Magnesium oxide is an inorganic compound of magnesium, represented by the chemical formula MgO. Strongly hygroscopic, in the presence of water it transforms into the hydrated form, known as magnesium hydroxide Mg (OH) 2.
MgO + H2O = Mg (OH) 2
Under the name of magnesia, magnesium hydroxide is mainly known for its use as a laxative, just think of the famous S. Pellegrino magnesia, which contains 90% magnesium hydroxide. The dosage suggested by the manufacturer, in this case referring to adults, clarifies the health uses of this compound:
As an antacid 1 teaspoon (0.5-1.5g);
As a laxative 1 teaspoon (2-5 g);
As a purgative 1 tbsp.
The antacid effect of magnesium hydroxide emerges from the following chemical reaction, where HCl is the hydrochloric acid secreted by the parietal cells of the gastric mucosa
Mg (OH) 2 + 2HCl → MgCl2 + 2H2O
Not surprisingly, magnesium hydroxide is the active principle of MAALOX ®, a well-known antacid drug where it is combined with aluminum hydrate to neutralize its laxative effect and assist its antacid properties.
Side effects and contraindications: if taken in excess or for prolonged periods, magnesium oxide and / or magnesium hydroxide can cause kidney problems (linked to excessive intake of magnesium) and electrolyte imbalances. In the most serious cases it is possible the onset of dehydration or hypokalaemia, which can lead to cardiac or neuromuscular dysfunction, especially in the case of simultaneous treatment with cardiac glycosides, diuretics or corticosteroids.
For this reason, their use is contraindicated for patients suffering from kidney diseases and not recommended for the elderly, pregnant women and children.
In general, laxatives are contraindicated in subjects with acute abdominal pain or of unknown origin, nausea or vomiting, intestinal obstruction or stenosis, rectal bleeding of unknown origin, severe dehydration.
Laxatives can reduce the time spent in the intestine, therefore the absorption, of other drugs administered simultaneously orally.
Therefore, avoid taking laxatives and other drugs at the same time: after taking a medicine, leave an interval of at least 2 hours before taking the laxative.
Magnesium hydroxide, like all antacids, should not be taken at the same time as antibiotics of the tetracycline class as it reduces their absorption.
Milk or antacids can change the effect of the medicine; allow an interval of at least one hour to elapse before taking the laxative.
Association to avoid:
tetracyclines: formation of insoluble complexes with a reduction in the absorption and activity of these antibiotics.
Association not recommended:
quinidine: increased plasma rates of quinidine and risk of overdose due to decreased excretion.
Associations requiring precautions for use:
indomethacin, phosphorus, dexamethasone, digitalis, iron salts, nitrofurantoin, lincomycin: decreased absorption in the digestive system.
Magnesium Oxide as a Magnesium supplement
Of all the compounds used for specific additions to the mineral, magnesium oxide is the one containing the most generous percentages of magnesium, so much so that each gram of this compound contains 600 mg of the precious element. At the same time, magnesium oxide it is also the integrative form that raises the greatest criticisms, deriving from poor bioavailability; in other words, although it is particularly rich in magnesium, it contains it in a poorly absorbable form, consequently instead of being absorbed in the intestine and distributed to the tissues, the mineral is largely eliminated with the faeces.
The poor absorbability of magnesium oxide derives in part from the low solubility in water. Furthermore, in some studies conducted both in humans and in mouse models, this magnesium compound has shown a lower bioavailability compared to other forms of magnesium, evidenced by the poor increase in urinary concentrations after oral intake. The poor solubility in water seems an important parameter to evaluate the bioavailability of magnesium oxide: in some studies conducted on ruminant livestock, it was observed that the two aspects were proportional, which is why the dust finer magnesium oxide may be more bioavailable than coarser grains.
