(15.03) Impact of Switching among Different Brands of Levothyroxine Tablet on Maintaining Normal Thyrotropin Levels: Results of a Prospective, Multicenter, Phase IV clinical trial

In this prospective, multicenter, phase IV clinical trial conducted at six centers in India, patients were enrolled from May 2022 to May 2023. Adults aged 18 to 65 years (both inclusive), diagnosed with primary hypothyroidism for ≥1 year duration, receiving a stable dose of levothyroxine tablet [Thyronorm (manufactured by Abbott India Ltd.) or Eltroxin (manufactured by GlaxoSmithKline Pharmaceuticals Ltd.)] for atleast last 8 weeks and having normal serum TSH levels (0.465 to 4.68 mIU/L), were included. All patients were switched to Lethyrox tablet (manufactured by Intas Pharmaceuticals Ltd.) at the same dose that they were receiving earlier, for a total duration of 18 weeks. Patients were excluded if they were pregnant, had diagnosed panhypopituitarism or secondary hypothyroidism, or had a medical condition or used medications that could affect thyrotropin levels. The primary outcome was the proportion of patients that maintained normal serum TSH after 6 weeks of switch. Secondary endpoints included the proportion of patients that maintained normal serum TSH values after 12 and 18 weeks of switch respectively and the proportion of patients that did not need a change of dose after switch at 6, 12 and 18 weeks. 

Results:

One hundred and fifty patients were enrolled, with mean (± SD) age of 45 (±11) years including 69.3% females and 30.7% males and mean (±SD) serum TSH value at baseline of 2.49 (±1.12) mIU/L. 142 patients qualified for intent-to-treat (ITT) analysis. 78.2% (111) of patients obtained normal serum TSH values after 6 weeks of switching to Lethyrox tablet. The serum TSH level was within normal reference range for 73.2% (104) patients and 76.1% (108) patients at 12 and 18 weeks after switch respectively. A dose change was not required in ~91% patients after switching to Lethyrox tablet at weeks 6 and 12 respectively. The mean (± SD) TSH values at 6, 12 and 18 weeks were 3.55 (±7.90), 3.71 (±4.83) and 3.00 (±2.03) mIU/L, respectively. The mean absolute change of TSH values from baseline to 6, 12 and 18 weeks of treatment was 1.01 (± 8.1), 1.23 (± 5.02) and 0.52 (± 2.24) mIU/L, respectively. No adverse effects were reported during the study.

Discussion/Conclusion:

Switching among different brands of Levothyroxine tablet was not associated with clinically significant changes in serum TSH levels in majority of patients with primary hypothyroidism and was safe.