Purpose: To evaluate the effect of two molecular weight grades of hydroxypropyl methylcellulose on the release characteristics of carvedilol phosphate matrix tablets.

Methods: Matrix tablets containing carvedilol phosphate were prepared from 27 formulations in three batch series coded A, B and C, each containing 9 formulations. Each batch incorporated different ratios of two molecular weight grades of hydroxypropyl methylcellulose (Methocel^® K4M CR and K15M CR) used as release retarding agents. Microcrystalline cellulose (Avicel PH 101), starch (Sta-Rx 1500) and lactose monohydrate were used as diluents in the formulations while the effect of sodium lauryl sulphate (wetting agent) was studied for some of the formulations. The tablets were characterized for carvedilol phosphate release in both simulated gastric and intestinal fluids. The data were subjected to different models in order to determine their release kinetics and mechanisms.

Results: All the batches released more than 50 % of their carvedilol content in 12 h when Methocel^® K4M CR and K15M CR constituted 18 % and 15 % of the matrix, respectively. Avicel^® PH 101 decreased while Starch 1500 and lactose monohydrate increased drug release. Drug release mechanism was predominantly diffusion.

Conclusion:  By using varying combinations of two molecular weight grades of hydroxypropyl methylcellulose as the matrix, controlled or sustained release carvedilol tablets of varying release characteristics can be prepared.