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Serum triiodothyronine concentrations change less after sustained-release triiodothyronine than standard triiodothyronine
The background of the study. Administration
of triiodothyronine (T3) results in transient, nonphysiologic rises
in serum T3 concentrations, which is one reason why T3 is not often
given therapeutically. In this study the effects of sustained-release
and standard preparations of T3 were compared in patients with hypothyroidism.
How the study was done. The study subjects were 15 patients with hypothyroidism who had been treated with T4 for at least three months. The patients were given their usual dose of T4 for six weeks. They then took T4 plus 6 µg of standard T3 or T4 plus 6 µg of sustained-release T3 daily, each for six weeks, in a random crossover protocol. At the end of each period, serum total T4 and total T3 were measured before and 1.5, 3, 6, and 9 hours after ingestion of T4 or T4 plus T3.
The results of the study. Serum T4 concentrations increased by approximately 20 percent 1.5 to 3 hours after T4 ingestion at the end of all three six-week study periods. In contrast, serum T3 concentrations varied; there was no change at the end of the T4 period, a small, sustained rise at the end of the T4-plus-sustained-release-T3 period, and an early rise and a fall at the end of the T4-plus-standard-T3 period. The mean peak serum T3 concentration was 119 ng/dl (1.8 nmol/L) in the T4-plus-standard-T3 group and 108 ng/dl (1.7 nmol/L) in the T4-plus-sustained-release-T3 group; the respective peak serum T3 values were at 3.2 and 5.0 hours.
The conclusions of the study. A sustained-release preparation of T3 results in less variation in serum T3 concentrations than ingestion of standard T3.
The original article. Hennemann
G, Docter R, Visser TJ, Postema PT, Krenning EP. Thyroxine plus
low-dose, slow-release triiodothyronine replacement in hypothyroidism:
proof of principle. Thyroid 2004;14:271-5.
Next Article: Thyroxine therapy has little effect on thyroid
nodules in postmenopausal women
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