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Initiation of therapy with a full dose of thyroxine in patients with hypothyroidism is safe, but not effective sooner than a low dose
The background of the study. Most patients with
hypothyroidism are treated with thyroxine (T4), but there is debate
about whether the starting dose should be the dose patients are
likely to need long term (replacement dose) or considerably lower.
In this study, the effects of starting T4 with a replacement dose
and a low dose were compared in patients with hypothyroidism.
How the study was done. Fifty patients with overt hypothyroidism (high serum thyrotropin [TSH] and low free T4 concentrations) were randomly assigned to receive T4 in a dose of 1.6 µg/kg/day (full-dose group) or 25 µg/day (low-dose group). In both groups, the doses were adjusted in increments of 25 µg every 4 weeks for 6 months and then every 12 weeks for 6 months, with the goal of achieving normal serum TSH and free T4 concentrations. At base line and the times described above, the patients completed questionnaires about symptoms and well-being, and serum TSH and free T4 were measured.
The results of the study. In the full-dose group, the mean daily T4 dose increased from 128 µg (1.6 µg/kg) to 139 µg (1.7 µg/kg). In the low-dose group, the dose was increased regularly for 16 weeks, at which time it was 110 µg (1.5 µg/kg) daily, and did not change thereafter. At base line, the serum TSH concentrations were high (median, 61 and 48 mU/L, respectively) in the full-dose and low-dose groups, and the respective values at 4 weeks were 4.2 and 26.7 mU/L. The values in the full-dose group did not change thereafter, whereas the values in the low-dose group continued to decline. In the full-dose group, serum free T4 concentrations increased substantially at 4 weeks, but changed little thereafter, whereas they increased slowly in the low-dose group, reaching the same level as in the full-dose group at 16 weeks. The scores on the questionnaires improved at the same rate and reached the same final values (at 24 weeks) in both groups. There were no deleterious effects of the full dose.
The conclusion of the study. In patients with hypothyroidism, starting therapy with a full dose of T4 is safe, but not more effective in relieving symptoms than starting with a low dose.
The original article. Roos A, Linn-Rasker SP, van Domburg RT, Tijssen JP, Berghout A. The starting dose of levothyroxine in primary hypothyroidism treatment: a prospective, randomized, double-blind trial. Arch Intern Med 2005;165:1714-20. (Erratum, Arch Intern Med 2005;165:2227.)
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| Thyroid Digest Index | | | November 2005 Thyroid Digest |
