This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Peran, S. Articles by Peran, M. Search for Related Content PubMed PubMed Citation Articles by Peran, S. Articles by Peran, M.

Increase in Plasma Thyrotropin Levels in Hypothyroid Patients during Treatment due to a Defect in the Commercial Preparation

Laboratorio de Endocrinología Molecular, Hospital Regional de Málaga; Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Málaga (M.P.); and Unidad de Endocrinología Molecular, Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas Facultad de Medicina, Universidad Autónoma de Madrid (G.M.d.E., M.A.), Madrid, Spain

Address all correspondence and requests for reprints to: Dr. Salvador Peran, Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Campus de Teatinos, Universidad de Málaga, 29071 Málaga, Spain. E-mail: peran{at}uma.es

Around mid-1995, the Molecular Endocrinology Laboratory of the Regional Hospital (Malaga, Spain) began detecting an increase in TSH levels in the serum of patients under study to control the treatment of hypothyroidism with levothyroxine. Over a period of 5 months, of a total of 467 hypothyroid patients treated with Levothroid, 53% had TSH levels higher than 6 µU/mL. The reliability of the biochemical results was verified by duplicating 56 randomly chosen samples from all those with high TSH levels and by an external control performed in four different laboratories. The amount of levothyroxine in the tablets was analyzed by RIA, high performance liquid chromatography, and their iodine contents. The lowest levels of levothyroxine found in the 50-µg Levothroid tablets were those determined by RIA, with a mean value of 32.3 µg, resulting in a 35.3% loss of activity. The mean value of levothyroxine found in these same tablets by high performance liquid chromatography was 39.3 µg, amounting to a 21.3% loss in activity. The iodine showed no significant loss in these tablets, with a mean experimental value of 48 µg. The commercial laboratory withdrew lot J from the market, the one in which these deficiencies were found.