• Nersi Alaeddin, Rutchanna M S Jongejan, Julia C Stingl, Yolanda B de Rijke, Robin P Peeters, BretelerMonique M BMMB, and Folgerdiena M de Vries.
• Population Health Sciences, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany; Department of Clinical Chemistry, Erasmus MC University Medical Center, Rotterdam, The Netherlands; Department of Internal Medicine, Erasmus MC University Medical Center, Rotterdam, The Netherlands; Institute of Clinical Pharmacology, Faculty of Medicine, RWTH Aachen, Germany; Academic Centre for Thyroid Diseases, Erasmus MC University Medical Center, Rotterdam, The Netherlands; Institute for Medical Biometry, Informatics and Epidemiology (IMBIE), Faculty of Medicine, University of Bonn, Bonn, Germany.
• Dtsch Arztebl Int. 2023 Oct 20; 120 (42): 711718711-718.

BackgroundLevothyroxine is a very commonly prescribed drug, and treatment with it is often insufficient or excessive. Nonetheless, there have been only a few reports on the determinants of inadequate levothyroxine treatment.MethodsData from 2938 participants in the population-based Rhineland Study were analyzed. Putative determinants of inadequate levothyroxine treatment (overtreatment, thyrotropin level <0.56 mU/L; undertreatment, thyrotropin level >4.27 mU/L) were studied with logistic regression. The determinants of the levothyroxine dose were assessed with linear regression.ResultsOverall, 23% of the participants (n = 662) stated that they were taking levothyroxine. Among these participants, 18% were overtreated and 4% were undertreated. Individuals over 70 years of age and above were four times as likely to be overtreated (OR = 4.05, 95% CI [1.20; 13.72]). Each rise in the levothyroxine dose by 25 μg was associated with an increased risk of overtreatment (OR = 1.02, 95% CI [1.02; 1.03]) and of undertreatment (OR = 1.02, 95% CI [1.00; 1.03]). Well-controlled participants (normal thyrotropin levels 0.56-4.27 mU/L) received a lower levothyroxine dose (1.04 ± 0.5 μg/kg/d) than overtreated (1.40 ±0.5 μg/kg/d) or undertreated (1.37 ±0.5 μg/kg/d) participants. No association was found between sociodemographic factors or comorbidities and the levothyroxine dose. Iodine supplementation was associated with a lower daily dose (β = -0.19, 95% CI [-0.28; -0.10]), while three years or more of levothyroxine exposure was associated with a higher daily dose (β = 0.24, 95% CI [0.07; 0.41]).ConclusionLevothyroxine intake was high in our sample, and suboptimal despite monitoring. Our findings underscore the need for careful dosing and for due consideration of deintensification of treatment where appropriate.

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