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A Randomized, Masked Study of Triiodothyronine Plus Thyroxine Administration in Preterm Infants Less Than 28 Weeks of Gestational Age: Hormonal and Clinical Effects

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A Randomized, Masked Study of Triiodothyronine Plus Thyroxine Administration in Preterm Infants Less Than 28 Weeks of Gestational Age: Hormonal and Clinical Effects 0031-3998/04/5502-0248 PEDIATRIC RESEARCH Vol. 55, No. 2, 2004 Copyright © 2004 International Pediatric Research Foundation, Inc. Printed in U.S.A. A Randomized, Masked Study of Triiodothyronine Plus Thyroxine Administration in Preterm Infants Less Than 28 Weeks of Gestational Age: Hormonal and Clinical Effects PAOLO G. VALERIO, ALEID G. VAN WASSENAER, JAN J.M. DE VIJLDER, AND JOKE H. KOK Department of Neonatology [P.G.V., A.G.v.W., J.H.K.] and Laboratory of Pediatric Endocrinology [J.J.M.d.V.], Academic Medical Center, Emma Children’s Hospital, 1105 AZ Amsterdam, The Netherlands ABSTRACT A randomized, placebo-controlled, masked study was con- effect on cortisol levels. We did not find any effects of T3 or of ducted of the responses of thyroid parameters, cortisol, and the T4 administration on the cardiovascular system. A single injec- ␮ cardiovascular system to a single dose of triiodothyronine (T3) tion of T3 (0.5 g/kg) given 22–26 h after birth only leads to a 24 h after birth, followed by a daily dose of thyroxine (T4) during 2-d increase of T3 levels and does not have effects on the Ͻ 6 wk to infants 28 wk gestational age. Thirty-one infants were cardiovascular system. This study does not support the use of T3 assigned to three groups: 1) group A: T3 24 h after birth plus according to our regimen in preterm infants. (Pediatr Res 55: daily T4 during 6 wk; 2) group B: placebo T3 and T4 during 6 wk; 248–253, 2004) and 3) group C: placebo T3 and placebo T4.T4, free T4,T3, free T3, reverse T3, thyroid-stimulating hormone, and cortisol were measured in cord blood and on days 1, 3, 7, 14, 21, 42, and 56. Abbreviations Data on pulse rate, blood pressure, and cumulative dose of T3, triiodothyronine ␮ inotropic agents were collected. T3 (0.5 g/kg) resulted in a T4, thyroxine plasma increase until day 3. Thereafter, plasma T3 levels were TSH, thyroid-stimulating hormone comparable between the groups. T4, free T4, and reverse T3 were GA, gestational age increased in groups A and B during the period of T4 adminis- rT3, reverse T3 tration. Thyroid-stimulating hormone suppression was of shorter FT4, free T4 duration in group A. T3 and T4 administration did not have any FT3, free T3 Thyroid hormones play an important role in normal growth immaturity of the hypothalamo-pituitary-thyroid axis and the and development of the CNS (1, 2). In term infants, thyroxine sudden interruption of the maternal contribution to fetal thyroid (T4) and triiodothyronine (T3) increases shortly after birth. In hormone pools are involved. Thyroid hormone supplementa- premature infants, transient hypothyroxinemia after birth is a tion in preterm infants has been the subject of several clinical common finding (3–7). This hypothyroxinemia is characterized studies with clinical and neurodevelopmental parameters as by low levels of T4 and T3, which do not cause elevations in primary outcome (12–14). To date, no clear effect of supple- thyroid-stimulating hormone (TSH) above 20 mU/L. The de- mental T4 treatment on neurodevelopmental outcome has been gree of hypothyroxinemia is related to gestational age (GA) demonstrated. In an earlier study, however, we observed that a and the severity of neonatal disease. Low T and T levels in Ͻ 3 4 subgroup of T4-treated infants of 29 wk GA tended to have premature infants have been found to be associated with poor a better developmental outcome than infants of similar GA in neurologic and developmental outcome (8–11). the placebo group (13, 15). Transient hypothyroxinemia is a multicausal phenomenon in Ͻ T4 administration to preterm infants of 30 wk GA did not which immaturity of thyroid hormone metabolism with high result in increased plasma T3 levels; in fact, it resulted in de- activity of deiodinase type 3 together with factors such as creased plasma T3 levels and increased plasma reverse T3 (rT3) levels (16). It was suggested that this T3 decrease was caused by Received February 17, 2003; accepted July 4, 2003. lower endogenous thyroidal T production as a result of TSH Correspondence: Aleid G. van Wassenaer M.D., Ph.D., Department of Neonatology, 3 Emma Children’s Hospital AMC, Meibergdreef 9, 1105 AZ Amsterdam, The Nether- suppression and that, because of low thyroidal and hepatic type 1 lands; e-mail: [email protected] deiodinase activity and high deiodinase type 3 activity, an increase DOI: 10.1203/01.PDR.0000104153.72572.F5 in plasma T4 did not result in an increase in plasma T3. 248 T3 PLUS T4 ADMINISTRATION IN PRETERMS 249 ␮ Although the T3 decrease after T4 administration did not in a single i.v. dose of 0.5 g/kg 22–26 h after birth. T4 was ␮ result in worse clinical outcome, a T3 increase shortly after given in a daily i.v. dose of 8 g/kg during 42 d starting birth could very well improve clinical outcome. We hypothe- immediately after the single dose of T3. As in previous studies sized that a single dose of T3 is able to switch on deiodinating of our group (13, 17), T4 was given by enteral route when all enzymes and thus simulate the rapid postnatal increase of T3 feeding was given enterally. levels as is especially seen in more mature infants. This Thyroid hormone and cortisol determinations. The primary increase in T3 levels is thought to be necessary for metabolic outcome was thyroid function measured as plasma levels of T4, adaptation after birth. free T4 (FT4), T3, free T3 (FT3), rT3, TSH, and plasma cortisol In an earlier study using historical controls, we described levels. Blood samples (1 mL) were taken from cord blood 24 h that a single dose of T3 12 h after birth resulted in a sustained after birth (just before T3 administration) and again on days 3, increase of plasma T3 both if given as a single treatment and in 7, 14, 21, 42, and 56. Furthermore, 0.3-mL blood samples were combination with 6 wk of T4 supplementation. Because this taken 30, 120, and 360 min after T3 administration for deter- study was done with a historical control group, these results mination of T3 levels. need to be reproduced in a randomized trial (17). T4,T3, and rT3 were measured by in-house RIA methods. The aim of the current study was to investigate the hormonal FT3,FT4, and TSH were measured by time-resolved fluoroim- effects of three supplementation schemes (T4 plus T3,T4 plus munoassay (DelfiaFT4, respectively, DelfiaFT3 and Delfia placebo, and placebo) in a randomized, masked way in infants hTSH Ultra; Wallac Oy, Turku, Finland). Cortisol was mea- Ͻ28 wk GA. In addition, we measured plasma cortisol levels sured by luminescence enzyme immunoassay (Immulite; Di- concurrently with thyroid hormone levels. This was done agnostic Products Corporation, Los Angeles, CA, U.S.A.) because, to our knowledge, until now, there are no reports on Detection limits were as follows: T4, 5 nmol/L; T3, 0.3 the influence of transient hypothyroxinemia in preterm infants nmol/L; rT3, 0.03 nmol/L; FT3, 1 pmol/L; FT4, 2 pmol/L; TSH, on adrenal cortex function, whereas glucocorticoid hormones 0.01 mU/L; and cortisol, 30 nmol/L. Intra-assay variations Ϯ and thyroid hormones are known to be functionally interrelated were as follows: T4,2–4%; T3,3–4%; rT3,4–5%; FT3, 6%; with respect both to maturational effects and to influencing FT4,4–6%; TSH, 1–2%; cortisol, 3.6–6.4%. Interassay vari- each other’s regulatory pathways (18, 19). ations were as follows: T4,3–6%; T3,7–8%; rT3,5–9%; FT3, Ϯ In several pediatric studies, it has been suggested that T3 9%; FT4,5–8%; TSH, 3–4%; cortisol, 4.7–9.0%. administration improves myocardial function, especially after Cardiovascular measurements. Secondary outcomes were cardiac surgery (20–22). In an earlier study, we found higher daily mean heart rate, daily mean intra-arterial blood pressure heart rates in children who received only T4 (23). For studying during the first week of life, and cumulative dose of inotropic the effects of T3 plus T4 administration on the cardiovascular agents. These data all were collected prospectively. Daily mean system, intra-arterial blood pressure, heart rates, and cumula- heart rate and intra-arterial blood pressure were calculated as tive doses of inotropic agents were measured in all infants the mean of four values at predefined time points (0400, 1000, included in the current study. 1600, and 2200 h). Cumulative doses of inotropic agents were calculated over the total study period and each of the first4d METHODS after T3 administration separately. Statistical analysis. Data analysis was done using SPSS Eligibility and randomization. This study was approved by version 10.0.7 (SPSS Inc., Chicago, IL, U.S.A.). The one-way the Committee of Medical Ethics of the Academic Medical ANOVA with Bonferroni post hoc analysis was used to com- Center in Amsterdam (The Netherlands) and by the National pare continuous variables in the three study groups. For anal- Committee on Human Research. Infants who were admitted to ysis of categorical data, the ␹2-test (3 ϫ 2 tables) was used. our neonatal intensive care unit and were born between Sep- Statistical significance was set at p ϭ 0.05. tember 2000 and September 2001 with a GA Ͻ28 wk were eligible for the study. Infants were excluded when they had a RESULTS severe congenital anomaly or when there was maternal endo- crine disease. When informed consent had been obtained from Patients.
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