Twenty-four Hour Hormone Profiles of TSH, Free T3 and Free T4 in Hypothyroid Patients on Combined T3/T4 Therapy
- 1 April 2007
- journal article
- research article
- Published by Georg Thieme Verlag KG in Experimental and Clinical Endocrinology & Diabetes
- Vol. 115 (04), 261-267
- https://doi.org/10.1055/s-2007-973071
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.Keywords
This publication has 19 references indexed in Scilit:
- Replacement therapy with levothyroxine plus triiodothyronine (bioavailable molar ratio 14 : 1) is not superior to thyroxine alone to improve well-being and cognitive performance in hypothyroidismClinical Endocrinology, 2004
- 3-Iodothyronamine is an endogenous and rapid-acting derivative of thyroid hormoneNature Medicine, 2004
- Combined Levotriiodothyronine and Levothyroxine Therapy for Hypothyroidism: Are We a Step Closer to the Magic Formula?Thyroid®, 2004
- Thyroxine Plus Low-Dose, Slow-Release Triiodothyronine Replacement in Hypothyroidism: Proof of PrincipleThyroid®, 2004
- Combined T4 and T3 Therapy—Back to the Drawing BoardJama-Journal Of The American Medical Association, 2003
- Dissatisfaction with thyroxine therapy — could the patients be right?Current Opinion in Pharmacology, 2002
- Psychological well-being in patients on 'adequate' doses of L-thyroxine: results of a large, controlled community-based questionnaire studyClinical Endocrinology, 2002
- Thyroxine vs Thyroxine Plus Triiodothyronine in Treatment of Hypothyroidism After Thyroidectomy for Graves' DiseaseEndocrine, 2002
- Risk for Fracture in Women with Low Serum Levels of Thyroid-Stimulating HormoneAnnals of Internal Medicine, 2001
- Effects of Thyroxine as Compared with Thyroxine plus Triiodothyronine in Patients with HypothyroidismThe New England Journal of Medicine, 1999