Comment on: Levothyrox® New and Old Formulations: Are They Switchable for Millions of Patients?
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I read with particular interest the article by Concordet et al.  entitled “Levothyrox® new and old formulations: are they switchable for millions of patients?”, which was recently published in Clinical Pharmacokinetics. We must now propose pharmacological hypotheses in order to understand the origin of these adverse effects, and subsequently learn lessons for the future.
In March 2017, a new formula (NF) of levothyroxine (a drug with a narrow therapeutic index) was introduced onto the French market by Merck Santé Laboratories. Shortly thereafter, a very significant increase in adverse reactions (memory loss, palpitations, fatigue, weight gain, dizziness, etc.) was reported by patients (some of whom were not informed there had been a NF) to the French National Agency for Medicines and Health Products Safety (ANSM). Surprisingly, only the excipients had been modified in the levothyroxine NF, with lactose being replaced by the ‘well-known’ mannitol (the filler) and citric...
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Conflict of interest
Philippe Tréchot declares no potential conflicts of interest that might be relevant to the contents of this letter.