High-performance liquid chromatographic determination of 17β-estradiol and 17β-estradiol-3-acetate solubilities and diffusion coefficients in silicone elastomeric intravaginal rings

A rapid, sensitive reversed-phase high-performance liquid chromatographic method has been developed for the determination of in vitro release of 17β-estradiol and its ester prodrug, 17β-estradiol-3-acetate, from silicone intravaginal rings. Partial hydrolysis of the acetate under the aqueous conditions provided by the 1% benzalkonium chloride release medium necessitates its conversion to 17β-estradiol prior to HPLC analysis. Both steroid peaks have been fully resolved from the benzalkonium chloride peaks by the reported chromatographic method, which employs a C18 bonded reversed-phase column, an acetonitrile–water (50:50, v/v) mobile phase and a UV detection wavelength of 281 nm. The peak area versus 17β-estradiol concentration was found to be linear over the range of 0.0137–1347 μg ml−1. The HPLC method has also been used to determine the silicone solubilities and diffusion coefficients of the two related steroids. The almost 100-fold increase in 17β-estradiol-3-acetate release from the silicone core-type intravaginal rings compared to 17β-estradiol is shown to be due to a 60-fold increase in silicone solubility and a one and a half-fold increase in diffusitivity. The results demonstrate that an effective estrogen replacement therapy dose of 17β-estradiol may be administered from a silicone intravaginal reservoir device containing the labile 17β-estradiol-3-acetate prodrug.