Norethisterone-cholesterol eutectic mixture as an oral sustained-release hormonal preparation: bioequivalence study in humans

In vitro release properties of etonogestrel and ethinyl estradiol from a contraceptive vaginal ring

The release properties of steroids from a combined contraceptive vaginal ring have been investigated. The product design is based on a coaxial fiber consisting of two types of polyethylene vinylacetate copolymers. Inside the core of the fiber, two steroids are present in a molecularly dissolved state. In order to design a controlled release system with specified release characteristics, values of diffusion coefficient and solubility are required. These data can either be determined during pre-formulation studies on e.g. polymeric flat films or from in-vitro release measurements of the actual coaxial fibers. It can be concluded from this study that polyethylene vinylacetate copolymers exhibit suitable properties to develop a controlled release system with the two steroids etonogestrel and ethinyl estradiol. It has been found that the permeability data obtained in the pre-formulation studies are useful in semi-quantitative terms, but deviate from the permeability data found from the in-vitro release of coaxial fibers. This is most likely due to differences in the polymeric structure of films and coaxial fibers. As a consequence, further studies should be initiated to evaluate the relationship between the manufacturing process and the resulting polymeric structure. It has also been found that the solubility and release of etonogestrel are influenced by the concentration of ethinyl estradiol. By investigating this phenomenon by thermoanalysis, it was shown that the steroids form an eutectic. The lower melting point of the steroids results in an increase in solubility and hence in altered permeability properties.

Absorption of oral ethinylestradiol is delayed by its eutectic mixture with cholesterol

A solid dispersion of ethinylestradiol-cholesterol (EE & CHOL; eutectic 1:4 W/W) was prepared by melting and rapid cooling. The fused material was then mixed with lactose as vehicle. Soft gelatin capsules were filled with 50 mg of the final mixture to give 0.050 mg of ethinylestradiol. Six female volunteers received, one capsule of the eutectic combination of EE:CHOL or one 50 micrograms tablet of ethinylestradiol (Dianor, Syntex), in a cross-over study and in fasting state. Venous blood samples were drawn at 0, 10, 20, 30, 40, 50, 60, 90, 120, 240, 360, 480, 720, 1440 minutes after dosing. Immunoreactive EE was measured by radioimmunoassay to assess the serum concentration-time course. All subjects exhibited a significant increase in EE levels after oral administration. Mean peak EE levels, 1350 pg/ml vs 91 pg/ml (p less than 0.001), were achieved 360 minutes and 90 minutes (p less than 0.01), after administration of the eutectic and reference formulation, respectively. Eutectic mixture showed a greater area under the serum concentration-time curve, longer mean residence time of the drug in the body, and four times the value of the elimination half-life of the reference formulation. It is concluded that the combination of ethinylestradiol with cholesterol forming an eutectic mixture, when administered orally to normal women, modulates the absorption and the bioavailability of the EE. This approach may be suitable for long-acting oral treatment with sex steroids.