**5. Comparison of different vaginal progesterone preparations**

Natural progesterone have been incorporated in different forms for vaginal adminstration.e.g. vaginal tablets or capsules , vaginal pessaries and vaginal gel. The tablets adsorb the vaginal secretions and disintegrate into an adhesive powder that adheres to the vaginal epithelium, thus facilitating sustained absorption and reduced perineal irritation [44]. Each vaginal insert delivers 100 mg of progesterone in a base containing excipients conventionally used for solid oral dosage forms: lactose monohydrate, polyvinylpyrrolidone, adipic acid, sodium bicarbonate, sodium lauryl sulfate, magnesium stearate, pregelatinized starch, and colloidal silicone dioxide. Vaginal suppositories (e.g. Cyclogest)., contain semi-synthetic glycerides produced from interesterification of hydrogenated vegetable oil. The carrier vehicle in gel preparations (e.g. Crinone) is an oil-in-water emulsion containing polycarbophil, a bioadhesive and water-swellable polymer [28]. The water phase bypasses dependence on the local vaginal moisture, which is highly variable. The progesterone is sparingly soluble in oil (1:30 w/w) and practically insoluble in water (1:10,000 w/w) therefore the majority of the progesterone exists in a suspended form. The emulsion containing both dissolved and suspended progesterone adheres to the vaginal epithelial cells and thereafter-dissolved progesterone permeates through the mucosal tissue. The depletion of dissolved progesterone in the formulation is replenished by the dissolution of suspended progesterone particles
