To the Editor.
—The central question about the article by Dr Dong and colleagues1 is whether this study proves bioequivalence between preparations. I believe it is entirely inadequate for that purpose. The overriding problem is that not 1 of the 22 patients studied was proven to be athyrotic. Certainly the 15 patients with presumed Hashimoto thyroiditis, without documented hypothyroidism, had residual thyroid function. Probably the 7 patients with a thyrotropin level greater than 15 mU/L at some time also could provide significant endogenous hormone. Comparisons in this study represent the response to a mixture of endogenously and exogenously supplied hormone in unknown proportions. A valid comparison of thyroxine preparations can only be done in subjects who are without functional thyroid tissue.A second objection is to comparison of area under the curve (AUC) measurements, which, while logical for bioavailability of compounds that have rapid turnover, are useless for compounds
DeGroot LJ. Bioequivalence of Levothyroxine Preparations: Issues of Science, Publication, and Advertising. JAMA. 1997;278(11):895. doi:10.1001/jama.1997.03550110033017
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