Generic Premarin not approvable

FDA Consumer, July-August, 1997

Synthetic generic versions of the conjugated-estrogens drug Premarin will not be approved at this time, FDA has concluded. The generics are not shown to contain the same active ingredients as Premarin and, therefore, are not shown to work the same in treating menopausal symptoms and preventing osteoporosis.

Because generic drug makers do not have to repeat the clinical studies used to develop the brand-name drugs, they must ensure their products are as safe and effective by showing that the active ingredients are the same and that they are bioequivalent--that is, absorbed and used by the body in the same way as the original products.

Previously it was believed that two estrogens--sodium estrone sulfate and sodium equilin sulfate--were Premarin's sole active ingredients. New laboratory and clinical studies show this may not be the case. Other components in Premarin may contribute to its effectiveness. These and other findings, including a report by the agency's ad hoc working group on conjugated estrogens, underscore the lack of precise knowledge about Premarin.

FDA announced May 5 that Premarin must be better characterized before its active ingredients can be definitely identified and that the bioequivalence guidance for conjugated estrogens should be reexamined. The guidance describes how to measure whether the rate and extent of absorption in the blood of a generic version are equivalent to those of Premarin.

The agency encourages the start of studies that will permit scientific determination of the drug's active ingredients and provide a potential for approval of generic versions.

(For information about estrogen replacement therapy; see "New Attitudes Toward Menopause" in the March 1997 FDA Consumer.)

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