Thyroid Hormone Replacement Therapy

Dr. Frieze suggests educating patients on the importance of consistent therapy & precise dosing with Synthroid. There are certain foods that can interfere with the way SYNTHROID works, particularly we think about high-fiber foods that can interact with the absorption of thyroid medications. There are also certain vitamins and supplements that can interfere with the absorption of SYNTHROID. Mistaken generic users defined as those who reported taking SYNTHROID but did not have “SYNTHROID” embossed on the pill in a national online survey conducted in 2021 of 1908 adults diagnosed with hypothyroidism and currently taking LT4 products. A levothyroxine product that is not therapeutically equivalent with SYNTHROID might not have the exact same effect on the patient’s TSH as SYNTHROID.

SYNTHROID®(levothyroxine sodium tablets, USP)

• The estimated background risk of major birth defects and miscarriage for the indicated population is unknown.
• Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with levothyroxine sodium tablets see Contraindications (4).
• Therefore, SYNTHROID therapy should be initiated immediately upon diagnosis and is generally continued for life.

The recommended starting daily dosage of levothyroxine sodium tablets in pediatric patients with primary, secondary, or tertiary hypothyroidism is based on body weight and changes with age as described in Table 2. Titrate the dosage (every 2 weeks) as needed based on serum TSH or free-T4 until the patient is euthyroid see Dosage and Administration (2.2) . The recommended starting daily synthroid anorexia dosage of levothyroxine sodium tablets 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.

Specific Patient Populations

TSH may not normalize due to a resetting of the pituitary-thyroid feedback threshold as a result of in utero hypothyroidism. Careful inquiry should then be made regarding compliance, dose of medication administered, and method of administration prior to raising the dose of SYNTHROID. Furosemide has been shown to inhibit the protein binding of T4 to TBG and albumin, causing an increase free T4 fraction in serum. Furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower the total T4 level. Phenytoin and carbamazepine reduce serum protein binding of levothyroxine, and total and free T4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid.

• Addition of levothyroxine sodium tablets therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements.
• 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.
• Monitor serum free-T4 levels and maintain in the upper half of the normal range in these patients.
• Changes in TBG concentration must be considered when interpreting T4 and T3 values, which necessitates measurement and evaluation of unbound (free) hormone and/or determination of the free T4 index (FT4I).

SYNTHROID is administered as a single daily dose, preferably one-half to one-hour before breakfast. SYNTHROID should be taken at least 4 hours apart from drugs that are known to interfere with its absorption (see PRECAUTIONS – Drug Interactions). Inadequate levothyroxine dosage will produce or fail to ameliorate the signs and symptoms of hypothyroidism. Changes in TBG concentration must be considered when interpreting T4 and T3 values, which necessitates measurement and evaluation of unbound (free) hormone and/or determination of the free T4 index (FT4I). Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentrations. Decreases in TBG concentrations are observed in nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, and after androgen or corticosteroid therapy (see also Table 2).

Effects on Bone Mineral Density

SYNTHROID is indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Serum TSH levels should be monitored and the levothyroxine sodium tablets dosage adjusted during pregnancy. Since postpartum TSH levels are similar to preconception values, the levothyroxine sodium tablets dosage should return to the pre-pregnancy dose immediately after delivery see Dosage and Administration (2.3). Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. 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.

Many drugs affect thyroid hormone pharmacokinetics and metabolism (e.g., absorption, synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to SYNTHROID. In addition, thyroid hormones and thyroid status have varied effects on the pharmacokinetics and actions of other drugs. A listing of drug-thyroidal axis interactions is contained in Table 2. Concurrent use of sympathomimetics and SYNTHROID may increase the effects of sympathomimetics or thyroid hormone.

Label: SYNTHROID- levothyroxine sodium tablet

In the elderly and in patients with cardiovascular disease, SYNTHROID should be initiated at lower doses than those recommended in younger individuals or in patients without cardiac disease. Patients with coronary artery disease who are receiving SYNTHROID should be closely monitored for cardiac arrhythmias during surgical procedures. Closely monitor infants during the first 2 weeks of levothyroxine sodium tablets therapy for cardiac overload and arrhythmias.

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. Persistent clinical and laboratory evidence of hypothyroidism despite an apparent adequate replacement dose of SYNTHROID may be evidence of inadequate absorption, poor compliance, drug interactions, or a combination of these factors.

Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products. These include urticaria, pruritus, skin rash, flushing, angioedema, various GI symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness and wheezing. Since some more severely affected children may become clinically hypothyroid when treatment is discontinued for 30 days, an alternate approach is to reduce the replacement dose of levothyroxine by half during the 30-day trial period. If, after 30 days, the serum TSH is elevated above 20 mU/L, the diagnosis of permanent hypothyroidism is confirmed, and full replacement therapy should be resumed.

Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens, and corticosteroids decrease TBG concentration. Stop biotin and biotin-containing supplements for at least 2 days before assessing TSH and/or T4 levels see Drug Interactions (7.10). The SYNTHROID dosage is based on the target level of TSH suppression for the stage and clinical status of thyroid cancer.