Endocrine Abstracts

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.