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Submitted on February 8, 2007
Accepted on August 10, 2007
Division of Endocrinology and Diabetes, Medicine II, University Hospital Freiburg, Medizinische Klinik Innenstadt, University Hospital Innenstadt, Ludwig-Maximilians-University, Munich; Department of Psychology, Albert-Ludwigs University, Freiburg, and University Hospital Bern, FPD, University of Bern; Clinical Pharmacy, University Hospital Freiburg; Department of Clinical Chemistry, University Hospital Freiburg; and Department of Medical Biometry and Statistics, University Hospital Freiburg
* To whom correspondence should be addressed. E-mail: Martin.Reincke{at}med.uni-muenchen.de.
Background: Dosage of thyroxine (T4) in central hypothyroidism is primarily guided by fT4. However, the optimum fT4 range is ill-defined, and subtle hypothyroidism might be missed using this approach.
Objectives: To investigate the effects of a body weight-adapted (bw) T4 treatment — alone or in combination with T3 — on metabolism, well-being and cognitive function in comparison to a regimen leading to normal fT4.
Design: Placebo controlled trial (double blind, crossover).
Patients: 29 patients (age: 52 ± 2; f/m: 8/21) with hypopituitarism including TSH deficiency.
Interventions: Three regimens were compared (5 weeks each): "EMPIRICAL-T4", empirical T4 dosage (1 ± 0.05 µg/kg bw) leading to normal fT4; "BW-ADAPTED-T4", body weight-adapted T4 (1.6 µg/kg bw T4); "BW-ADAPTED-T3T4", bw-adapted combination of T3 and T4 (ratio of 1:10).
Results: BW-ADAPTED-T4 administration increased mean fT4 concentrations to the upper limit of the normal range (peak levels). Compared to EMPIRICAL-T4, BW-ADAPTED-T4 treatment resulted in a lower BMI (29.0 ± 0.7 vs. 29.5 ± 0.7 kg/m2; P < 0.03), lower total cholesterol (198 ± 9 vs. 226 ± 7; P < 0.01) and lower LDL cholesterol (116 ± 5 vs. 135 ± 7 mg/dl; P < 0.01). BW-ADAPTED-T3T4 treatment was associated with additional beneficial effects on ankle reflex time and working memory, but resulted in supraphysiologic fT3 levels.
Limitations: Long-term side effects may have been missed.
Conclusion: Using a dose of 1.6 µg/kg bw improved markers commonly associated with central hypothyroidism. This suggests that T4 dosage based on body weight and aiming at fT4 in the upper reference range is superior to titration of thyroxine aiming at middle normal fT4 concentrations in those patients.
Trial Registration: clinicaltrials.gov; Identifier: NCT00360074
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