Magnesium Sulfate

Magnesium sulfate is a magnesium salt. The injection is a hospital medicine used to treat low magnesium and to prevent and control seizures in pre-eclampsia and eclampsia. Doctors also use it in selected cases of severe asthma. A separate oral form is sold as a saline laxative for occasional constipation. Injectable magnesium sulfate must be given by trained healthcare professionals with appropriate monitoring. It is not a self-treatment. This guide covers magnesium sulfate uses, dosage, side effects, precautions, drug interactions, use in pregnancy and breastfeeding and its approximate price in India.

Magnesium Sulfate at a Glance

What Is Magnesium Sulfate and How Does It Work?

Magnesium sulfate injection replaces magnesium when levels are too low and is used to prevent and control seizures in pre-eclampsia and eclampsia. Taken by mouth in larger amounts, it acts as a saline laxative. The injection and the oral product are different medicines with different doses and risks.

Uses of Magnesium Sulfate

• Low magnesium (hypomagnesemia): the US injection label lists magnesium deficiency, especially acute low magnesium with tetany (muscle spasms).
• Intravenous nutrition: the label lists addition to total parenteral nutrition to correct or prevent low magnesium.
• Pre-eclampsia and eclampsia: the label lists prevention and control of seizures. UK NICE guidance recommends intravenous magnesium sulfate for women in a critical care setting with severe hypertension or severe pre-eclampsia who have had an eclamptic fit, and says to consider it in some women with severe pre-eclampsia, such as when birth is planned within 24 hours.
• Severe asthma: not a labelled use on the US injection label. Clinicians may use a single intravenous dose in selected severe exacerbations that have not responded adequately to initial treatment. This is protocol and guidance based, and it is not self-treatment.
• Occasional constipation: the oral form, such as Epsom salt, is labelled in the US for this use.

Magnesium Sulfate Dosage and Administration

The doses below are examples from the sources named. They are not interchangeable between products, countries or settings, and they are not instructions for patients. Injectable magnesium sulfate is given only by trained healthcare professionals, with appropriate monitoring. Doses depend on the condition, age, weight, kidney function and response.

Low magnesium, adults (US label: Magnesium Sulfate Injection, USP 50%, Hospira)

• Mild deficiency: 1 g (2 mL of the 50% solution) injected into a muscle. The label lists this as every six hours for four doses.
• Severe deficiency: as much as 250 mg per kg into a muscle within four hours, or 5 g added to one litre of 5% dextrose and given as a slow intravenous infusion over three hours.

Pre-eclampsia and eclampsia

US label (Hospira 50%):

• Total initial dose 10 to 14 g: for example 4 to 5 g in 250 mL of 5% dextrose intravenously, plus up to 10 g into the muscles (5 g in each buttock). Then 4 to 5 g into the muscle every four hours as needed. The label also says some clinicians give 1 to 2 g per hour by continuous intravenous infusion.
• Treatment continues until the seizures stop. The total in 24 hours should not exceed 30 to 40 g. With severe kidney impairment the label maximum is 20 g in 48 hours.

UK NICE (NG133, recommendation 1.8.4):

• A 4 g intravenous loading dose over 5 to 15 minutes, then an infusion of 1 g per hour for 24 hours. After an eclamptic fit, the infusion continues for 24 hours after the last fit. Recurrent fits are treated with a further 2 to 4 g intravenously over 5 to 15 minutes.
• NICE says not to use diazepam, phenytoin or other anticonvulsants instead of magnesium sulfate for eclampsia.

Severe asthma (clinical settings; not on the US label)

A single hospital protocol is not a universal standard. Patients should not be discharged straight after treatment in the adult protocol.

Children (US label)

The US label has no separate paediatric section. It says the 50% solution should be diluted to 20% or less for injection into a muscle in infants and children.

Oral Epsom salt (US OTC label, revised 02/2026)

These are examples from a US label, not recommendations for Indian products. The label directs adults and children 12 and older to take 2 to 6 level teaspoons (10 to 30 g) daily, and children 6 to under 12 to take 1 to 2 level teaspoons (5 to 10 g) daily, dissolved in 8 ounces of water, with a full glass of liquid. For children under 6, consult a doctor. It generally produces a bowel movement in 1/2 to 6 hours.

Take this medicine only as advised by your doctor or healthcare professional. Do not start, stop, or change the dose on your own.

Monitoring

Monitoring depends on the indication, the person’s condition and the protocol. The US label describes checking the knee-jerk reflex and breathing rate before repeat doses and keeping adequate urine output. It also describes checking magnesium levels in people with severe kidney impairment. The label says reflexes can be lost at high magnesium levels, where respiratory paralysis is a risk. For children with asthma, the Birmingham guide describes continuous cardiac monitoring during infusion and observation afterward. The NICE sections reviewed did not specify a maternal monitoring schedule, so the treating team follows local protocol.

Side Effects and Magnesium Toxicity

The US label says the adverse effects of injected magnesium usually result from magnesium intoxication. Reported effects include flushing, sweating, low blood pressure, depressed reflexes, flaccid paralysis, low body temperature, circulatory collapse, and heart and central nervous system depression progressing to respiratory paralysis.

Urgent clinical assessment is needed for loss of reflexes, severe weakness, very low blood pressure, slow or shallow breathing, or heart symptoms. For overdose, the label says breathing support must be provided until a calcium salt can be injected intravenously. It also says an injectable calcium salt should be immediately available when magnesium sulfate is used in eclampsia. Frequencies were not established in the sources reviewed, so none are given here.

Magnesium Sulfate Contraindications and Precautions

Formal contraindication (US injection label): parenteral use in patients with heart block or myocardial damage.

Precautions:

• Kidney impairment: parenteral use may lead to magnesium intoxication, and dose limits apply.
• Older adults: the label notes that older patients often need reduced doses.
• Aluminum: the product contains aluminum that may be toxic, particularly with prolonged use in impaired kidney function and in premature newborns.
• Newborns exposed in pregnancy: the label notes magnesium toxicity can occur in neonates after prolonged IV use for eclampsia.

Magnesium Sulfate Drug Interactions

• CNS depressants (barbiturates, narcotics, hypnotics, systemic anaesthetics): additive depression, so doses are adjusted cautiously.
• Neuromuscular blocking agents: excessive neuromuscular block has occurred, so use with caution.
• Cardiac glycosides such as digoxin: use with extreme caution, because calcium given to treat magnesium toxicity may cause heart block.
• Specific antibiotics: the label lists, under incompatibilities, that magnesium may reduce the antibiotic activity of streptomycin, tetracycline and tobramycin. This does not apply to all antibiotics.
• IV admixtures: the label lists incompatibilities (precipitation) with calcium, phosphates, carbonates and bicarbonates, among others.

Tell your doctor or pharmacist about all prescription medicines, OTC medicines, supplements and herbal products you use. This list is not complete.

Magnesium Sulfate in Pregnancy and Breastfeeding

• Pregnancy: the US label says continuous administration beyond 5 to 7 days to pregnant women can lead to low calcium and bone abnormalities in the baby, and that the shortest duration that can lead to fetal harm is not known. NICE notes the MHRA warning on neonatal skeletal effects, low calcium and high magnesium with use beyond 5 to 7 days. It advises considering newborn calcium and magnesium checks if use is prolonged or repeated. This does not mean every short course is harmful, and 5 to 7 days is not a safe limit. Duration and newborn monitoring depend on the clinical situation.
• Breastfeeding: the label says magnesium is distributed into milk during parenteral treatment and advises caution. For the oral laxative, the US label says to ask a health professional first if pregnant or breastfeeding.

Magnesium Sulfate Brands and Price in India

Only two listings were found. Both are undated, and both were shown as unavailable. Prices below are unverified listings, not current prices, and no price range is given.

The strength is the concentration (50%) and not the total amount in the pack. The injection is given by a doctor or nurse and should not be bought or self-injected.

How HealthPil Can Help

Medicines should be started, adjusted, or stopped only under the guidance of a qualified healthcare professional. If you have questions about this medicine, its side effects, or your treatment plan, you can consult a doctor through HealthPil.