Magnesium sulfate (medical use)
Magnesium sulfate heptahydrate
|Trade names||Epsom salt, others|
|Main uses||Eclampsia, low blood magnesium|
|IV, IM, by mouth, topical|
|Defined daily dose||3 to 7 grams by mouth, and 1 gram by injection.|
|Chemical and physical data|
|Formula||MgSO4 - 7H2O|
|3D model (JSmol)|
Magnesium sulfate as a medication is used to treat and prevent low blood magnesium and seizures in women with eclampsia. It is also used in the treatment of torsades de pointes, severe asthma exacerbations, constipation, and barium poisoning. It is given by injection into a vein or muscle as well as by mouth. As epsom salts, it is also used for mineral baths.
Common side effects include low blood pressure, skin flushing, and low blood calcium. Other side effects may include vomiting, muscle weakness, and decreased breathing. While there is evidence that use during pregnancy may harm the baby, the benefits in certain conditions are greater than the risks. Its use during breastfeeding is deemed to be safe. Magnesium sulfate for medical use is the magnesium sulfate heptahydrate salt. The way it works is not fully understood, but is believed to involve depressing the action of neurons.
Magnesium sulfate came into medical use at least as early as 1618. It is on the World Health Organization's List of Essential Medicines. The wholesale cost in the developing world is about US$0.35–8.73 per 10 ml of 50% solution. In the United Kingdom 4 ml of 20% solution costs the NHS about 10.23 pounds. In the United States a course of medication typically costs less than $25.
Magnesium sulfate can be given by mouth, respiratory, or intravenous routes.
Magnesium sulfate may be used as bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma, The salt can be administered by nebulization or by intravenous injection.
Magnesium sulfate is effective in decreasing the risk that pre-eclampsia progresses to eclampsia. Intravenous magnesium sulfate is used to prevent and treat seizures of eclampsia. It reduces the systolic blood pressure but does not alter the diastolic blood pressure, so the blood perfusion to the fetus is not compromised. It is also commonly used for eclampsia where compared to diazepam or phenytoin it results in better outcomes.
Magnesium sulfate was once used as a tocolytic, but meta-analyses have failed to support it as an anti-contraction medication. Usage for prolonged periods (more than five to seven days) may result in health problems for the baby.
In those at risk of an early delivery, magnesium sulfate appears to decrease the risk of cerebral palsy. It is unclear if it helps those who are born at term. Guidelines for the use of magnesium sulfate in mothers at risk of preterm labour are not strongly adhered to.
Magnesium sulfate was historically used as a treatment for lead poisoning. Prior to the development of chelation therapy, cases of accidental lead ingestion were often immediately treated with magnesium sulfate, which would cause the lead to be precipitated out and, with a high enough dose, literally purged from the digestive system. In this application, magnesium sulfate saw particular use in veterinary medicine of the early-to-mid 20th century; Epsom salt was already available on many farms for agricultural purposes, and it was often prescribed in the treatment of farm animals which inadvertently ingested lead.
Epsom salt baths have been claimed to also soothe and hasten recovery of muscle pain, soreness, or injury. However, these claims have not been scientifically confirmed. The solubility of magnesium sulfate water is inhibited by lipids in lotions resulting in variable absorption rates when applied to the skin. Temperature and concentration are also factors.
In the UK, a medication containing magnesium sulfate, called "drawing paste", is claimed to be useful for small boils or localised infections. The standard British Pharmacopoeia composition is dried magnesium sulfate 47.76% (by mass), phenol 0.49%, and glycerol to balance.
The defined daily dose is 3 to 7 grams by mouth, and 1 gram by injection. For preeclampsia or eclampsia it is generally given as a 4 gram dose over 15 minutes followed by 1 gram per hour. If seizures occur again 2 to 4 more grams may be given.
A 1 gram dose of magnesium sulfate is the same as 4 mmol or 8 mEq of magnesium.
An abnormally elevated plasma concentration of magnesium is called hypermagnesemia.
Magnesium sulfate has been used as an experimental treatment of Irukandji syndrome caused by envenomation by certain species of Irukandji jellyfish, but the efficacy of this treatment remains unproven.
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The treatment of acute lead-poisoning consists in the evacuation of the stomach, if necessary, the exhibition of the sulphate of sodium or of magnesium, and the meeting of the indications as they arrive. The Epsom and Glauber's salts act as chemical antidotes, by precipitating the insoluble sulphate of lead, and also, if in excess, empty the bowel of the compound formed.
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Udall (1) suggests sodium citrate as of some value together with Epsom salts which will bring about a precipitation of the lead in the form of an insoluble compound. Nelson (3) reported a case that survived following the use of a 20% magnesium sulphate solution intravenously, subcutaneously and orally. McIntosh (5) has suggested that purgative doses of Epsom salts may be effective in combining with the lead and overcoming the toxicity.
- Herriot, James (1972). All Creatures Great and Small. New York: St. Martin's Press. p. 157. ISBN 0-312-08498-6.
The specific antidotes to metal poisoning had not been discovered and the only thing which sometimes did a bit of good was magnesium sulphate which caused the precipitation of insoluble lead sulphate. The homely term for magnesium sulphate is, of course, epsom salts.
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