Magnesium - Effects and use
Magnesium is an enzymatic activator and an antagonist of calcium.
Magnesium forms complexes with ATP, ADP, orthophosphate, GTP… It is intercalated, by electrostatic bonds, between two oxygen atoms carrying each one a negative charge because of their ionization.
Interaction between ATP and the magnesium ion
Magnesium is necessary for the activity of the enzymes implicated in the transfer of phosphate groups: glucokinase, phosphofructokinase, phosphoglycerate-kinase, pyruvate-kinase, DNA-polymerase, ribonucleases, adenylcyclase, phosphodiesterases, guanylate-cyclase, like GTPases and ATPases of which Na+/K+-ATPase…
Antagonist of calcium
The effects of magnesium, deduced in particular from observations of deficiency and excess, are generally opposite to those of calcium.
Magnesium inhibits cation channels, sodium and especially calcium channels receptor and voltage-dependant and has a calcium antagonist effect. It protects mitochondrias against calcium overload.
- It inhibits the neuromuscular transmission by decreasing the release and effects of acetylcholine. It reinforces the effect of neuromuscular blocking agents. The decrease of magnesium, by facilitating neuromuscular transmission, can be at the origin of the symptoms of tetany and spasmophilia.
- It decreases neuronal excitability and is used in the treatment of certain seizures like those of eclampsia.
- It decreases cardiac conduction by slowing the slow diastolic depolarization.
- It inhibits platelet aggregation.
- It modulates the release of certain cytokines.
One can distinguish the therapeutic uses of magnesium according to its route of administration, parenteral or oral.
Magnesium is used by parenteral route:
- for the treatment of seizures associated with eclampsia.
- for the prevention of premature labour, because it inhibits uterine contractions. High doses, about 4 g , are given by intravenous infusion.
- for the prevention of arythmias, particularly torsades de pointes, in the acute phase of myocardial infarction.
- for the treatment of poisoning by cardiac glycosides for its calcium-antagonist effect.
The most frequent adverse effect of magnesium by parenteral administration is to induce a sinus bradycardia.
Magnesium is used by oral route to treat and prevent the deficiencies. The reality of a chronic magnesium deficiency is often difficult to demonstrate clinically and biologically because there is no simple and reliable biological marker.
A great number of studies suggest the beneficial role of a magnesium supplementation to reduce the progression of atherosclerosis, platelet aggregation or vascular spasms and arterial hypertension. These symptoms have multiple causes and magnesium is not a panacea but deserves to be regarded as a therapeutic adjunct. Since a supplementation by a moderated dose of magnesium, about 100 to 200 mg/day does not seem to have adverse effects and that it is not very expensive, its prescription in preventive or curative treatment of the disorders quoted previously seems justified.
Magnesium hydroxide and magnesium trisilicate are used as gastroduodenal antiacids and topics. They have a slight laxative effect and are often combined with preparations containing aluminum which have a constipant effect ( See “Aluminum”. ).