Development and evaluation of dipyridamole sustained release tablets containing micro-environmental pH modifiers

The objective of the present study is to develop sustained release of dipyridamole, a poorly soluble weakly basic compound. The solubility of dipyridamole is the limit step of its bioavailability. To improve this, direct compressed tablets were formulated containing organic acids as pH modifiers to regulate micro-environmental pH on drug release from hydrophilic polymer matrix. Based on preliminary results from differential scanning calorimetry, fourier transform infrared spectroscopy, powder x-ray diffraction of dipyridamole with various polymer and pH modifier mixtures as well as tablet properties and drug release kinetics of dipyridamole tablets, HPMC K15 M and fumaric acid were selected as tablet matrix forming polymer and acidic micro-environmental pH modifier. Thereafter, tablets formulated with various concentrations of HPMC K15 M and fumaric acid were further evaluated. Among all the tablets fabricated, the tablet formulation containing 20% HPMC K15 M and 20% fumaric acid was observed to be the best formulation due to its near linear drug release profile in phosphate buffer medium (pH 6.8). Furthermore, under simulated gastrointestinal tract conditions, sustained drug release of approximately entire drug content from the tablets was achieved. This formulation has potential to improve dipyridamole bioavailability as well as therapeutic effect.