798 Introduction Water-swellable polymer (hydrophilic colloid) matrices represent a simple and fexible approach to controlled drug delivery 1 . Combination of polymers in such matrices has been frequently applied to enable controlling drug release by adjusting the ratio of the combined polymers in the matrix former. Recently, there is an increased inter- est in using combinations containing ionizable polymers of pH-dependent swelling and erosion in CR matrix formulations. Such combinations are designed to mini- mize pH-dependent release, which is a common problem with peroral CR dosage forms that frequently causes in vivo variability and bioavailability problems and usually occurs with drugs exhibiting pH-dependent solubility and dis- solution rate in the pH range of the gastrointestinal tract 2 . Polymer combinations of xanthan gum with chitosan 3 and of HPMC with carrageenan 4 , sodium alginate (SA) 5 , and chitosan succinate 6 have been employed for this purpose. RESEARCH ARTICLE Evaluation of hydrophilic matrix tablets based on Carbopol ® 971P and low-viscosity sodium alginate for pH-independent controlled drug release Nizar M. Al-Zoubi 1 , Hatim S. AlKhatib 2 , and Wasfy M. Obeidat 3,4 1 Department of Pharmaceutical Sciences and Pharmaceutics, Applied Science University, Amman, Jordan, 2 Department of Pharmaceutics and Pharmaceutical Technology, University of Jordan, Amman, Jordan, 3 Department of Pharmaceutical Technology, Jordan University of Science and Technology, Irbid, Jordan, and 4 Current address: Faculty of Pharmacy Umm Al-Qura University, Makkah, Saudi Arabia Abstract Background: The aim of this study was to evaluate matrix tablets containing diferent ratios of Carbopol® 971P (CP) to low-viscosity sodium alginate (SA) and assess their suitability for pH-independent controlled drug release. Methods: Two processing methods (physical mixing, PM and spray-drying, SD) were applied before compaction and the release from corresponding matrices was compared. The release from CP-SA PM matrices was also investigated using three model drugs (paracetamol, salicylic acid, and verapamil HCl) and two dissolution media (0.1 N HCl or phosphate bufer, pH = 6.8), and the release rate, mechanism, and pH-dependence were characterized by ftting of Higuchi and Peppas models, and evaluation of similarity factor. Furthermore, swelling behavior of CP-SA matrix tablets was studied for evaluating its impact on drug release. Results: The processing method (SD or PM) markedly afected the drug release from CP-SA matrices. ANOVA tests showed signifcant efects of the CP:SA ratio and drug type on the release rate (expressed by the constant, K H , from Higuchi model) and of the dissolution medium on the release mechanism (expressed by the exponent, n, from Peppas model). Similarity factor (f 2 ) indicated that the CP:SA ratios ≥ 25:75 and ≥ 50:50 were suitable for pH-independent release of paracetamol and salicylic acid, respectively, although for verapamil HCl, the matrix with low CP:SA ratio (0:100) showed remarkably reduced pH-dependence of release. Swelling parameters (water uptake and mass loss) were signifcantly changed with experimental variables (CP:SA ratio, medium, and time) and were in good correlation with drug release. Conclusion: Matrix tablets based on CP and SA form a potentially useful versatile system for pH-independent controlled drug release. Keywords: pH-independent release, similarity factor, spray-drying, swelling, erosion Address for Correspondence: Nizar M. Al-Zoubi, Department of Pharmaceutical Sciences and Pharmaceutics, Faculty of Pharmacy, Applied Science University, Amman, Jordan 11931, E-mail: nizoubi@yahoo.com (Received 21 July 2010; revised 23 November 2010; accepted 30 November 2010) Drug Development and Industrial Pharmacy, 2011; 37(7): 798–808 © 2011 Informa Healthcare USA, Inc. ISSN 0363-9045 print/ISSN 1520-5762 online DOI: 10.3109/03639045.2010.545068 Drug Development and Industrial Pharmacy Downloaded from informahealthcare.com by 217.29.240.34 on 06/22/11 For personal use only.