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The aim of this study was to investigate the effects of solid dispersions (SD) and self-emulsifying (SE) formulations on the solubility and absorption properties of active components in total flavones of Hippophae rhamnoides L. (TFH). The solubility, dissolution rate, permeability and pharmacokinetics of isorhamnetin, quercetin and kaempferol in TFH SD/SE formulations and TFH were compared. The results showed that the solubility and dissolution rate of isorhamnetin, quercetin and kaempferol in SD/SE formulations were significantly enhanced compared to those in TFH, however, their intestinal permeability was comparable. The bioavailability of isorhamnetin, quercetin and kaempferol in rats remarkably increased after oral administration of TFH SD formulations compared to TFH, but there was no significant increase after oral administration of TFH SE formulations. The results of this study indicated the SD formulations on the improvement of pharmacokinetic properties of isorhamnetin, quercetin and kaempferol in TFH were much better than those of SE formulations. The improvement of pharmacokinetic properties of isorhamnetin, quercetin and kaempferol in TFH by SD formulations was probably ascribed to the enhancement of the solubility and dissolution of the three components, but was not relevant to the intestinal permeability. Therefore, as for herb extracts containing multiple components, especially for their major components with poor water solubility, solid dispersion formulations might have the better potential to enhance their bioavailability. [ABSTRACT FROM AUTHOR]

Myricetin is a natural flavonoid which has attracted great interest due to its antioxidant and free-radical scavenging activities. Unfortunately, physicochemical properties of myricetin are largely unknown so far and this would impair the design and development of myricetin formulations. In this paper, a series of studies were performed to investigate physicochemical properties of myricetin, such as its solubility in aqueous/organic solvents, aqueous solubility with different solubilizers, buffers and pHs, dissociation constant (pKa), partition coefficients of log P and log D at various pHs, intrinsic dissolution rate (IDR), and its stability at different temperatures and pHs. The results demonstrated that myricetin is a lipophilic compound with low water solubility but higher solubility in organic solvents or use of solubilizers. Myricetin is also a weak acidic compound with a pKa of 6.63 +/- 0.09, low IDR of 11.66 +/- 0.82 microg/min/cm2 at 37 degrees C. It is most stable at a pH of 2.0 and the degradation of myricetin is both temperature and pH dependent. Therefore, enhancement of the aqueous solubility and dissolution rate of myricetin and prevention from its rapid degradation at high pH and temperature should be considered for further formulation development of myricetin. In summary, these data will be used as rational support to create an efficacious formulation for the delivery of myricetin.