Thyroid Hormone Replacement Therapy

Monitor patients receiving concomitant SYNTHROID and sympathomimetic agents for signs and symptoms of coronary insufficiency. The recommended daily dosage of SYNTHROID in pregnant patients is described in Table 3. Synthroid is a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body’s energy and metabolism. Biotin supplementation is known to interfere with synthroid route thyroid hormone immunoassays that are based on a biotin and streptavidin interaction, which may result in erroneous thyroid hormone test results. Stop biotin and biotin-containing supplements for at least 2 days prior to thyroid testing.

Dr. Frieze suggests educating patients on the importance of consistent therapy & precise dosing with Synthroid. You are encouraged to report negative side effects of prescription drugs to the FDA. If cardiac symptoms develop or worsen, reduce the SYNTHROID dose or withhold for one week and restart at a lower dose. Seizures have been reported rarely with the institution of levothyroxine therapy. In order for Synthroid to be effective, it should always be taken the same way every day. This is important because the amount of medicine you need is very precise.

Drug Interactions

• Because some preparations of the drug may contain iodine or lactose, patients should tell their doctors about such allergies or reactions to these components.
• Biotin supplementation is known to interfere with thyroid hormone immunoassays that are based on a biotin and streptavidin interaction, which may result in erroneous thyroid hormone test results.
• Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens, and corticosteroids decrease TBG concentration.
• TSH may not normalize in some patients due to in utero hypothyroidism causing a resetting of pituitary-thyroid feedback.
• This includes prescription and over-the-counter medicines, vitamins, and herbal products.
• Consumption of certain foods may affect SYNTHROID absorption thereby necessitating adjustments in dosing see DOSAGE AND ADMINISTRATION.

This is not a complete list of side effects and others may occur. We anticipate reposting the images once we are able identify and filter out images that do not match the information provided in the drug labels. Note that this list is not all-inclusive and includes only common medications that may interact with Synthroid. You should refer to the prescribing information for Synthroid for a complete list of interactions. Pregnant and lactating females need to discuss the dose and use of this medication with their caregivers. This document does not contain all possible side effects and others may occur.

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In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. In patients on a stable and appropriate replacement dosage, evaluate clinical and biochemical response every 6 to 12 months and whenever there is a change in the patient’s clinical status. Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%. The majority of the SYNTHROID dose is absorbed from the jejunum and upper ileum. The relative bioavailability of SYNTHROID tablets, compared to an equal nominal dose of oral levothyroxine sodium solution, is approximately 93%. T4 absorption is increased by fasting, and decreased in malabsorption syndromes and by certain foods such as soybeans.

• 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.
• You are encouraged to report negative side effects of prescription drugs to the FDA.
• The pituitary gland sends out TSH, which tells the thyroid to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
• 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).

Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens, and corticosteroids decrease TBG concentration. Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000. Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism. Monitor serum free-T4 levels and maintain in the upper half of the normal range in these patients. Patients The SYNTHROID dosage is based on the target level of TSH suppression for the stage and clinical status of thyroid cancer.

Because of the increased prevalence of cardiovascular disease among the elderly, initiate SYNTHROID at less than the full replacement dose see Dosage and Administration (2.3) and Warnings and Precautions (5.2). Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly. For adult patients with primary hypothyroidism, titrate until the patient is clinically euthyroid and the serum TSH returns to normal. 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 and Use In Specific Populations. Rapid restoration of normal serum T4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on cognitive development as well as on overall physical growth and maturation.

Use the serum free-T4 level to titrate SYNTHROID dosing until the patient is clinically euthyroid and the serum free-T4 level is restored to the upper half of the normal range see Dosage and Administration (2.3). Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects. Use the serum free-T4 level to titrate SYNTHROID dosing until the patient is clinically euthyroid and the serum free-T4 level is restored to the upper half of the normal range.

Published studies report that levothyroxine is present in human milk following the administration of oral levothyroxine. No adverse effects on the breastfed infant have been reported and there is no information on the effects of levothyroxine on milk production. Adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply. Concurrent use of sympathomimetics and SYNTHROID may increase the effects of sympathomimetics or thyroid hormone.

SYNTHROID is contraindicated in patients with uncorrected adrenal insufficiency see WARNINGS AND PRECAUTIONS. Long-term carcinogenicity studies in animals to evaluate the carcinogenic potential of levothyroxine have not been performed. Studies to evaluate mutagenic potential and animal fertility have not been performed. Concurrent use of ketamine and SYNTHROID may produce marked hypertension and tachycardia.

• Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000.
• Dr. Frieze suggests educating patients on the importance of consistent therapy & precise dosing with Synthroid.
• Stop biotin and biotin-containing supplements for at least 2 days before assessing TSH and/or T4 levels see DRUG INTERACTIONS.
• Enter medications to view a detailed interaction report using our Drug Interaction Checker.

Label: SYNTHROID- levothyroxine sodium tablet

TSH lower limit of quantification was 0.2 mIU/L and upper limit of normal was 5.6 mIU/L, as indicated by the shaded area. SYNTHROID is not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis. Administer SYNTHROID at least 4 hours before or after drugs known to interfere with SYNTHROID absorption. A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces.