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Levothyroxine

What works?

Learn more about the effects of these drugs. The most reliable research is summed up for you in our featured article.

By mouth

Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine is also used… Read more

Brand names include: Levothroid, Levoxyl

By injection

Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine injection can… Read more

Brand names include: Synthroid, levothyroxine sodium Novaplus

Drug classes About this
Diagnostic Agent, Thyroid Function, Endocrine-Metabolic Agent, Thyroid Supplement

What works? Research summarized

Evidence reviews

Levothyroxine treatment and pregnancy outcome in women with subclinical hypothyroidism undergoing assisted reproduction technologies: systematic review and meta-analysis of RCTs

BACKGROUND Previous meta-analyses of observational data indicate that pregnant women with subclinical hypothyroidism have an increased risk of adverse pregnancy outcome. Potential benefits of levothyroxine (LT4) supplementation remain unclear, and no systematic review or meta-analysis of trial findings is available in a setting of assisted reproduction technologies (ART). METHODS Relevant trials published until August 2012 were identified by searching MEDLINE, EMBASE, Web of Knowledge, the Cochrane Controlled Trials Register databases and bibliographies of retrieved publications without language restrictions. RESULTS From 630 articles retrieved, we included three trials with data on 220 patients. One of these three trials stated 'live delivery' as outcome. LT4 treatment resulted in a significantly higher delivery rate, with a pooled relative risk (RR) of 2.76 (95% confidence limits 1.20-6.44; P = 0.018; I(2) = 70%), a pooled absolute risk difference (ARD) of 36.3% (3.5-69.0%: P = 0.030) and a summary number needed to treat (NNT) of 3 (1-28) in favour of LT4 supplementation. LT4 treatment significantly lowered miscarriage rate with a pooled RR of 0.45 (0.24-0.82; P = 0.010; I(2) = 26%), a pooled ARD of -31.3% (-48.2 to -14.5%: P < 0.001) and a summary NNT of 3 (2-7) in favour of LT4 supplementation. LT4 treatment had no effect on clinical pregnancy (RR 1.75; 0.90-3.38; P = 0.098; I(2) = 82%). In an ART setting, no data are available on the effects of LT4 supplementation on premature delivery, arterial hypertension, placental abruption or pre-eclampsia. CONCLUSIONS Our meta-analyses provide evidence that LT4 supplementation should be recommended to improve clinical pregnancy outcome in women with subclinical hypothyroidism and/or thyroid autoimmunity undergoing ART. Further research is needed to determine pregnancy outcome after close monitoring of thyroid function to maintain thyroid-stimulating hormone and free T4 levels within the trimester-specific reference ranges for pregnancy.

Does perioperative thyroxine have a role during adult cardiac surgery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether the use of prophylactic perioperative thyroxine therapy during cardiopulmonary bypass in the euthyroid adult patient undergoing routine cardiac surgery can result in an improved cardiac output leading to better clinical outcomes. Altogether 86 papers were identified on Medline and 113 on Embase using the reported search. A further paper was identified by hand-searching of reference lists. Thirteen papers represented the best evidence on the topic. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses were tabulated. We conclude that it is clear that triiodothyronine levels decrease by 50% or more during cardiopulmonary bypass. However, there is conflicting evidence that prophylactic perioperative thyroxine/triiodothyronine therapy is a useful inotropic adjunct in adult patients undergoing routine cardiac surgery and whilst some studies report improved haemodynamic parameters in the immediate post-bypass period there is no evidence that its use influences postoperative morbidity, mortality or length of stay in the elective patient. It may, however, have a role as rescue therapy in supporting some high risk cases during weaning from CPB or bridging to LVAD or transplant.

High versus low dose of initial thyroid hormone replacement for congenital hypothyroidism

Congenital hypothyroidism is a condition that affects infants from birth and results from a missing or abnormally developed thyroid gland, abnormal production of thyroid hormones or a failure of the pituitary gland to stimulate thyroid hormone production. It affects approximately 1 in 3000 to 4000 newborn infants and early diagnosis and treatment is very important to achieve a good outcome.Treatment of congenital hypothyroidism consists of a daily dose of thyroid hormone (thyroxine). However, the initial dose of thyroxine required to improve outcomes for infants with this condition is unclear and has been the subject of several studies. Some studies have suggested that when infants with congenital hypothyroidism are treated with a higher dose of thyroxine compared with the standard dose, this results in earlier normalisation of the their thyroid hormones and leads to better developmental outcome and intelligence.

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Summaries for consumers

High versus low dose of initial thyroid hormone replacement for congenital hypothyroidism

Congenital hypothyroidism is a condition that affects infants from birth and results from a missing or abnormally developed thyroid gland, abnormal production of thyroid hormones or a failure of the pituitary gland to stimulate thyroid hormone production. It affects approximately 1 in 3000 to 4000 newborn infants and early diagnosis and treatment is very important to achieve a good outcome.Treatment of congenital hypothyroidism consists of a daily dose of thyroid hormone (thyroxine). However, the initial dose of thyroxine required to improve outcomes for infants with this condition is unclear and has been the subject of several studies. Some studies have suggested that when infants with congenital hypothyroidism are treated with a higher dose of thyroxine compared with the standard dose, this results in earlier normalisation of the their thyroid hormones and leads to better developmental outcome and intelligence.

Antithyroid drug regimen for treating Graves' hyperthyroidism

People who have Graves' hyperthyroidism have thyroid glands which are releasing too much thyroid hormone. This can cause goitres (swelling in the neck around the thyroid gland), sweating, bowel or menstrual problems, and other, especially eye symptoms (ophthalmopathy). Treatments include anti‐thyroid drugs, surgery or radiation to reduce thyroid tissue. There are several choices to be made when considering the drug treatment of Graves' hyperthyroidism including the choice of drug, dose, duration of therapy, addition of thyroid hormone (thyroxine) and when to discontinue therapy. The antithyroid drugs which were used in the included randomised controlled trials (RCTs) comprised carbimazole, propylthiouracil and methimazole.

Postnatal thyroid hormones for respiratory distress syndrome in preterm infants

In preterm infants with breathing problems after birth, there is no evidence that thyroid hormone treatment given immediately after delivery reduces the severity of breathing difficulties or improves outcomes. Infants born prematurely are at risk of breathing problems due to lack of surfactant production by the lungs in the first days after birth. In animal research, thyroid hormones given before birth stimulate surfactant production and reduce the incidence and severity of breathing problems. This review found two small trials that compared the use of thyroid hormones to no treatment in infants with breathing problems in the first hours after birth. No benefit was found from use of these hormones on severity of breathing problems or complications that occurred as a result of these breathing problems. The effect on longer term development was not reported.

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