Furthermore, it is available as both brand-name and generic products. While the FDA approved the use of generic levothyroxine for brand-name levothyroxine in 2004, the decision was met with disagreement by several medical associations. The American Association of Clinical Endocrinologists (AACE), the Endocrine Society, and the American Thyroid Association did not agree with the FDA that brand-name and generic formulations of levothyroxine were bioequivalent. As such,  people were recommended to be started and kept on either brand-name or generic levothyroxine formulations and not changed back and forth from one to the other. For people who do switch products,  their TSH and free T4 levels should be tested after six weeks to check that they are within normal range.Common brand names include Eltroxin, Euthyrox, Eutirox, Letrox, Levaxin, Lévothyrox, Levoxyl, L-thyroxine, Thyrax, and Thyrax Duotab in Europe; Thyrox and Thyronorm in South Asia; Unithroid, Eutirox, Synthroid, and Tirosint in North and South America; and Thyrin and Thyrolar in Bangladesh. Numerous generic versions also are available.The related drug dextrothyroxine (D-thyroxine) was used in the past as a treatment for hypercholesterolemia (elevated cholesterol levels), but was withdrawn due to cardiac side effects. Once weekly thyroxine (OWT) preparations are also available for clinical use. A recent meta-analysis published by Dutta et al. involving data from 4 studies (294 patients) showed that OWT is associated with less efficient control of hypothyroidism, risks of supraphysiologic elevation of thyroid hormone levels along with transient echocardiographic changes in some patients following 2-4 h of thyroxine intake.
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, body mass index, 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 about 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 study in 2015 showed greater efficacy of levothyroxine when taken at bedtime. Doses of levothyroxine that normalize serum TSH may not normalize abnormal levels of LDL cholesterol and total cholesterol.Poor compliance in taking the medicine is the most common cause of elevated TSH levels in people receiving appropriate doses of levothyroxine. 50 and older
For older people (over 50 years old) and people with known or suspected ischemic heart disease, levothyroxine therapy should not be initiated at the full replacement dose. Since thyroid hormone increases the hearts oxygen demand by increasing heart rate and contractility, starting at higher doses may cause an acute coronary syndrome or an abnormal heart rhythm. Pregnancy and breastfeeding
Hypothyroidism is common among pregnant women. A nationwide cohort study showed that 1.39% of all pregnant women in 2010 in Denmark received a prescription of levothyroxine during pregnancy.