277 KEY WORDS: Verapamil HCl, Synthetic polymers, Sustained release, Tablet evaluation techniques, Mathemati- cal kinetics models. * Author to whom correspondence should be addressed. E-mail: ahmadkingsk@yahoo.com Latin American Journal of Pharmacy (formerly Acta Farmacéutica Bonaerense) Lat. Am. J. Pharm. 34 (2): 277-82 (2015) Regular article Received: September 19, 2014 Revised version: December 13, 2014 Accepted: December 14, 2014 Formulation Development and In Vitro Characterization of Sustained Release Matrix Tablets of Verapamil HCl Using Synthetic and Natural Polymers Ahmad KHAN * 1 , Muhammad IQBAL CH 2 , Jallat KHAN 3 , Gul MAJID KHAN 1 , Muhammad HANIF 4 & Amjad KHAN 5 1 Department of Pharmacy, Quid I Azam University Islamabad, Pakistan 2 Department of Pharmacy, University of Faisalabad, Pakistan 3 Department of Chemistry, Islamia University Bahawalpur, Pakistan 4 Faculty of Pharmacy, Bahauddin Zakariya University Multan, Pakistan 5 Department of Biotechnology, Quaid I Azam University Islamabad, Pakistan. SUMMARY. The pharmaceutical attributes of sustained release (SR) oral tablets containing verapamil hy- drochloride prepared by using synthetic polymers (HPMC K4M and Na carboxymethylcellulose) and nat- ural hydrophilic matrix formers (xanthan gum and Acacia) were observed in the present work. Direct compression method was used for the preparation of sustained release matrix tablet using the polymers in different ratios. Compressed tablets were evaluated for hardness, friability, weight variation and in vitro dissolution using USP dissolution apparatus-II. Dissolution profiles of test formulations were obtained in 900 mL distilled water for 12 h at 37 °C. The data was then kinetically evaluated with different mathemat- ical models i.e., Zero Order, First Order, Higuchi, Hixson-Crowell, Baker & Lonsdale, Korsmeyer and Peppas, Weibull, Hoffenberg and Peppas Sahi. Different verapamil hydrochloride matrix tablet formula- tions have shown different dissolution behavior and it was concluded that the synthetic polymers HPMC K4M and Na carboxymethylcellulose in combination is a better choice for sustained release formulation development for verapamil hydrochloride. Furthermore, the results of similarity factor f 2 between the compressed formulations and Calan SR® have verified formulation F4 (having synthetic polymers) as op- timized formulation due to greatest similarity. RESUMEN. Se estudiaron los atributos de liberación sostenida (SR) de tabletas orales que contienen clorhidrato de verapamilo preparado usando polímeros sintéticos (HPMC K4M y Na carboximetilcelulosa) y formadores de matriz hidrófilos naturales (goma xantan y goma de Acacia). El método de compresión directa se utilizó para la preparación de tabletas de liberación sostenida usando los polímeros en diferentes proporciones. Las tabletas comprimidas se evaluaron para dureza, friabilidad, variación de peso y disolución in vitro usando para la disolu- ción el aparato II USP. Los perfiles de disolución de las formulaciones de ensayo se obtuvieron en 900 mL de agua destilada durante 12 h a 37 °C. Los datos fueron entonces cinéticamente evaluados con diferentes modelos matemáticos es decir, de orden cero, de primer orden, Higuchi, Hixson-Crowell, Baker & Lonsdale, Korsmeyer y Peppas, Weibull, Hoffenberg y Peppas Sahi. Las diferentes formulaciones de comprimidos de clorhidrato de ve- rapamilo mostraron diferente comportamiento de disolución y se concluyó que los polímeros sintéticos HPMC K4M y Na Carboximetilcelulosa en combinación es una mejor opción para el desarrollo de formulaciones de li- beración sostenida. Además, los resultados del factor de similitud f 2 entre las formulaciones y Calan SR® han verificado que la formulación F4 (con polímeros sintéticos) es la óptima debido a su mayor similitud. INTRODUCTION Pharmaceutical manufacturers have been striving enough for about quarter a century in- troducing a great many products, described as having properties of “sustained release,” “pro- longed action,” or “repeat action”, which, after their administration, are claimed to provide a long-term therapeutic response 1 . For the last three decades oral sustained release dosage forms have been developed for the reason that they have sufficient therapeutic advantage 2 . Verapamil, calcium channel antagonist, is frequently recommended in the management of essential hypertension are available in the range of 40-240 mg strengths. Its solubility is pH de- pendent, having high solubility in gastric pH which decreases in the intestinal pH. It is usual- ly used in a tablet form usually containing 40 ISSN 0326 2383 (printed ed.) ISSN 2362-3853 (on line ed.)