Exp Clin Endocrinol Diabetes 2007; 115(4): 261-267
DOI: 10.1055/s-2007-973071
Article

© J. A. Barth Verlag in Georg Thieme Verlag KG · Stuttgart · New York

Twenty-four Hour Hormone Profiles of TSH, Free T3 and Free T4 in Hypothyroid Patients on Combined T3/T4 Therapy

P. Saravanan 1 , H. Siddique 2 , D. J. Simmons 1 , R. Greenwood 3 , C. M. Dayan 1
  • 1Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol
  • 2Department of Endocrinology, Bristol Royal Infirmary, Bristol, UK
  • 3Research and Development Support Unit, Bristol Royal Infirmary, Bristol, UK
Further Information

Publication History

received 3. 8. 05 first decision 4. 11. 05

accepted 3. 11. 06

Publication Date:
03 May 2007 (online)

Abstract

The benefits of using thyroxine (T4) plus triiodothyronine (T3) in combination in thyroid hormone replacement are unproven but many individuals continue to be treated with this regime. When T3 is used alone for hypothyroidism, it results in wide fluctuations of thyroid hormone levels. However, only limited data exists on combined T3/T4 therapy. In this study, we have compared 24-hour profiles of thyroid stimulating hormone (TSH), free T4 (fT4) and free T3 (fT3) and cardiovascular parameters in 10 hypothyroid patients who had been on once daily combined T3/T4 therapy for more than 3 months with 10 patients on T4 alone. Twenty patients, who were part of a larger study, investigating the long-term benefits of combined T3/T4 therapy, were recruited into this sub-study. Over 24-hours, 12 samples were taken for thyroid hormones. Their 24-hour pulse and BP is also monitored on a separate occasion. On T4 alone, a modest 16% rise in fT4 with no change in fT3 was seen in the first 4-hours post-dose. In contrast, on combined treatment, fT3 levels showed a marked rise of 42% within the first 4-hours post-dose (T3/T4:T4=6.24: 4.63 mU/L, p<0.001). Mean exposure to fT3 calculated by area under the curve (AUC) was higher (T3/T4:T4=1148:1062, p<0.0001) on T3. Circadian rhythm of TSH was maintained on both treatments. No difference in pulse or blood pressure over the 24-hours was seen between the groups. Our data suggests that despite chronic combined T3/T4 therapy, wide peak-to-trough variation in fT3 levels persists. Although no immediate cardiovascular effects were seen, the long-term consequences for patients on combined therapy are unknown.

References

1 Financial support: Southwest National Health Service Research and Development, UK.

Correspondence

C. M. Dayan

Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology

Dorothy Hodgkin Building

University of Bristol

Whitson St

Bristol BS1 3NY

UK

Phone: +44/117/92 82 271

Fax: +44/117/92 84 081

Email: [email protected]