Sodium Carboxymethyl Starch – Pharmaceutical Excipient
Sodium carboxymethyl starch is a modified starch derivative widely used as a tablet disintegrant in pharmaceuticals, helping medicines dissolve quickly in the digestive tract.
Things worth knowing about "Sodium carboxymethyl starch"
Sodium carboxymethyl starch is a modified starch derivative widely used as a tablet disintegrant in pharmaceuticals, helping medicines dissolve quickly in the digestive tract.
What is Sodium Carboxymethyl Starch?
Sodium carboxymethyl starch, also known as sodium starch glycolate, is a chemically modified starch derivative primarily used as a tablet disintegrant in pharmaceutical manufacturing. It is the sodium salt of carboxymethyl starch, produced by chemically modifying natural starch – most commonly derived from potato or maize (corn) starch.
In the pharmaceutical and food industries, sodium carboxymethyl starch is one of the most widely used excipients. As a food additive in the European Union, it falls under the category of modified starches, regulated under E-numbers for starch modifications.
Production and Chemical Properties
Sodium carboxymethyl starch is produced by reacting starch with chloroacetic acid under alkaline conditions. This introduces carboxymethyl groups (-CH₂-COO⁻Na⁺) into the starch molecule. The resulting product is a white to off-white, odorless powder that swells significantly in water but does not dissolve completely.
- Chemical basis: modified potato or maize starch with carboxymethyl substituents
- Appearance: white to slightly yellowish powder
- Solubility: swells extensively in water, forming viscous gels
- pH stability: stable in mildly acidic to neutral conditions
Pharmaceutical Applications
The primary application of sodium carboxymethyl starch is in tablet manufacturing. As a disintegrant, it ensures that tablets break apart rapidly after ingestion, allowing the active ingredient to be released quickly. This significantly improves bioavailability – the proportion of the active substance that enters the bloodstream and produces an effect.
Mechanism of Action as a Disintegrant
Sodium carboxymethyl starch works through two main mechanisms:
- Swelling action: Upon contact with water or gastric fluid, the powder absorbs many times its own weight in liquid very rapidly, causing significant swelling. The internal swelling pressure breaks apart the tablet matrix.
- Capillary action: The material promotes the penetration of liquid into the tablet structure through capillary forces, further aiding disintegration.
The typical concentration used in tablet formulations is 2 to 8 percent of the total tablet weight.
Further Pharmaceutical Uses
- Filler in hard gelatin capsules
- Binder in granulation processes
- Excipient in topical formulations such as creams and gels
Food Industry Applications
As a food additive, sodium carboxymethyl starch functions as a thickening agent, stabilizer, and gelling agent. It is used in various processed foods to improve texture and consistency and to extend shelf life.
Safety and Tolerability
Sodium carboxymethyl starch is considered toxicologically safe and is recognized as safe by regulatory authorities including the European Food Safety Authority (EFSA) and the US Food and Drug Administration (FDA), which grants it GRAS (Generally Recognized As Safe) status.
- It is barely absorbed in the gastrointestinal tract and is predominantly excreted unchanged.
- Allergic reactions are very rare but possible in individuals with known starch hypersensitivity.
- The sodium content at typical pharmaceutical doses is low and clinically negligible, though it may be considered in patients on strict low-sodium diets.
Regulatory Status
In the European Union, sodium carboxymethyl starch is approved as a food additive. As a pharmaceutical excipient, it meets the requirements of the European Pharmacopoeia (Ph. Eur.) and the United States Pharmacopeia (USP).
References
- European Pharmacopoeia (Ph. Eur.) 10th Edition – Monograph: Sodium Starch Glycolate. European Directorate for the Quality of Medicines & HealthCare (EDQM), 2020.
- Rowe, R.C., Sheskey, P.J., Quinn, M.E. – Handbook of Pharmaceutical Excipients, 7th Edition. Pharmaceutical Press, London, 2012.
- European Food Safety Authority (EFSA) – Re-evaluation of modified starches as food additives. EFSA Journal, 2017;15(10):4986.
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