HRT: developments in therapy.
Various forms of oestrogen have been available for use as Hormone Replacement Therapy (HRT) for approximately 50 years. However, there has been little change in the mode of administration until the last 10-15 years. Although the oral route has remained the mainstay of therapy, non-oral routes of administration have been developed. During the 1970s it became clear that use of unopposed oestrogens in women with an intact uterus resulted in an increase in risk of endometrial carcinoma and thus the current practice of adding a sequential progestogen each month, to prevent endometrial hyperplasia, was introduced. However, certain progestogens can cause side-effects and some of the metabolic changes which they induce are potentially undesirable. Thus the search continues for new oral progestogens which are more 'metabolically friendly' than those in current use. Additionally, non-oral delivery systems for progestogens have been studied, such as the transdermal route (patches) and local administration within the uterine cavity (progestogen-containing intra-uterine devices). Both these strategies may minimise their symptomatic, psychological and metabolic effects. Continuous (every day) administration of progestogens in combination with the oestrogen, or the use of new compounds (e.g. tibolone) may overcome the problem of regular withdrawal bleeding which some women find unacceptable. However, it remains to be determined whether such therapies are as efficacious as conventional oestrogen/sequential progesterone regimens.