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Combined thyroxine and triiodothyronine therapy is not more effective than thyroxine alone in patients with hypothyroidism (III)
The background of the study. This large study,
like the two preceding studies, compared the effects of thyroxine
(T4) alone and T4 plus triiodothyronine (T3) in patients with hypothyroidism.
How the study was done. The study subjects were 697 patients with hypothyroidism recruited from 28 family practices in the United Kingdom. All had taken 100 µg or more of T4 daily for at least three months and had normal serum thyrotropin (TSH) concentrations.
The patients were randomly assigned to take their usual dose of T4 or that dose of T4 less 50 µg plus 10 µg of T3 daily (T4:T3 ratio 5:1 to 15:1). They were studied at base line and after 3 and 12 months. The evaluations included questionnaires about general health, symptoms of hypothyroidism, anxiety, depression, mood, and cognitive function. The primary end point was the score on the general health questionnaire at three months. Serum TSH, free T4, free T3, and thyroid-related substances were also measured.
The results of the study. At 3 and 12 months, 616 patients (88 percent) and 573 patients (82 percent), respectively, were taking their assigned therapy. At three months, the score on the general health questionnaire improved in both groups, with slightly greater improvement in the T4-plus-T3 group. The hypothyroid-symptom, anxiety, and depression scores also improved in both groups, with a slightly greater improvement in the anxiety score in the T4-plus-T3 group. Well-being increased in 26 percent of the patients in the T4-plus-T3 group and 29 percent of those in the T4 group. At 12 months, the initial differences favoring therapy with T4 plus T3 were no longer present. All other questionnaire results were similar to those at three months and not different between the two groups.
The conclusions of the study. Among patients with hypothyroidism, T4-plus-T3 therapy (ratio, 5:1 to 15:1) was slightly more effective than T4 alone; the benefit was not sustained.
The original article. Saravanan P, Simmons DJ,
Greenwood R, Peters TJ, Dayan CM. Partial substitution of thyroxine
(T4) with tri-iodothyronine in patients on T4 replacement therapy:
results of a large community-based randomized controlled trial.
J Clin Endocrinol Metab 2005;90:805-12.
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