Percutaneous and transdermal oestrogen replacement therapy.

The benefits of oestrogen replacement therapy (ERT) have been widely recognized. However, among the drawbacks ascribed to ERT, metabolic disturbances have been observed, particularly after oral administration of oestrogens. Therefore, other routes of delivering oestrogens have been developed. The advantages of delivering drugs through the skin for systemic therapy have been widely recognized and represent a growing sector in drug development. Transdermal delivery of steroids is also a rapidly expanding field and in various clinical situations where hormonal replacement therapy is needed this route of administration is a real breakthrough, considering the relative toxicity of some steroids when given orally. Percutaneous application of steroids has been proven successful in various disorders. Various occlusive transdermal systems have also been designed, all of them aimed at achieving a constant release rate of the molecules contained in their reservoir through the intact skin. The skin itself, and especially the outermost layer, the stratum corneum, can play the role of a reservoir and a rate-controlling membrane. In the field of reproductive hormones, so far, oestradiol, progesterone and testosterone have been demonstrated to be good candidates for transdermal delivery. The effectiveness and the acceptability of transdermal delivery of oestradiol in postmenopausal women have been demonstrated. All the beneficial effects of oestrogen therapy can be achieved through skin delivery, e.g. symptoms relief as well as osteoporosis prevention.