Bioadhesive Matrix as Controlled Release Dosage Form for Verapamil Hydrochloride
Effect of mixing polymers on water uptake of the matrix and the drug release rate using simplex lattice design* )
Seham A. Elkheshen and Ehab A. Hosny
Department of Pharmaceutics, College of Pharmacy, King Saud University, Riyadh (Saudi Arabia)
Simplex lattice design with the aid of a computer software was utilized to study the effect of mixing hydrophilic polymers on the water uptake of a bioadhesive matrix and, consequently, on the rate and kinetics of release of verapamil hydrochloride. The applied design allows changing the quantity of different ingredients in the formulations in a systematic manner, yet keeping their total amount constant. The studied polymers were sodium carboxymethyl cellulose and hydroxypropylmethyl cellulose, representing the independent variables X1 and X2 in the design, respectively. Microcrystalline cellulose (AvicelÃ¢ PH101) is used as tablet filler as it aids in the direct compression of tablets. It was considered as the third variable (X3 ) in the design to be able to prepare matrices of constant weight, yet allowing the separation of Avicel effect on the measured responses, if any. The measured responses were the tabletsâ tensile strength, the water uptake of the matrix after 15 min and the rate of drug release. Avicel showed the highest effect on the tabletsâ tensile strength as well as on the rate of matrix water uptake. Hydroxypropylmethyl cellulose had the lowest rate of water uptake and, consequently, the most pronounced delaying effect on the release rate of the drug. An excellent correlation was observed between the rate of water uptake of different matrices and the rate of drug release. The correlation regression line had an R2 equal to 0.96.
Key words Bioadhesive matrix Â· Controlled release preparations Â· Hydrophilic polymers, water uptake Â· Simplex lattice design Â· Verapamil hydrochloride
* ) A preceding paper on the âEffect of the types and percen-tages of polymers on the release profile of the drugâ is published in Pharm. Ind. 60, No.6,p.555- 559 (1998).
Â© ECV- Editio Cantor Verlag (Germany) 1999
pharmind 1999, Nr. 7, Seite 666