Sodium metabisulfite

• BPSodium Metabisulfite
• JPSodium Pyrosulfite
• Ph. Eur.Sodium Metabisulfite
• USP–NFSodium Metabisulfite

Disodium disulfite; disodium pyrosulfite; natrii metabisulfis; sodium disulfite; sodium pyrosulfite; E223

Disodium disulfite · [7681-57-4]

UNII 4VON5FNS3C · PubChem CID 656671

Na2S2O5 · 190.11

Antioxidant, chelating agent

Typical concentrations: 0.01–1% · Dosage forms: Liquid, Sterile (parenteral/ophthalmic)

Sodium metabisulfite is used as an antioxidant in oral, parenteral and topical preparations at concentrations of about 0.01–1.0% w/v, most often around 0.1%. It is used mainly in acidic preparations (for example adrenaline, local anaesthetic with vasoconstrictor, and some aminoglycoside injections), while sodium sulfite is preferred at higher pH. It also has antimicrobial activity in acidic conditions and is used as a preservative in foods and beverages.

Colourless, prismatic crystals or a white to creamy-white crystalline powder with an odour of sulfur dioxide and an acidic, saline taste. In aqueous solution it forms sodium bisulfite.

pH

3.5–5.0 (5% w/v aqueous solution)

Solubility

freely soluble in water (about 1 in 2); slightly soluble in ethanol; freely soluble in glycerol

Thermal behaviour

decomposes above about 150 °C, releasing sulfur dioxide

Sulfur dioxide content

theoretical about 67% w/w; pharmacopoeial assay is expressed as Na2S2O5

On exposure to air and moisture it is slowly oxidised to sodium sulfate, with loss of sulfur dioxide and disintegration of the crystals. Aqueous solutions also oxidise in air, especially on heating, and are best prepared with water purged of oxygen and filled under nitrogen. Store in a well-filled, airtight container protected from light, in a cool, dry place.

Reacts with sympathomimetics and other drugs that are ortho- or para-hydroxybenzyl alcohol derivatives to form inactive sulfonic acid derivatives. Incompatible with chloramphenicol (in some cases), cisplatin and thiamine, which it inactivates, and with phenylmercuric acetate in eye drops. Strong acids liberate sulfur dioxide. It can also react with rubber closures, which should be pre-treated.

Prepared by saturating a solution of sodium hydroxide or sodium carbonate with sulfur dioxide and crystallising the product, which separates as the metabisulfite.

Sulfites are oxidised to sulfate in the body and are of low systemic toxicity at the levels used, but they can cause severe hypersensitivity reactions, including bronchospasm and anaphylaxis, particularly in asthmatic patients, after oral, parenteral or inhaled exposure. A sulfite warning is required on US prescription drug labelling. JECFA has set a group ADI of 0–0.7 mg/kg body-weight, expressed as sulfur dioxide.

May release sulfur dioxide, which irritates the eyes and respiratory tract; handle in a well-ventilated area, avoid contact with acids, and wear eye protection, gloves and, where dust or gas is generated, respiratory protection.

GRAS listed, with restrictions (not to be used in foods that are recognised sources of thiamine). Accepted as a food additive in Europe (E223). Included in the FDA Inactive Ingredient Database (IM, IV and other injections, inhalation, ophthalmic, oral, otic, rectal and topical preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Potassium metabisulfite; sodium bisulfite; sodium sulfite; sodium thiosulfate.

Because it is consumed as it protects the drug, the residual sulfite content should be monitored on stability, and the minimum effective level used. In multidose preparations, sulfite-preservative combinations should be checked, since sulfites can inactivate some preservatives.