Sodium Metabisulfite Excipient | Uses, Suppliers, and Specifications
Sodium Metabisulfite is an inorganic compound and the sodium salt of sulfuric acid (chemical formula Na2S2O5). Its IUPAC name is Sodium pyrosulfite and is also known as Sodium disulfite. Sodium Metabisulphite is an approved pharmaceutical excipient and is supplied as a white or yellowish-white powder.
Synonyms and Trade Names: Sodium Metabisulphite; Sodium Pyrosulfite; Sodium Disulfite; Disulfurous Acid, Disodium Salt; Sodium Acid Sulfite; E223S
Uses and Applications: Diluent; Alkalizing Agent; Antimicrobial Agent; and Antioxidant
Sodium metabisulfite (or Sodium pyrosulphite) is an inorganic sulphur compound with the chemical formula Na2S2O5. It is sometimes referred to as disodium metabisulfite. It occurs as colourless, prismatic crystals or as a white to creamy-white crystalline powder that has the odour of sulfur dioxide and an acidic, saline taste.
Sulfites such as Sodium metabisulfite, are naturally occurring mineral substances with a long history of use in food products. They naturally occur in some foods and are widely added as a food additive to prevent microbial spoilage and preserve colour. Dried fruits, sausages, cordials and wines are examples of food products containing sulfites.
Sulfites have been widely scrutinised over the years. Many scientific committees have thoroughly investigated their safety and concluded that for most people sulfites are safe. However, some sulfite-sensitive individuals, such as those who have asthma, may react to sulfites with allergy-like symptoms.
Commercial grades of Sodium metabisulfite are prepared by saturating a solution of sodium hydroxide with sulfur dioxide and allowing crystallization to occur; hydrogen is passed through the solution to exclude air. Sodium metabisulfite may also be prepared by saturating a solution of sodium carbonate with sulfur dioxide and allowing crystallization to occur, or by thermally dehydrating sodium bisulfite. The material crystallizes from cold water as a hydrate containing seven water molecules.
Sodium metabisulfite is known to contain small amounts of Sodium sulfite and Sodium sulfate.
Chemical Structure & Identifiers
|CAS Registry Number||[7681-57-4]|
|Molecular Weight||190.1 g/mol|
|UNII Code (FDA)||4VON5FNS3C|
Sodium metabisulfite is an approved pharmaceutical excipient. It is currently listed in all the major pharmacopoeia and included in the FDA Inactive Ingredients Database (covering injections; ophthalmic solutions; oral preparations; and topical products). A specification for sodium metabisulfite is contained in the Food Chemicals Codex (FCC). It is also GRAS listed and accepted for use as a food additive in Europe.
|Appearance||White to creamy-white crystalline powder|
|pH||pH = 3.5—5.0 (5% w/v aqueous solution at 20 oC)|
|True density||1.480 g/ml|
|Melting point||Melts with decomposition at less than 150 oC|
|Osmolarity||a 1.38% w/v aqueous solution is iso-osmotic with plasma|
|Solubility||Soluble in water, ethanol (95%) and glycerine|
|Official name||Sodium Metabisulfite||Sodium Metabisulphite||Sodium Pyrosulfite|
|Appearance of solution||n/a||specified||specified|
|pH (5% w/v solution)||n/a||3.5 -5.0||n/a|
|Arsenic||n/a||≤ 5 ppm||≤ 4 ppm|
|Heavy metals||≥ 0.002%||≤ 20 ppm||≥ 20 ppm|
|Iron||≤ 0.002%||≤ 20 ppm||≤ 20 ppm|
|Assay (as Na2S2O5)||n/a||≥ 95.0 -100.5%||≥ 95.0%|
|Assay (as SO2)||65.0 -67.4%||n/a||n/a|
Key: n/a Specification is not listed
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Applications in Pharmaceutical Formulations or Technology
The main use of Sodium metabisulfite in pharmaceutical products is an antioxidant in oral, parenteral, and topical pharmaceutical formulations. Typical concentrations are 0.01-1.0% w/v. It is mainly used in acidic formulations (while Sodium sulfite is used for alkaline preparations).
Sodium metabisulfite also possesses antimicrobial activity, which is known to be highest at acidic pH. For this reason, it can be used as a preservative in suitable oral preparations (e.g syrups).
As mentioned above, Sodium metabisulfite is used in the food industry (and in wine production) both as an antioxidant and antimicrobial preservative. It is also used to prevent oxidative browning of food products.
Safety and Precautions
Sodium metabisulfite is widely used in oral, topical, and parenteral pharmaceutical products as an antioxidant. Additionally, Sodium metabisulfite is also used in various food products where it functions as an antimicrobial preservative. However, despite being widely used in many products, Sodium metabisulfite and other sulfites have been linked with adverse reactions, including hypersensitivity-type reactions and anaphylaxis. Some individuals with asthma are known to be sensitive to allergic reactions to sulfite antioxidants.
Upon oral intake, Sodium metabisulfite is oxidized to sulfate and is excreted in the urine. Ingestion of large amounts of Sodium metabisulfite can gastric and circulatory system disturbances, CNS depression, and even death. In the European Union, the acceptable daily intake of Sodium metabisulfite and other sulfites used in foodstuffs is set at up to 3.5 mg/kg body-weight (calculated as sulfur dioxide). The WHO has set an acceptable daily intake of Sodium metabisulfite, and other sulfites, at up to 7.0 mg/kg body-weight, calculated as sulfur dioxide.
Food Standards regulations on added sulfites mandate that a declaration on the label of a packaged product is made when present in foods in concentrations of 10 mg/kg or more. This is to safeguard consumers who may be sensitive to sulfites to avoid them.
Toxicology: LD50 (rat, IV): 0.12 g/kg.
Stability and Storage Conditions
Sodium metabisulfite is generally a stable material if stored correctly. The assigned shelf life s 24-36 months. The bulk material should be stored in a well-closed container, protected from light, in a cool, dry place. When exposed to air and moisture, Sodium metabisulfite is slowly oxidized to Sodium sulfate with disintegration of the crystals. The presence of strong mineral acids in the solid decomposes the material and liberates sulfur dioxide.
Aqueous Sodium metabisulfite solutions can also decompose in air, particularly when heated. Therefore, solutions meant for autoclaving should be filled into containers in which the air has been replaced with nitrogen gas to create an inert atmosphere. Dextrose decreases the stability of Sodium metabisulfite.
When handling Sodium metabisulfite, workers should observe applicable SHEQ protocols appropriate to the circumstances and quantity of material handled. Sodium metabisulfite is a potential irritant to the skin and eyes. therefore, PPE (eye protection and gloves) is recommended. In the UK, the long-term (8 hour TWA) workplace exposure limit for Sodium metasulfite is 5mg/m3.
Sustainability and Environmental Impact
A sustainability assessment for Sodium metabisulfite has not been undertaken.
Manufacturers & Suppliers
- Sodium Metabisulfite
Additional Resources (Downloads)
References and Literature Used
. van Heugten AJP, de Vries WS, Markesteijn MMA, Pieters RJ, Vromans H. The Role of Excipients in the Stability of Triamcinolone Acetonide in Ointments. AAPS PharmSciTech. 2018 Apr;19(3):1448-1453. doi: 10.1208/s12249-018-0957-8. Epub 2018 Feb 15. PMID: 29450828.
. García-Gavín J, Parente J, Goossens A. Allergic contact dermatitis caused by sodium metabisulfite: a challenging allergen: a case series and literature review. Contact Dermatitis. 2012 Nov;67(5):260-9. doi: 10.1111/j.1600-0536.2012.02135.x. Epub 2012 Aug 1. PMID: 23039002.
. Shojaee S, Nokhodchi A, Cumming I. The role of fillers and sodium metabisulfite on drug release from aged polyox tablets. Drug Dev Ind Pharm. 2014 Nov;40(11):1451-8. doi: 10.3109/03639045.2013.828224. Epub 2013 Aug 20. PMID: 23962147.
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