Magnesium (pharmaceutical preparation)
Types of preparations
In practice, magnesium is given in a salt form together with any of several anionic compounds serving as counter-ions, such as chloride or sulfate ('sulphate' in British English). Nevertheless, magnesium is generally presumed to be the active component. An exception is the administration of magnesium sulfate in barium chloride poisoning, where sulfate binds to barium to form insoluble barium sulfate.
Magnesium is absorbed orally at about 30% bioavailability from any water soluble salt, such as magnesium chloride or magnesium citrate. The citrate is the least expensive soluble (high bioavailability) oral magnesium salt available in supplements, with 100 mg and 200 mg magnesium typically contained per capsule or tablet.
Magnesium aspartate, chloride, lactate, citrate and glycinate each have bioavailability 4 times greater than the oxide form and are equivalent to each other per amount of magnesium, though not in price.
The ligand of choice for large-scale manufacturers of multivitamins and minerals containing magnesium is the magnesium oxide due to its compactness, high magnesium content by weight, low cost, and ease-of-use in manufacturing. However it is insoluble in water. Insoluble magnesium salts such as magnesium oxide or magnesium hydroxide (milk of magnesia) depend on stomach acid for neutralization before they can be absorbed, and thus are relatively poor oral magnesium sources, on average.
Magnesium sulfate (Epsom salts) is soluble in water. It is commonly used as a laxative, owing to the poor absorption of the sulfate component. In lower doses, they may be used as an oral magnesium source, however.
Intravenous or intramuscular magnesium is generally in the form of magnesium sulfate solution. Intravenous or intramuscular magnesium is completely bioavailable, and effective. It is used in severe hypomagnesemia and eclampsia.
Indications and uses for administering magnesium include:
- Magnesium deficiency and hypomagnesemia.
- Eclampsia. Empirical and clinical evidence supports the effectiveness of magnesium for this use. For this purpose, magnesium may act as a vasodilator, with actions in the peripheral vasculature or the cerebrovasculature, to decrease peripheral vascular resistance or relieve vasoconstriction. Additionally, magnesium may also protect the blood–brain barrier and thereby limit formation of cerebral edema, or it may act as a central anticonvulsant. The preparation usually used for this purpose is magnesium sulfate.
- Laxative use, particularly magnesium citrate and magnesium hydroxide
- Antiarrhythmic agent for torsades de pointes in cardiac arrest. Magnesium sulfate is the first-line agent for such use under the 2005 ECC guidelines and for managing quinidine-induced arrhythmias.
- As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma. Recent studies have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma. It is commonly administered via the intravenous route for the management of severe asthma attacks.
- Anti-contraction medication: Magnesium sulfate can also delay labor in the case of premature labor, to delay preterm birth.
More common side effects from magnesium include upset stomach and diarrhea, and calcium deficiency if calcium levels are already low.
Overdose of magnesium (hypermagnesemia) is only possible in special circumstances. It can cause nausea, vomiting, severely lowered blood pressure, confusion, slowed heart rate, respiratory paralysis. In very severe cases, it can cause coma, cardiac arrhythmia, cardiac arrest and death.
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