What is the use of Euthyrox (levothyroxine)?

From the Guidelines

Euthyrox (levothyroxine) is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone, with the goal of reducing morbidity and mortality while improving quality of life. According to the study published in the Annals of Internal Medicine 1, levothyroxine therapy is a synthetic preparation of a natural hormone found in the body, and treatment of hypothyroidism with levothyroxine generally lasts for many years.

Key Considerations for Use

• The dosing of Euthyrox is highly individualized, usually starting at 25-50 mcg daily for adults with mild hypothyroidism, and adjusted based on thyroid function tests every 6-8 weeks until optimal levels are achieved, as indicated by the need to avoid overtreatment which can lead to adverse effects such as osteoporosis, fractures, abnormal cardiac output, or ventricular hypertrophy 1.
• Maintenance doses typically range from 100-200 mcg daily, and it is crucial to take Euthyrox consistently at the same time each day to maintain stable hormone levels.
• Patients should be aware that certain medications, supplements (especially calcium, iron), and foods can interfere with absorption, so timing of these should be separated from Euthyrox intake by at least 4 hours.
• Regular monitoring of thyroid function is essential to ensure proper dosing and minimize the risk of long-term adverse effects, as the ultimate effect of long-term overdosing with levothyroxine is unknown but could increase risk for several health issues 1.

Clinical Implications

• The use of Euthyrox should be guided by the principle of minimizing harm, given that overtreatment may lead to iatrogenic hypothyroidism and dependency on lifelong thyroid hormone therapy, especially in cases of asymptomatic hyperthyroidism 1.
• Clinicians should consider the potential for opportunity costs when treating thyroid dysfunction, ensuring that the focus on thyroid health does not detract from other important health needs of the patient.
• The lack of direct evidence on the benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults underscores the need for careful consideration and individualized decision-making in the use of Euthyrox 1.

From the FDA Drug Label

Levothyroxine sodium tablets are a L-thyroxine (T4) indicated in adult and pediatric patients, including neonates, for: • Hypothyroidism: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. • Pituitary Thyrotropin (Thyroid‑Stimulating Hormone, TSH) Suppression: As an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.

The use of Euthyrox (levothyroxine) is for:

• Hypothyroidism: as replacement therapy in primary, secondary, and tertiary congenital or acquired hypothyroidism
• Pituitary Thyrotropin (Thyroid-Stimulating Hormone, TSH) Suppression: as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer 2

From the Research

Use of Euthyrox (Levothyroxine)

The use of Euthyrox, also known as levothyroxine, is primarily for the treatment of hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones.

• Levothyroxine is used as replacement therapy to normalize the serum thyroid-stimulating hormone (TSH) concentration 3.
• It is also used to suppress the serum TSH concentration in certain conditions, such as benign solitary nonfunctioning thyroid nodules and thyroid cancer 3.
• The goal of levothyroxine therapy is to normalize the serum TSH level, which is usually achieved with a full replacement dosage of 1.6 micrograms/kg body weight per day 3.
• Levothyroxine therapy is usually started at a dose of about 1.5 microg/kg per day in young adults, while elderly patients and those with coronary artery disease should start at a lower dose of 12.5 to 50 microg per day 4.

Administration and Monitoring

• Levothyroxine can be administered in various forms, including tablets, liquid solutions, and soft gel capsules 5.
• The liquid solution and soft gel capsule formulations have been shown to have a more rapid absorption and can overcome interactions with foods, drugs, or malabsorptive conditions that can impair tablet absorption 5.
• Treatment monitoring is based mainly on blood TSH assay, and dose adjustment should only be considered after 6 to 12 weeks, given the long half-life of levothyroxine 4.
• Certain drugs, such as iron and calcium, can reduce the gastrointestinal absorption of levothyroxine, while enzyme inducers can reduce its efficacy 4.

Therapeutic Challenges

• Normalizing serum TSH levels by lifelong treatment with levothyroxine remains the primary goal of therapy for patients with hypothyroidism 6.
• However, some patients may be complex to manage, and bringing serum TSH to within its reference range does not always resolve their symptoms of hypothyroidism 6.
• Weekly levothyroxine replacement may be a suitable alternative to daily replacement for non-adherent patients, but larger randomized trials with longer duration of follow-up are needed to firmly establish its role 7.