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Rheological Properties of Xanthan Gum as a Thickening Agent in Oral Liquid Formulations
In the formulation of oral liquids, particularly syrups, suspensions, and pediatric solutions, achieving the ideal viscosity and flow behavior is critical for stability, ease of swallowing, and patient compliance. Xanthan gum, a high-molecular-weight polysaccharide produced through fermentation of Xanthomonas campestris, is widely used as a natural thickening and stabilizing agent. This blog explores its rheological characteristics and the reasons behind its growing use in pharmaceutical oral liquids.
1. Why Xanthan Gum?
Xanthan gum offers multiple benefits in pharmaceutical oral formulations:
Excellent shear-thinning behavior: Easier to swallow, especially for children or elderly patients
High viscosity at low concentrations: Effective thickening at 0.1–0.5% w/v
Stable over a wide pH range (4–10): Suitable for acidic or neutral oral solutions
Good compatibility with electrolytes: Useful for formulations containing salts
Suspension stability: Prevents sedimentation of active pharmaceutical ingredients (APIs)
2. Rheological Behavior: Pseudoplasticity
The most notable rheological feature of xanthan gum is its pseudoplastic (shear-thinning) nature. This means:
At low shear rates (e.g., when at rest), the viscosity is high, helping to maintain suspension stability.
At high shear rates (e.g., during pouring or swallowing), viscosity decreases, making the solution flow easily.
This non-Newtonian behavior ensures:
Better dose uniformity
Enhanced patient acceptability
Reduced clumping or sedimentation
3. Factors Affecting Xanthan Gum Viscosity
Several formulation parameters influence the rheological properties of xanthan gum:
| Factor | Effect |
|---|---|
| Concentration | Higher concentrations lead to exponentially increased viscosity |
| pH | Stable viscosity from pH 4 to 10; extreme pH may degrade polymer |
| Temperature | Stable up to 80°C; minor drop in viscosity at high temperatures |
| Ionic Strength | Compatible with most monovalent and divalent salts |
| Co-solvents (e.g., glycerin, sorbitol) | May slightly modify viscosity behavior |
Careful optimization is necessary to achieve the right balance between palatability and physical stability.
4. Applications in Oral Formulations
Xanthan gum is used in various oral dosage forms:
Pediatric syrups: Enhances mouthfeel, masks unpleasant taste, stabilizes suspension
Oral suspensions: Maintains API uniformity without hard sedimentation
Mucosal delivery systems: Improves adhesion and retention time in the oral cavity
It is also non-toxic, non-allergenic, and biodegradable, making it ideal for long-term formulations.
Conclusion
Xanthan gum is an effective and versatile thickening agent for oral liquids, offering superior rheological control, suspension stability, and patient-friendly textures. Its pseudoplasticity, stability over a wide pH and temperature range, and natural origin make it a preferred excipient in both OTC and prescription pharmaceutical liquids. Formulators should consider xanthan gum not only for its thickening capabilities but also for its role in enhancing formulation performance and patient compliance.
