To the Editor.
—The study by Dr Dong and colleagues1 confirms clinical experience that generic and brand-name levothyroxine preparations may be used for treating hypothyroidism. However, another important issue is whether substitution of 1 thyroxine preparation for another results in clinically significant changes in thyroid status. Based on a sophisticated statistical analysis that relies exclusively on comparing mean serum hormone levels, the authors conclude that the 4 thyroxine preparations tested "are interchangeable in the majority of patients."Given that serum thyrotropin levels provide the most accurate assessment of thyroid status, and that this parameter is used by virtually all clinicians to adjust thyroxine therapy, it is unfortunate that the authors did not provide the thyrotropin levels for individual patients in their study. These unpublished data have recently been released into the public domain,2 and they raise serious concerns about the conclusions and recommendations advanced by these investigators.Of the 24 thyroxine-treated
Germain DLS, Ridgway EC. Bioequivalence of Levothyroxine Preparations: Issues of Science, Publication, and Advertising. JAMA. 1997;278(11):895-896. doi:10.1001/jama.1997.03550110033018