Transdermal Progesterone or Synthetic Progestogens

Abstract

The increasing use of transdermal progesterone creams and gels and the introduction of transdermal patches containing the progestogens norethisterone and levonorgestrel has led to a group of problems, concerns and enthusiastic claims for transdermal therapy regimens which require careful scrutiny and evaluation. From a review of the literature it appears that transdermal progesterone creams are poorly absorbed and, at the doses presently used for therapy regimens, do not achieve plasma levels sufficient to protect the endometrium from oestrogen-induced proliferation. On the other hand transdermal progestogen in the form of norethisterone is absorbed and achieves blood levels sufficient to inhibit mitosis or to induce a secretory change in the endometrium. Transdermal progestogens may not result in some of the adverse responses associated with oral therapy and therefore are likely to be the preferred route of delivery for those women who suffer from problems associated with oral preparations. Transdermal progestogen regimens achieve a constant low blood level rather than a high initial level followed by the rapid degradation, which is associated with oral progestogen therapy. This lower constant level may explain why transdermal progestogens may be associated with fewer adverse reactions than oral administration, and why the transdermal combined patches have a higher incidence of breakthrough bleeding.