Comment on: “Levothyrox® New and Old Formulations: Are they Switchable for Millions of Patients?”
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I read with interest the article published in Clinical Pharmacokinetics by Didier Concordet and colleagues , who reported an independent revised statistical analysis of the bioequivalence study between old and new formulations of Levothyrox® . Using the approach of individual bioequivalence (IBE) instead of average bioequivalence (ABE), more than 50% of healthy volunteers enrolled in this bioequivalence study were outside the a priori bioequivalence range and thus the authors questioned whether the switchability of these two drugs was a safe option in patients. Meanwhile, a ‘Levothyrox scandal’ has legitimately agitated the French public and media due to an unexpectedly large number of adverse events occurring soon after the launch of the new formulation. In this sensitive context, the conclusion of this reanalysis could be falsely interpreted and therefore counterproductive. So, I feel the need to raise some major concerns. First, their article perfectly illustrates a decade of...
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No external funding was used in the preparation of this letter.
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Patrick Nicolas declares no potential conflicts of interest relating to this letter.
- 1.Concordet D, Gandia P, Montastruc J-L, Bousquet-Mélou A, Lees P, Ferran A, et al. Levothyrox® new and old formulations: are they switchable for millions of patients? Clin Pharmacokinet. Epub 2019 Apr 4. https://doi.org/10.1007/s40262-019-00747-3.
- 3.Guidance for Industry. Draft guidance on levothyroxine sodium. https://www.accessdata.fda.gov/drugsatfda_docs/psg/Levothyroxine_draft_Oral tab_RLD 021116 021210 021301 021342 321402_RC12-14.pdf. Accessed 24 May 2019.
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