L-thyroxine dosage: a reevaluation of therapy with contemporary preparations.

Traditional L-thyroxine dosing formulas may overestimate the thyroid hormone requirement in patients treated with contemporary L-thyroxine preparations. We did clinical and laboratory assessments of 41 patients treated in successive periods with Levothroid (Armour Pharmaceuticals, Kankakee, Illinois) and Synthroid (Flint Division, Travenol Laboratories, Morton Grove, Illinois), obtaining 87 sets of data. Clinical subgroups were defined on the basis of the thyrotrophin response to thyrotrophin-releasing hormone. Normal responses were seen in 9 of 14 (64%) patients taking 100 micrograms/d and were associated with an average replacement dosage of 127 micrograms/d (1.7 micrograms/kg body weight). Nine of twenty-eight (32%) serum thyroxine values in the "physiologically replaced" group were elevated. Forty-three of fifty-four (80%) patients ingesting 125 micrograms or more had blunted responses (thyroxine "overreplaced"), averaging a daily dosage of 154 micrograms (2.14 micrograms/kg X d). No significant difference was found between Levothroid and Synthroid in predicting clinical group assignment. Guidelines for currently available L-thyroxine preparations should be revised and the recommended dosage reduced.

[1]  K. Burman,et al.  A rapid, sensitive enzyme-linked immunoassay for human thyrotropin. , 1985, Clinical chemistry.

[2]  J. Hennessey,et al.  The equivalency of two L-thyroxine preparations. , 1985, Annals of internal medicine.

[3]  F. B. Davis,et al.  Estimation of a physiologic replacement dose of levothyroxine in elderly patients with hypothyroidism. , 1984, Archives of internal medicine.

[4]  U. Barzel,et al.  Lean Body Mass is a Predictor of the Daily Requirement for Thyroid Hormone in Older Men and Women , 1984, Journal of the American Geriatrics Society.

[5]  I. Brajkovich,et al.  Serum T4, T3, and TSH levels in primary hypothyroidism during replacement therapy with thyroxine. , 1983, Metabolism: clinical and experimental.

[6]  M. Molitch,et al.  Aging and the thyroid. Decreased requirement for thyroid hormone in older hypothyroid patients. , 1983, The American journal of medicine.

[7]  T. Gimlette,et al.  Assessment of Optimal l-Thyroxine Replacement Dose by the TRH Test , 1982, Annals of clinical biochemistry.

[8]  U. Barzel,et al.  Levothyroxine replacement dose for primary hypothyroidism decreases with age. , 1982, Annals of internal medicine.

[9]  H. Maxon,et al.  A statistical method for determining normal ranges from laboratory data including values below the minimum detectable value. , 1979, Clinical chemistry.

[10]  N. Kuzuya,et al.  Changes in serum triiodothyronine, thyroxine, and thyrotropin during treatment with thyroxine in severe primary hypothyroidism. , 1976, The Journal of clinical endocrinology and metabolism.

[11]  R. Utiger,et al.  Serum thyroid hormone and thyrotropin concentrations during thyroxine and triiodothyronine therapy. , 1974, The Journal of clinical endocrinology and metabolism.

[12]  M. Surks,et al.  Replacement dosage of L-thyroxine in hypothyroidism. A re-evaluation. , 1974, The New England journal of medicine.

[13]  E. Young,et al.  Treatment of Hypothyroidism: A Reappraisal of Thyroxine Therapy , 1973, British medical journal.

[14]  C. Gorman,et al.  Suppression of thyrotropin (h-TSH) in serums of patients with myxedema of varying etiology treated with thyroid hormones. , 1971, The New England journal of medicine.