Magnesium oxide

• BPHeavy Magnesium Oxide; Light Magnesium Oxide
• JPMagnesium Oxide
• Ph. Eur.Magnesium Oxide, Heavy; Magnesium Oxide, Light
• USP–NFMagnesium Oxide

Calcined magnesia; heavy magnesia; light magnesia; magnesia; magnesii oxidum; periclase; E530

Magnesium oxide · [1309-48-4]

MgO · 40.30

Diluent (filler), pH adjuster, buffering agent

Typical concentrations: — · Dosage forms: Solid

Used as an alkaline stabiliser or pH modifier in solid dosage forms of acid-labile drugs (for example in benzimidazole proton pump inhibitor formulations), as a diluent in tablets and capsules, and as an adsorbent and anticaking agent. It is used in foods and therapeutically as an antacid, laxative and magnesium supplement. As a stabiliser it is usually used at a few percent of the formulation.

A fine, white, odourless powder. The light form is very bulky; the heavy form is a denser powder.

Melting point

≈ 2800 °C

True density

≈ 3.6 g/cm³

Solubility

practically insoluble in water and ethanol; soluble in dilute acids

Aqueous suspension

strongly alkaline (pH about 10)

Absorbs moisture and carbon dioxide from the air, gradually converting to the hydroxide and basic carbonate; the light form does so more readily. Store in an airtight container in a cool, dry place.

Reacts with acids. Its alkalinity can degrade base-labile drugs, and it can adsorb or chelate drugs (for example tetracyclines, fluoroquinolones and some antimuscarinics), reducing their absorption. Incompatible with strong oxidising agents.

Produced by calcining magnesium carbonate or magnesium hydroxide; the calcination temperature largely decides whether the light (lower temperature) or heavy (higher temperature) form is obtained.

Regarded as non-toxic at excipient levels. Larger oral doses are laxative, and hypermagnesaemia may occur in patients with renal impairment. Inhalation of freshly generated fumes can cause metal fume fever.

Observe normal precautions for the quantity handled. Avoid generating dust; eye protection, gloves and a dust mask are recommended.

GRAS listed. Accepted as a food additive in Europe (E530). Included in the FDA Inactive Ingredient Database (oral capsules and tablets) and in non-parenteral medicines licensed in Europe.

Magnesium carbonate; magnesium hydroxide; calcium carbonate; sodium carbonate.

When used to stabilise acid-labile drugs, distribution of the alkaliser close to the drug (for example in the drug layer of coated pellets) is important. Its reactivity with water means granulation conditions and moisture content of the product should be controlled.