruises and boils
Administration
Hospital formulations are given by injection or infusion; concentrated solution requires dilution before intravenous use
What is magnesium sulfate heptahydrate used for?
Licensed uses depend on the selected formulation.
Treating proven magnesium deficiency, including low magnesium associated with parenteral nutrition.
Controlling or preventing seizures in severe pre-eclampsia and recurrent seizures in eclampsia.
Epsom Salts crystals: occasional constipation when taken orally.
Epsom Salts crystals: external relief of pain from sprains, bruises and boils.
A well-established non-licensed context is intravenous use before anticipated premature birth for fetal neuroprotection.
How does magnesium sulfate heptahydrate work?
Magnesium is essential for enzyme activity, nerve signalling and muscle contraction. Replacement corrects deficiency. At higher monitored concentrations, it reduces neuromuscular transmission and calcium-dependent excitatory signalling, contributing to its anticonvulsant effect in eclampsia. Oral Epsom Salts retain water in the bowel, producing an osmotic laxative effect.
magnesium sulfate heptahydrate preparations and strengths
Solution for infusion
Route: Intravenous
Strengths: 10% w/v, 20% w/v
Injection
Route: Parenteral
Strengths: 1 g/10 mL, 10% w/v, 20% w/v, 50% w/v
How to take magnesium sulfate heptahydrate
The route and preparation are product-specific.
Injection and infusion formulations must be prepared and administered by trained healthcare professionals.
Concentrated injection or infusion solution must be diluted before intravenous administration; intramuscular injection can be painful.
For constipation, Epsom Salts are taken as a dilute solution. For external use, they are used as a concentrated solution, paste or wet dressing.
Follow pack directions. Do not use Epsom Salts orally in children under 12.
Avoid prolonged laxative use and drink sufficient water, as osmotic laxatives can cause dehydration.
magnesium sulfate heptahydrate side effects
Common or expected effects
- Flushing or feeling hot
- Nausea or vomiting
- Thirst
- Muscle weakness
- Pain, burning or inflammation at an injection site
- Abdominal cramps and watery diarrhoea with oral Epsom Salts
Get urgent medical advice
- Breathing depression or arrest
- Loss of tendon reflexes or profound weakness
- Marked drowsiness, confusion, slurred speech or coma
- Low blood pressure, slow heartbeat or cardiac arrhythmia
- Severe hypersensitivity reaction
- Severe dehydration or paralytic ileus after oral use
magnesium sulfate heptahydrate in pregnancy
Injectable magnesium sulfate may be used under specialist monitoring because severe pre-eclampsia and eclampsia can threaten both mother and baby. Prolonged or repeated exposure has been associated with neonatal calcium, magnesium and skeletal abnormalities, so neonatal monitoring may be needed. The selected Epsom Salts crystal product states that it should not be used during pregnancy.
magnesium sulfate heptahydrate interactions
Tell the clinical team or pharmacist about all prescribed, non-prescription and complementary products.
Neuromuscular blocking medicines
Parenteral magnesium can strengthen and prolong muscle paralysis.
Nifedipine and other calcium-channel blockers
The combination may cause pronounced low blood pressure or other cardiopulmonary effects, requiring close observation.
Common questions about magnesium sulfate heptahydrate
Answers are fully visible for fast scanning and source review.
Is magnesium sulfate heptahydrate the same as Epsom Salts?
Epsom Salts BP contains magnesium sulfate heptahydrate, but it is a crystal product for specified oral or external uses. It must not be substituted for sterile injection or infusion products.
Why is it used in severe pre-eclampsia?
It reduces the risk of an eclamptic seizure and can control seizures if eclampsia occurs. It is given in hospital with close maternal and fetal monitoring.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.