The Effect of Water Soluble Polymers on Felodipine Aqueous Solubility and Complexing Abilities with Natural and Modified β-Cyclodextrin

       Purpose of this study was to investigate the effect of the presence of the water soluble polymers viz HPMC, PVP and PEG 6000 on aqueous solubility and complexation abilities of felodipine with or without presence of β-cyclodextrin (βCD) and HPβCD by phase solubility studies. The data revealed the initial increase in drug solubility followed by plateau in the presence of relatively low polymer concentration i.e. 0.25-0.5 %w/v. Phase solubility diagrams of felodipine in ternary system showed similar behaviour to binary system without βCD. Addition of water soluble polymer to βCD solution improved βCD solubilizing efficiency due to increase in βCD complexing power toward felodipine. In binary system solubility was found 2.5 to about 10 times higher than in water which was further improved in the   presence of 0.25% w/v water soluble polymer. Ternary systems with βCD showed highest increments in solubility towards felodipine, with 78.8%, 81.8% and 74% improvement after the addition of 0.25% w/v HPMC, PVP and PEG6000, respectively. Our study confirmed that addition of small amounts of hydrophilic polymer is useful strategy for improving the solublization and complexing abilities of cyclodextrins thus allowing less cyclodextrin to be needed to solubilize given amount of drug. This offers economic advantage. All the polymers under study showed synergistic effect on felodipine cyclodextrin solublization by increasing complexation efficiency.The highest solubility improvement up to 81.8% was obtained for βCD ternary system when 0.25% w/v of PVP was used.