In a CMAJ letter to the editor on Premarin,1 Aldo Baumgartner states that "no other estrogen products have ever been developed that can match Premarin's unique composition of more that 10 estrogenic components." This is no doubt the case, as a large quantity of estrogenic metabolites are excreted via the urine of pregnant mares, not only of estradiol, but also of equilins, which are specific to horses. It is surprising that so many estrogenic components should be required to treat the post-menopausal lack of estrogen.
Baumgartner's offer to discuss Premarin provides the opportunity to pose the following questions: Are precise figures currently available on the number of steroid components in Premarin? To what extent has their spectrum of effects been elucidated? Has it been established that all of the metabolites produce only beneficial effects?
According to our estimates, Premarin must contain considerably more steroid metabolites than have been reported in the literature. A report recently appeared on the occurrence of hitherto unknown metabolites such as δ-8-estrone.2 It is particularly important in the case of long-term treatment with the preparation to know the effects of components that do not predominate quantitatively in the extract. We now know that estrogenic metabolites can produce a number of different effects;3 some metabolites are thought to increase the risk of breast cancer.4
Competing interests: None declared.
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