Synthroid: Package Insert Prescribing Information
Grapefruit juice may delay the absorption of levothyroxine and reduce its bioavailability. Titrate the dose of SYNTHROID carefully and monitor response to titration to avoid these effects see Dosage and Administration (2.4). Consider the potential for food or drug interactions and adjust the administration or dosage of SYNTHROID as needed see Dosage and Administration (2.1), Drug Interactions (7.1), and Clinical Pharmacology (12.3). Biotin supplementation may interfere with immunoassays for TSH, T4, and T3, resulting in erroneous thyroid hormone test results. Stop biotin and biotin-containing supplements for at least 2 days before assessing TSH and/or T4 levels see Drug Interactions (7.10).
SYNTHROID® (levothyroxine sodium) tablets, for oral use is a prescription, man-made thyroid hormone that is used to treat a condition called hypothyroidism in adults and children, including infants. It is meant to replace a hormone that is usually made by your thyroid gland. Generally, thyroid replacement treatment is to be taken for life. SYNTHROID should not be used to treat noncancerous growths or enlargement of the thyroid in patients with normal iodine levels, or in cases of temporary hypothyroidism caused by inflammation of the thyroid gland (thyroiditis). The recommended starting daily dosage of SYNTHROID in adults with primary, secondary, or tertiary hypothyroidism is based on age and comorbid cardiac conditions, as described in Table 1. For patients at risk of atrial fibrillation or patients with underlying cardiac disease, start with a lower dosage and titrate the dosage more slowly to avoid exacerbation of cardiac symptoms.
Acute Adrenal Crisis In Patients With Concomitant Adrenal Insufficiency
Initiate SYNTHROID therapy in this population at lower doses than those recommended in younger individuals or in patients without cardiac disease see Dosage and Administration (2.3) and Use in Specific Populations (8.5). For adult patients with primary hypothyroidism, titrate until the patient is clinically euthyroid and the serum TSH returns to normal see Dosage and Administration (2.3). Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins see DRUG INTERACTIONS.
Providing a complete list of medications to the doctor will help with getting the correct dose established for each individual patient. Do not store the crushed tablet/water mixture and do not administer it mixed with foods that decrease absorption of levothyroxine, such as soybean-based infant formula. Synthroid should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants. Inquire whether patients are taking biotin or biotin-containing supplements. If so, advise them to stop biotin supplementation at least 2 days before assessing TSH and/or T4 levels see Dosage and Administration (2.4) and Drug Interactions (7.10).
- Be sure to let your doctor know if there are any changes to your diet or to the medications you take.
- This document does not contain all possible side effects and others may occur.
- Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%.
- Do not store the crushed tablet/water mixture and do not administer it mixed with foods that decrease absorption of levothyroxine, such as soybean-based infant formula.
- Serum TSH levels should be monitored and the SYNTHROID dosage adjusted during pregnancy.
Drugs Known To Affect Thyroid Hormone Pharmacokinetics
- With hypothyroidism, the thyroid is unable to produce enough thyroid hormone.
- The better you understand hypothyroidism, the better prepared you are to manage it.
- Synthroid is also used in patients who need surgery and radioiodine therapy to manage a type of thyroid cancer called well-differentiated thyroid cancer.
- SYNTHROID is not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
Certain other medicines may also increase or decrease the effects of Synthroid. Addition of SYNTHROID therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control, especially when thyroid therapy is started, changed, or discontinued see Warnings and Precautions (5.5). Thyroid hormone increases metabolic clearance of glucocorticoids. Initiation of thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate an acute adrenal crisis in patients with adrenal insufficiency. Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with SYNTHROID see Contraindications (4).
More about Synthroid (levothyroxine)
The liver is the major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including the kidney and other tissues. Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (rT3). Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation. The signs and symptoms of overdosage are those of hyperthyroidism see WARNINGS AND PRECAUTIONS and Adverse Reactions. Seizures occurred in a 3-yearold child ingesting 3.6 mg of levothyroxine.
Foods containing soy and cottonseed meal can make Synthroid less effective. Walnuts, grapefruit juice, and dietary fiber can also make Synthroid less effective. If you eat any of these on a regular basis, check with your doctor. Enter medications to view a detailed interaction report using our Drug Interaction Checker.
Serum digitalis glycoside levels may decrease when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides. Stop biotin and biotin-containing supplements for at least 2 days before assessing TSH and/or T4 levels see DRUG INTERACTIONS. The signs and symptoms of overdosage are those of hyperthyroidism see Warnings and Precautions (5) and Adverse Reactions (6). Seizures occurred in a 3-year-old child ingesting 3.6 mg of levothyroxine. Symptoms may not necessarily be evident or may not appear until several days after ingestion of levothyroxine sodium. Serum TSH levels should be monitored and the SYNTHROID dosage adjusted during pregnancy.
Evaluate the need for dosage adjustments when regularly administering within one hour of certain foods that may affect SYNTHROID absorption. Oral levothyroxine sodium is a synthetic T4 hormone that exerts the same physiologic effect as hydrocodone synthroid endogenous T4, thereby maintaining normal T4 levels when a deficiency is present. Monitor for cardiac arrhythmias during surgical procedures in patients with coronary artery disease receiving suppressive SYNTHROID therapy.
In addition, many drugs and foods affect T4 absorption see Drug Interactions (7). In addition, many drugs and foods affect T4 absorption see DRUG INTERACTIONS. For secondary or tertiary hypothyroidism, serum TSH is not a reliable measure of SYNTHROID dosage adequacy and should not be used to monitor therapy.
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