Timing of breakfast does not influence therapeutic efficacy of liquid levothyroxine formulation
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Oral levothyroxine (L-T4) is the mainstay of hypothyroidism treatment. Many factors may influence its absorption, including the timing of administration. Objective of the study is to demonstrate the therapeutic equivalence of administering liquid L-T4 with breakfast or 10 min before breakfast. This was a pilot study conducted with a crossover design AB/BA where A stays for L-T4 with breakfast and B for L-T4 10 min before breakfast. A post hoc analysis was conducted to compare L-T4 administered at breakfast or 10 min before breakfast with L-T4 administered 30 min before breakfast. Sixty-one hypothyroid patients were enrolled and assigned to one of the two treatment sequences. All patients were evaluated for TSH levels at the end of each period. Fifty-nine patients completed the study. The mean thyrotropin concentration was 1.52 ± 0.73 µU/ml when L-T4 was administered with breakfast and 1.46 ± 0.81 µU/ml when it was taken 10 min before breakfast, without clinically and statistically significant differences (P = 0.59), regardless of treatment sequence and period. The mean thyrotropin concentration was 1.54 ± 0.9 µU/ml when L-T4 was administered at 0–10 min intervals before breakfast and 1.25 ± 0.7 µU/ml when it was taken 30 min before breakfast (ratio = 1.23, within our definition of equivalence set at 0.8–1.25). There is therapeutic equivalence between liquid L-T4 administration at breakfast or 10 min before breakfast. We can also hypothesize that there are no clinically relevant differences between liquid L-T4 administration 30 min before breakfast or at shorter intervals.
KeywordsLevothyroxine Oral solution Hypothyroidism Replacement therapy TSH Therapeutic equivalence
The authors would like to thank the nurse team (Nadia Biccari, Alberto Pambianco, and Lorena Urbani) of the Endocrine Clinic at the Department of Medicine, University of Perugia, for their excellent assistance. This research did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
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Conflict of interest
The authors declare that they have no conflict of interest.
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