Benefit of Combined Triiodothyronine (LT₃) and Thyroxine (LT₄) Treatment in Athyreotic Patients Unresponsive to LT₄ Alone

Abstract

Despite some reports, the usefulness of levothyroxine ( LT₄) and levotriiodothyronine (LT₃) combination therapy in hypothyroidism remains controversial. The objective of this paper is to study a benefit of additional LT₃ in athyreotic patients who failed to normalize TSH on LT₄ alone even with hyperthyroid serum T₄ values.

In a survey of 200 athyreotic patients treated between 2006 and 2009, about 7% failed to normalize serum TSH levels following treatment with LT₄, though serum T₄ values in the hyperthyroid range were achieved. These patients (characterized by serum T₄≥160 nmol/L and TSH≥5.0 mIU/L), were additionally treated with 10 μg b. i. d LT₃. LT₃ and LT₄ combination therapy resulted in decreased serum TSH levels into the normal range (12.8 vs. 1.22 mIU/L; p<0.01) and reduced LT₄ dose (153.3 vs. 117.5 μg; p<0.01) required for normalization of serum T₄ values (170.6 vs. 123.3 nmol/L; p<0.01). Serum T₃ values were higher (1.3 vs. 2.26 nmol/L; p<0.01) than those during monotherapy with LT₄.

Our results indicate a subpopulation of athyreotic patients that could significantly benefit from combined LT₄ + LT₃ therapy in restoring normal TSH and thyroid hormone patterns. Further research should be undertaken to provide a genetic basis for these findings.

Key words

thyrotropin - insufficiencies - thyroid

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