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February 22, 1980

Nonequality of Brand Name Thyroxine Preparations

Author Affiliations

USAF Wilford Hall USAF Medical Center Lackland AFB, Tex

JAMA. 1980;243(8):733. doi:10.1001/jama.1980.03300340013008

To the Editor.—  Despite widespread use of oral sodium levothyroxine preparations, there are few data available comparing efficacy of different brand name oral preparations. We studied ultimate bioavailability of thyroid hormone in two preparations, Letter and Synthroid 100-μg thyroxine tablets.Ten patients (three men and seven women) requiring treatment with thyroid hormone volunteered for the study. One had diffuse goiter, three had hypothyroidism, and six had thyroid nodules. Each was treated for one month with an appropriate dose of Letter (lot No. 7913416) dispensed as the 100-μg tablet and then for a second month with a numerically equivalent dose of Synthroid (lot No. ZD1678) dispensed as the 100-μg tablet. After each treatment interval, blood was drawn for determination of the serum thyroxine (T4) level (normal, 5.5 to 12.0 μg/dL),1 serum triiodothyronine (T3) level (normal, 84 to 220 ng/dL),2 triiodothyronine resin uptake (RT3U) (normal, 25%