Sodium sulfite

• BPAnhydrous Sodium Sulfite
• JPDried Sodium Sulfite
• Ph. Eur.Sodium Sulfite, Anhydrous
• Ph. Eur.Sodium Sulfite Heptahydrate
• USP–NFSodium Sulfite

Disodium sulfite; exsiccated sodium sulfite; natrii sulfis anhydricus; sulfurous acid disodium salt; E221

Disodium sulfite · [7757-83-7]

UNII VTK01UQK3G · PubChem CID 24437

Na2SO3 (anhydrous); Na2SO3·7H2O (heptahydrate) · 126.04 (anhydrous); 252.15 (heptahydrate)

Antioxidant, chelating agent

Typical concentrations: — · Dosage forms: Sterile (parenteral/ophthalmic)

Sodium sulfite is used as an antioxidant in neutral or alkaline oral, parenteral and topical preparations, at low concentrations of the same order as other sulfites (typically about 0.01–0.1% w/v). In acidic formulations sodium metabisulfite or bisulfite is used instead. It is also used as a preservative and antioxidant in foods.

The anhydrous form is a white, odourless powder; the heptahydrate occurs as colourless crystals, which effloresce in dry air and oxidise readily.

Solubility

freely soluble in water; very slightly soluble in ethanol

pH

aqueous solutions are alkaline (about pH 9–10)

Effective pH range

used at neutral to alkaline pH

Sodium sulfite is gradually oxidised to sodium sulfate by air, more rapidly in moist conditions and in solution; the heptahydrate is less stable than the anhydrous form. Store in a well-filled, airtight container in a cool, dry place.

Shares the incompatibilities of the other sulfites: it reacts with drugs containing ortho- or para-hydroxybenzyl alcohol groups, with aldehydes and ketones, and inactivates thiamine. Acids release sulfur dioxide, and it is incompatible with oxidising agents and heavy metal salts.

Made by reacting sulfur dioxide with sodium carbonate or sodium hydroxide solution in the appropriate proportion; the anhydrous salt is obtained by crystallisation above about 33 °C or by drying the heptahydrate.

Low systemic toxicity at antioxidant levels, but as with all sulfites, hypersensitivity reactions including bronchospasm and anaphylaxis can occur, particularly in asthmatic patients. JECFA has set a group ADI of 0–0.7 mg/kg body-weight, expressed as sulfur dioxide.

Observe normal precautions for the quantity handled. Eye protection and gloves are recommended.

GRAS listed, with the restrictions that apply to sulfites. Accepted as a food additive in Europe (E221). Included in the FDA Inactive Ingredient Database (injections, oral and topical preparations) and in medicines licensed in Europe.

Sodium bisulfite; sodium metabisulfite; potassium metabisulfite.

Specify whether the anhydrous form or the heptahydrate is used, as the heptahydrate contains about half its weight as water. Products containing any sulfite require the appropriate sulfite warning in the labelling of some markets.