Weight-Based Levothyroxine Dosage Adjustment for Hypothyroidism

The data that support the findings of this study are available from Optum Clinformatics® but restrictions apply to the availability of these data, which were used under license for the current study. The data used in this study are fully de-identified and HIPAA compliant. Given the retrospective nature of the study design and the de-identified data, the study was exempt from ethics board approval. All authors had full access to all of the data in this study and take complete responsibility for the integrity of the data and accuracy of the data analysis. The problem, the AACE and ATA state, becomes even greater if a patient switches between generics or between a generic and Synthroid.

Dosing And Administration

This medicine may increase your risk of heart rhythm problems or heart attack. Check with your doctor right away if you have dizziness, fainting, fast, slow, or irregular heartbeat, chest pain or discomfort, or pain or discomfort in the arms, jaw, back, or neck. Using this medicine with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco. Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur.

International Patients

The American Thyroid Association recommends taking the same brand-name (or generic) medication throughout your treatment. The association emphasizes that “thyroid disease often requires lifelong therapy and is best managed with consistent and precise treatment with the same (type) of thyroid hormone.” Your thyroid is a small, butterfly-shaped gland in the front of your neck. These hormones affect synthroid pills nearly every organ in your body and control many of your body’s most important functions. For example, they affect your breathing, heart rate, weight, digestion, and moods.

Levothyroxine injection is used to treat myxedema coma (severe hypothyroidism), a condition where the thyroid gland does not produce enough thyroid hormone. The powder form of levothyroxine injection can be used as a substitute for the oral dose when a rapid effect is needed and when the oral route is not allowed. Several studies have investigated the clinical efficacy of generic levothyroxine compared to Synthroid. Circulating thyroid hormones are greater than 99% bound to plasma proteins, including thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA), and albumin (TBA), whose capacities and affinities vary for each hormone. The higher affinity of both TBG and TBPA for T4 partially explains the higher serum levels, slower metabolic clearance, and longer half-life of T4 compared to T3.

• Since postpartum TSH levels are similar to preconception values, the SYNTHROID dosage should return to the pre-pregnancy dose immediately after delivery see DOSAGE AND ADMINISTRATION.
• For adult patients with primary hypothyroidism, titrate until the patient is clinically euthyroid and the serum TSH returns to normal see Recommended Dosage And Titration.
• Only mix the crushed tablets with water; do not mix it with food or soybean infant formula.
• Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentration.

Brand-name preparations are usually the first ones available on the market. After a period of time, other manufacturers are allowed to make generic versions of the same drug. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Women need more iodine when they are pregnant because the baby gets iodine from the mother’s diet.

Adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for SYNTHROID and any potential adverse effects on the breastfed infant from SYNTHROID or from the underlying maternal condition. Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism and may result in unpredictable absorption of levothyroxine sodium from the gastrointestinal tract.

Switchers were also more likely to have the composite clinical endpoint OR 1.23; CI (1.12–1.37) and to have individual diagnoses of chronic kidney disease, depression, fatigue, hypertension, or obesity in the post-period. A 2019 study published in Advances in Therapy compared 9,925 adults who consistently used Synthroid to 9,925 adults who switched from Synthroid to a generic. What the researchers found was that people who switched were 15% more likely to have their thyroid hormones fall out of the “normal” range than those who stuck with Synthroid. Levothyroxine sodium is the second-most prescribed drug in the United States, with approximately 25 million people using either Synthroid or generic levothyroxine to manage their hypothyroidism (low thyroid function).

References and abstracts from MEDLINE/PubMed (National Library of Medicine)

Monitor for cardiac arrhythmias during surgical procedures in patients with coronary artery disease receiving suppressive SYNTHROID therapy. Monitor patients receiving concomitant SYNTHROID and sympathomimetic agents for signs and symptoms of coronary insufficiency. SYNTHROID may reduce the therapeutic effects of digitalis glycosides. Serum digitalis glycoside levels may decrease when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides. Monitor serum free-T4 levels and maintain in the upper half of the normal range in these patients. Biotin supplementation may interfere with immunoassays for TSH, T4, and T3, resulting in erroneous thyroid hormone test results.

• Women need more iodine when they are pregnant because the baby gets iodine from the mother’s diet.
• And you have to be your own best advocate, working alongside a healthcare provider who will listen to you and guide you to the right solution.
• Because hypothyroidism develops slowly, many people don’t notice symptoms of the disease for months or even years.
• Protein-bound thyroid hormones exist in reverse equilibrium with small amounts of free hormone.

What is hypothyroidism?

If you notice any other effects, check with your healthcare professional. Appropriate studies performed to date have not demonstrated pediatrics-specific problems that would limit the usefulness of levothyroxine injection in the pediatric population. Ramon Espaillat and Maureen J. Lage participated in the data collection. All authors participated in the study design, analysis and interpretation of data, and writing, reviewing and approving the publication. Long-term carcinogenicity studies in animals to evaluate the carcinogenic potential of levothyroxine have not been performed.

Titrate the dosage (every 2 weeks) as needed based on serum TSH or free- T4 until the patient is euthyroid see Important Considerations For Dosing. Lean body mass is a better predictor of the dosage requirement than actual body weight.5 Without this clarification, some patients may receive a dosage of levothyroxine that is too high. According to El-Khoury, a major reason for inappropriate diagnoses is seasonal variation. This is also when more people may experience symptoms of seasonal affective disorder (SAD), which can have symptoms similar to hypothyroidism. Because current screening measures do not consider the natural variation, many patients presenting with hypothyroidism-like symptoms are getting tested at a time when their TSH levels are naturally higher and being prescribed levothyroxine.