Magnesium oxide is an inorganic magnesium salt, represented by the chemical formula MgO. Strongly hygroscopic, in the presence of water it is transformed into the hydrated form, known as magnesium hydroxide Mg (OH) 2 .
MgO + H 2 O = Mg (OH) 2Under the name of magnesia, magnesium hydroxide is known primarily for use as a laxative, just think of the famous S. pellegrino magnesia, which contains 90% magnesium hydroxide. The posology suggested by the producer, in this case referred to adults, clarifies the health uses of this salt:
As an antacid 1 teaspoon (0.5-1.5g);
As a laxative 1 teaspoon (2-5 g);
As a purgative 1 tablespoon.
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 → MgCl 2 + 2H 2 O
Not surprisingly, magnesium hydroxide is the active ingredient of MAALOX ®, a well-known antacid drug where it is combined with aluminum hydrate to neutralize its laxative effect and assist its antacid properties.
Undesirable effects and contraindications: if taken in excess or for prolonged periods, magnesium oxide and / or magnesium hydroxide can cause kidney problems (related to excessive magnesium intake) and electrolyte imbalances. In the most serious cases the onset of dehydration or hypokalaemia is possible, which can cause cardiac or neuromuscular dysfunctions, 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 state of dehydration.
Laxatives can reduce the time spent in the intestine, and therefore the absorption, of other drugs administered simultaneously orally.
Therefore avoid using 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 tetracycline antibiotics 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.
Avoid association:
tetracyclines: formation of insoluble complexes with reduction of the absorption and activity of these antibiotics.
Not recommended association:
quinidine: increase in plasma quinidine rates and risk of overdose due to decreased excretion.
Associations that need precautions for use:
indomethacin, phosphorus, dexamethasone, digitalis, iron salts, nitrofurantoin, lincomycin: decreased absorption at the level of the digestive system.
Magnesium oxide as a magnesium supplement
Of all the salts used for specific mineral additions, magnesium oxide is the one containing the most generous percentages of magnesium, so much so that every gram of this salt contains 600 mg of the precious element. At the same time, magnesium oxide is also the integrative form that raises the most 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 faeces.
The low absorbability of magnesium oxide derives in part from the low solubility in water. Moreover, in some studies conducted on both humans and murine models, this magnesium salt 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 cattle, it was observed that the two aspects were proportional, which is why the finest magnesium oxide powders could be more bioavailable compared to coarser ones.
