Nasal Absorption Enhancement of 17β-Estradiol by Dimethyl-β-Cyclodextrin in Rabbits and Rats

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Abstract
A new formulation for nasal administration containing 17β-estradiol (E2) with dimethyl-β-cyclodextrin (DMβC) as a solubilizer and absorption enhancer is described. Nasal administration of this E2-DMβC formulation gave a significantly higher E2 absorption than an E2 suspension in both rabbits and rats. Relative to an intravenous injection of the E2-DMβC formulation, absolute bioavailabilities of 94.6 and 67.2% were calculated for the nasal E2-DMβC formulation in rabbits and rats, respectively. Differences in bioavailability may have resulted from differences in experimental animal conditions. The effects on human nasal ciliary activity of the E2-DMβC formulation were studied with an in vitro method. The formulation was found to exert only a minor effect on ciliary beat frequency. Thus, nasal delivery of E2, using a cyclodextrin inclusion formulation, may have potential for clinical application, e.g., in the therapy of postmenopausal disorders.