[Non-oral administration of progesterone: experiences and possibilities of the transvaginal route]

Recent development of transdermal therapy permits application of estrogen, usually produced in the ovaries, in physiological dosage by means of continuous release from either an epidermal patch or dermal application of a gel. Transdermal therapy with progesterone, however is impossible due to poor dermal absorption and high dose requirements (release from corpora lutea: 25 mg/24 hours). Two other possibilities have been proposed. On one hand it is possible to apply norethisterone-acetate (NETA), another gestagen, epicutaneously. This mode of administration carries the same problems as oral application thus allowing for a dose reduction. On the other hand progesterone can be applied vaginally. This mode leads to significantly higher plasmatic concentrations of progesterone and has effects on the uterine mucosa similar to those in a normal cycle. This modality thus permits application of estradiol and progesterone in a physiological manner by a non oral route. It appears particularly interesting in patients at cardiovascular risk.