Formulation and Optimization of Gastric Bioadhesive Tablets of Diltiazem Hydrochloride using Central Composite Design

Purpose: To develop bioadhesive tablets of diltiazem hydrochloride with a unique combination of bioadhesion and drug release.
Method: Tablets were prepared by physical blending of diltiazem hydrochloride with two polymers, viz., carbopol and hydroxylpropyl methyl cellulose in different ratio along with other excipients. A 3² central composite design was employed to optimize the formulations on the basis of phycochemical properties, bioadhesive strength (measured as force of detachment from gastric mucosa) and in vitro drug release. HPMC K 4M and Carbopol 934P were taken as the independent variables. Contour plots were drawn and optimum formulations were selected by feasibility and grid searches.
Results: The tablets showed excellent bioadhesive strength which varied from 7.6 to 21 g. Both polymers had effect on the bioadhesive strength of the tablets and maximum bioadhesion was observed at the highest level of both the polymers. The drug release from the formulation varied from 79.74 to 94.54 % in 12 h. The diffusion exponent (n) of Korsmeyer-Peppas model ranged from 0.491 to 0.658 which indicates the mechanism of drug release was anomalous transport; the diffusion exponent (n) increased with increase in the amount of either polymer in the bioadhesive tablet.
Conclusion: Floating bioadhesive tablets of diltiazem hydrochloride with good bioadhesion and controlled release characteristics is feasible.

Keywords
Drug delivery; Gastroretentive; Bioadhesive; Diltiazem; Central composite design