Endocrine Abstracts

Introduction: 90-95% of patients with primary hypothyroidism respond well to levothyroxine (L-T4) therapy. A minority remain symptomatic despite optimised L-T4 therapy. There is limited evidence supporting the role of liothyronine (L-T3) in this subgroup of patients. By looking at 3- and 6-month trials, we aim to review our practice of L-T4/l-T3 therapy.

Method: We reviewed medical and pharmacy records of all patients receiving L-T4/l-T3 therapy from January-2019 to July-2022. Data were collected and tabulated from clinic letters, pharmacy and ICE software.

Result: 15 patients were identified – 12 (80%) females, mean age 51.3 years (29-63). Baseline mean TSH was 1.12 mU/l (range <0.01-5.68) but only 6 (40%) within reference, with 7 (46.7%) low TSH indicating overtreatment. Pre-trial, the mean L-T4 dose was 118.6 mg (75-187.5 mg od). The modal L-T3 starting dose (8 patients) was 10 mg bd (range 5 mg od–10 mg tds), and all had a concomitant reduction in L-T4 dose. At 3 months, patients’ subjective symptom reports yielded that 9 (60%) felt an improvement in symptoms, 4 (26.7%) felt no improvement, and 2 (13.3%) experienced side effects. TSH level as a guide to thyroid status showed 5 (33.3%) within, 2 (13.3%) above and 8 (53.3%) below the reference range. Accounting for one outlier (TSH 23.85), the mean TSH was 1.08 mU/l (0.01-5.79). 6 patients required follow up to 6 months, 2 with normal TSH, 2 low, and 2 awaited. Mean TSH was 0.77 (0.04-1.43). After trial completion, 8 (53.3%) patients continued combination therapy in primary care, 5 (33.3%) changed back to L-T4 monotherapy. 2 patients are awaiting review.

Discussion: A majority of patients had marked improvement in symptoms after L-T3/l-T4 combination therapy & able to maintain euthyroid status, demonstrating that careful use of combination therapy may benefit a select group of cases. However, further large studies are required to fully explore this potential.