Sodium bisulfite

• USP–NFSodium Bisulfite

Bisulfite of soda; sodium acid sulfite; sodium hydrogen sulfite; sulfurous acid monosodium salt; E222

Sodium hydrogen sulfite · [7631-90-5]

UNII TZX5469Z6I · PubChem CID 23665763

NaHSO3 · 104.06

Antioxidant, chelating agent

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

Sodium bisulfite is used as an antioxidant in acidic oral, parenteral and topical preparations, for example adrenaline and other sympathomimetic injections, at low concentrations comparable with those of sodium metabisulfite (typically 0.01–0.1% w/v). It also has antimicrobial activity at acidic pH and is used as a preservative and anti-browning agent in foods and beverages.

White or yellowish-white crystals or granular powder with an odour of sulfur dioxide. The solid article of commerce consists largely of sodium metabisulfite (Na2S2O5) together with some sodium bisulfite; in solution the two are equivalent.

Solubility

freely soluble in water; slightly soluble in ethanol

pH

aqueous solutions are acidic (about pH 4–5)

Sulfur dioxide content

pharmacopoeial material is assayed as SO2, with a minimum of about 58.5%

Effective pH range

best suited to acidic preparations; sulfite is preferred at neutral to alkaline pH

On exposure to air it slowly loses sulfur dioxide and is oxidised to sulfate. Aqueous solutions are oxidised by air, faster on heating and in the presence of metal ions. Store in a well-filled, airtight container protected from light, in a cool place.

Bisulfite reacts with sympathomimetic amines and other drugs bearing ortho- or para-hydroxybenzyl alcohol groups to form sulfonic acid derivatives with little or no activity, and adds to aldehydes and ketones. It inactivates thiamine and is incompatible with chloramphenicol, cisplatin, oxidising agents and strong acids (which release sulfur dioxide). It can also interact with rubber closures.

Made by passing sulfur dioxide into a solution of sodium carbonate or sodium hydroxide; on crystallisation the product separates mainly as sodium metabisulfite.

Sulfites can provoke bronchospasm, anaphylactoid reactions and other hypersensitivity reactions, especially in asthmatic patients, including after injection or inhalation. In the USA, products containing sulfites must carry a warning statement. JECFA has set a group ADI of 0–0.7 mg/kg body-weight, expressed as sulfur dioxide, for sulfites.

Observe normal precautions for the quantity handled. Sulfur dioxide may be released, particularly on contact with acids; use in a well-ventilated area with eye protection, gloves and, where necessary, respiratory protection.

GRAS listed, although sulfites may not be used in foods recognised as sources of thiamine or on fruit and vegetables intended to be eaten raw. Accepted as a food additive in Europe (E222). Included in the FDA Inactive Ingredient Database (injections, inhalation, ophthalmic, oral and topical preparations).

Potassium metabisulfite; sodium metabisulfite; sodium sulfite.

Choose the sulfite species by pH: bisulfite or metabisulfite for acidic preparations and sulfite for neutral or alkaline ones. Displacing headspace oxygen with nitrogen reduces the amount of antioxidant needed and slows its loss.