Improvement of solubility and oral bioavailability of rutin by complexation with 2-hydroxypropyl-β-cyclodextrin

The object of this study was to enhance the solubility, dissolution rate, and oral bioavailability of rutin by complexation with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD). The interaction of rutin with cyclodextrins (CyDs) was evaluated by the solubility, and ultraviolet (UV) and circular dichroism (CD) spectrophotometries. The chemical and enzymatic stability of rutin was examined in an alkaline buffer solution and in rat small intestinal homogenates, respectively. Dissolution rates of rutin and its CyD complexes were measured by the dispersed amount method. In vivo absorption studies of rutin after oral administration via conventional table containing rutin alone or its beta-CyD complexes was performed on beagle dogs. The stability constants calculated from the phase solubility method increased in the order of HP-gamma-CyD < G(2)-beta-CyD < beta-CyD < HP-beta-CyD. Spectroscopic studies also revealed that HP-beta-CyD and beta-CyD formed a relatively more stable inclusion complex with rutin. The dissolution rates of rutin increased by the complexation with CyDs in the order of rutin alone < HP-beta-CyD less than or equal to beta-CyD. HP-beta-CyD inhibited the hydrolysis of rutin in the alkaline buffer solution and the small intestinal homogenates of rats, suggesting that HP-beta-CyD may stabilize rutin in a gastrointestinal tract after oral administration. When the tablet containing rutin or its beta-CyD complexes was administered to beagle dogs, the plasma levels of homovanillic acid (HVA) (a major stable metabolite of rutin) after oral administration of HP-beta-CyD complex were much higher than in either that of rutin alone or in its beta-CyD complex. The in vitro absorption study suggests that HP-beta-CyD increased the oral bioavailability of rutin from the gastrointestinal tracts of beagle dogs because of the increase in solubility, faster dissolution rate, and gastrointestinal stability. HP-beta-CyD has a significant advantage with respect to providing high aqueous solubility while maintaining a lack of toxicity in oral pharmaceutical preparations of rutin.