Clinical Pharmacokinetics

, Volume 58, Issue 7, pp 959–960 | Cite as

Comment on: “Levothyrox® New and Old Formulations: Are they Switchable for Millions of Patients?”

  • Patrick NicolasEmail author
Letter to the Editor

I read with interest the article published in Clinical Pharmacokinetics by Didier Concordet and colleagues [1], who reported an independent revised statistical analysis of the bioequivalence study between old and new formulations of Levothyrox® [2]. 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...


Compliance with Ethical Standards


No external funding was used in the preparation of this letter.

Conflict of interest

Patrick Nicolas declares no potential conflicts of interest relating to this letter.


  1. 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.
  2. 2.
    Gottwald-Hostalek U, Uhl W, Wolna P, Kahaly GJ. New levothyroxine formulation meeting 95-105% specification over the whole shelf-life: results from two pharmacokinetic trials. Curr Med Res Opin. 2017;33:169–74.CrossRefPubMedGoogle Scholar
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    Jiang W, Makhlouf F, Schuirmann DJ, Zhang X, Zheng N, Conner D, et al. A bioequivalence approach for generic narrow therapeutic index drugs: evaluation of the reference-scaled approach and variability comparison criterion. AAPS J. 2015;17(4):891–901.CrossRefPubMedPubMedCentralGoogle Scholar
  5. 5.
    Peeters RP, Visser TJ. Metabolism of thyroid hormone [Updated 2017 Jan 1]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext. South Dartmouth:, Inc.; 2000. Accessed 24 May 2019.

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Service de Biochimie, Unité de Pharmacologie BiocliniqueCentre Hospitalier Universitaire Avicenne (APHP)Bobigny CedexFrance

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