ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P771

Thyroid hormone replacement using a combination of levothyroxine plus slow-release liothyronine: beyond proof of principle

Gerald JM Tevaarwerk

University of Western Ontario, London, Ontario, Canada.

Objective: To assess if adding slow-release liothyronine (SR-T3) to levothyroxine (l-T4) reduces persistent hypothyroid symptoms and signs on replacement with l-T4 alone.

Design: Open label, two-period cross-over, cohort comparison. The main outcomes were changes in the serum T3 concentration and residual clinical hypothyroid indicants. Each study period was 10 weeks. The sample size required was determined to be 9 patients.

Subjects: Three men and 15 women, aged 31 to 72, with primary, autoimmune hypothyroidism who had persistent hypothyroid indicants in spite of normal or suppressed thyroid stimulating hormone (TSH) levels on l-T4 alone entered the study after giving informed consent.

Methods: Subjective clinical indicants, scored as ordinals from 0 to 3, and objective clinical and biochemical indicants measured on a numerical scale, were compared during treatment with l-T4 alone to treatment with l-T4 plus SR-T3 titrated to an increase in the serum T3 of 0.50 pmol/l.

Main outcome: Adding an average of 13 (range 5–20) μg per day of SR-T3 elevated the serum T3 by a significant average (95% CI) of 0.80 (0.60–1.00) pmol/l. The mean clinical hypothyroid indicant score (95% CI) of 13.9 (10.8–17) on monotherapy, fell by a significant average of 10.8 (9.0–12.6) (84 (70.3–97.3) percent) to 3.3 (0.9–5.5). The T4/T3 ratio fell significantly from 4.0 (3.7–4.3) to 3.5 (3.1–3.7). There were no significant changes in the initial mean l-T4 dose of 88 (74–102), or mean TSH of 1.5 (0.9–2.1) mU/l and T4 of 16.3 (15.2–17.4) pmol/l. No patient exhibited evidence of over-replacement.

Conclusion: Treating primary, autoimmune hypothyroid patients with persistent hypothyroid symptoms and signs using a combination of l-T4 plus SR-T3 resulted in a significant rise in the serum T3 level and decrease in the persistent hypothyroid indicants.

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