Preparation and characterization of dipyridamole solid dispersions for stabilization of supersaturation: effect of precipitation inhibitors type and molecular weight.

Dipyridamole (DPL) is a weakly basic BCS class II drug which precipitates upon entering into intestine leading to pH dependant and variable absorption. Thus, research envisaged focuses on developing formulations that maintain supersaturation following upon acid to neutral pH transition. In an endeavor to accomplish the objective, solid dispersion (SD) with hydroxypropylmethyl cellulose (HPMC) and polyvinylpyrrolidone (PVP) was prepared by a quench cooling method. The three molecular weight grades of HPMC (HPMC E5, HPMC E15 and HPMC E50) and two molecular weight grades of PVP (PVP K30 and PVP K90) were investigated to observe effect of increasing molecular weight on stabilizing DPL supersaturated solutions. Equilibrium solubility studies revealed increase in solubility with both HPMC and PVP with greater benefit from HPMC. In vitro supersaturated dissolution results demonstrated that HPMC formulations provided greater degree and extent of supersaturation as compared to PVP formulations. The formulation with HPMC E50 provided maximum stabilization to supersaturation upon acid to neutral pH transition. Moreover, the effect of increase in molecular weight was more pronounced in HPMC rather than PVP. Stronger interactions were observed for DPL with HPMC, while no interaction was observed with PVP which was evident from Fourier transform infra-red studies. Differential scanning calorimetry and powder X-ray diffraction studies revealed the amorphous state of DPL in SD.