Levothyrox

Levothyroxine, also known as L-thyroxine, is a manufactured form of the thyroid hormone thyroxine (T4). It is used to treat thyroid hormone deficiency, including the severe form known as myxedema coma. It may also be used to treat and prevent certain types of thyroid tumors. It is not indicated for weight loss. Levothyroxine is taken by mouth or given by injection into a vein. Maximum effect from a specific dose can take up to six weeks to occur. Side effects from excessive doses include weight loss, trouble tolerating heat, sweating, anxiety, trouble sleeping, tremor, and fast heart rate. Use is not recommended in people who have had a recent heart attack. Use during pregnancy has been found to be safe. It is recommended that dosing be based on regular measurements of thyroid-stimulating hormone (TSH) and T4 levels in the blood. Much of the effect of levothyroxine is following its conversion to triiodothyronine (T3). Levothyroxine was first made in 1927. It is on the World Health Organization's List of Essential Medicines, which lists the most effective and safe medicines needed in a health system. Levothyroxine is available as a generic medication. The wholesale cost in the developing world is about US$0.58 to US$12.28 per month. In the United States, a typical month of treatment costs less than US$25. Levothyroxine was the most commonly prescribed medication in the United States as of 2016, with more than 114 million prescriptions. Levothyroxine is typically used to treat hypothyroidism, and is the treatment of choice for people with hypothyroidism, who often require lifelong thyroid hormone therapy. Doses of levothyroxine that normalize serum TSH may not normalize LDL cholesterol and total cholesterol. It may also be used to treat goiter via its ability to lower thyroid-stimulating hormone (TSH), a hormone that is considered goiter-inducing. Levothyroxine is also used as interventional therapy in people with nodular thyroid disease or thyroid cancer to suppress thyroid-stimulating hormone (TSH) secretion. A subset of people with hypothyroidism treated with an appropriate dose of levothyroxine will describe continuing symptoms despite TSH levels in the normal range. In these people, further laboratory and clinical evaluation is warranted as they may have another cause for their symptoms. Furthermore, it is important to review their medications and possible dietary supplements as several medications can affect thyroid hormone levels. Levothyroxine is also used to treat subclinical hypothyroidism which is defined by an elevated TSH level and a normal-range free T4 level without symptoms. Such people may be asymptomatic and whether they should be treated is controversial. One benefit of treating this population with levothyroxine therapy is preventing development of hypothyroidism. As such, it is recommended that treatment should be taken into account for patients with initial TSH levels > 10 mIU/L, people with elevated thyroid peroxidase antibody titers, people with symptoms of hypothyroidism and TSH levels between 5–10 mIU/L, and women who are pregnant or want to become pregnant. Oral dosing for patients with subclinical hypothyroidism is 1 µg/kg/day. It is also used to treat myxedema coma, which is a severe form of hypothyroidism characterized by mental status changes and hypothermia. As it is a medical emergency with a high mortality rate, it should be treated in the intensive care unit with thyroid hormone replacement and aggressive management of individual organ system complications. Dosages vary according to the age groups and the individual condition of the person, body weight and compliance to the medication and diet. Other predictors of the required dosage are sex, BMI, deiodinase activity (SPINA-GD) and etiology of hypothyroidism. Annual or semiannual clinical evaluations and TSH monitoring are appropriate after dosing has been established. Levothyroxine is taken on an empty stomach approximately half an hour to an hour before meals. As such, thyroid replacement therapy is usually taken 30 minutes prior to eating in the morning. For patients with trouble taking levothyroxine in the morning, bedtime dosing is effective as well. A recent study published in JAMA showed greater efficacy of levothyroxine when taken at bedtime.