To the Editor.
—In the SPECIAL COMMUNICATION by Nightingale and Morrison1 concerning generic drugs, the subject of bioequivalence was discussed. However, no mention was made of bioavailability.In the past year, I have personally seen six patients who complained about the lack of effectiveness of oral estrogen therapy in alleviating their symptoms. Specific questioning revealed a difference between the control of their menopausal symptoms with the use of generic as opposed to brand name conjugated estrogens.In each instance, estradiol levels were below 37 pmol/L (10 pg/mL) or nondetectable. When these patients were switched to brand name conjugated estrogens, their menopausal symptoms were alleviated and their estradiol levels when rechecked were all above 165 pmol/L (45 pg/mL).The equine estrogens or synthetic estrogens are required by the United States Pharmacopeia to contain 50% to 63% estrone sodium sulfate, 22.5% to 32.5% equilin sodium sulfate, not more than 20% dihydroequilin,
Ansbacher R. Generic Drugs: Bioequivalence and Bioavailability. JAMA. 1988;259(2):220. doi:10.1001/jama.1988.03720020022028