Oday Sajjad Alsawad^1,2 , Ahmed Abduljabbar¹

¹Department of Pharmaceutics, College of Pharmacy, University of Basrah, Basrah; ²Department of Pharmacy, Al-Manara College for Medical Sciences, Maysan, Iraq.

For correspondence:-  Oday Alsawad   Email: Oday.azeez@uobasrah.edu.iq

Received: 18 February 2026        Accepted: 20 May 2026        Published: 31 May 2026

Citation: Alsawad OS, Abduljabbar A. Evaluation of sustained-release metformin hydrochloride matrix tablets using blends of chitosan and xanthan. Trop J Pharm Res 2026; 25(5):607-617 doi: https://dx.doi.org/10.4314/tjpr.v25i5.2

© 2026 The authors.
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Abstract

Purpose: To develop sustained-release metformin matrix tablets using chitosan and xanthan, and to compare their performance with hydroxypropyl methylcellulose (HPMC; K100M) matrix and a commercial sustained-release (SR) product. Method: Metformin matrix tablet formulations were prepared by direct compression of chitosan-xanthan blends at ratios of 1:0 to 0:1, developed based on a 3x2-factorial design (polymer levels 25 – 35 % w/w). A formulation based on HPMC K100M (30 % w/w) and a commercial product were used as controls. Formulated tablets were tested for pre- and post-compression characteristics, swelling/erosion, in vitro dissolution, release kinetics and accelerated stability. Results: All blends showed fair to good flow (angle of repose 27.9 – 33.8°, Hausner ratio ≤ 1.24), friability (< 0.6 %) and content uniformity (98.1 – 101.3 %). Increasing polymer level and xanthan proportion slowed metformin release. Optimised 30 % chitosan: xanthan (1:1) matrix released 95.2 % metformin content after 12 h, closely matching HPMC formulation (96.0 %), and commercial SR product (f? = 67). The optimized product (F5) release fitted Higuchi/Korsmeyer-Peppas models (R² ≥ 0.99; n = 0.63), indicating anomalous diffusion. Stability testing showed no significant changes in all parameters tested (p > 0.05). Conclusion: Chitosan-xanthan matrices, especially the 1:1 mixture at 30 % w/w, produce stable metformin SR tablets with dissolution behaviour equal to those of HPMC and a commercially available SR metformin product, suggesting their use as alternatives to synthetic/semi-synthetic polymers in once-daily metformin dosage forms.

Keywords: Chitosan, Hydrophilic matrix, Metformin hydrochloride, Natural polymers, Sustained-release tablets, Xanthan gum

Impact Factor
Thompson Reuters (ISI): 0.6 (2023)
H-5 index (Google Scholar): 49 (2023)