Synthroid Levothyroxine Sodium: Side Effects, Uses, Dosage, Interactions, Warnings

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). Levothyroxine is generally continued for life in these patients see WARNINGS AND PRECAUTIONS. Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with SYNTHROID see CONTRAINDICATIONS.

More about levothyroxine

Closely monitor coagulation tests to permit appropriate and timely dosage adjustments. These include urticaria, pruritus, skin rash, flushing, angioedema, various gastrointestinal symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness, and wheezing. 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. Therapy is usually instituted using low doses, with increments which depend on the cardiovascular status of the patient. The usual starting dose is 30 mg RenThyroid (Thyroid Tablets, USP), with increments of 15 mg every 2 to 3 weeks. A lower starting dosage, 15 mg/day, is recommended in patients with long-standing myxedema, particularly if cardiovascular impairment is suspected, in which case extreme caution is recommended.

Administration of sertraline in patients stabilized on SYNTHROID may result in increased SYNTHROID requirements. Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in pediatric patients receiving levothyroxine therapy. SYNTHROID is 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. For adult patients with primary hypothyroidism, titrate until the patient is clinically euthyroid and the serum TSH returns to normal. Exogenous thyroid hormone may produce regression of metastases from follicular and papillary carcinoma of the thyroid and is used as ancillary therapy of these conditions with radioactive iodine. Therefore, larger amounts of thyroid hormone than those used for replacement therapy are required.

Oral Anticoagulants

Levoxyl treats hypothyroidism (low thyroid hormone) and treats or prevents goiter. Tirosint is used for hashimoto’s disease, hypothyroidism, after thyroid removal, myxedema coma … The diagnosis of hypothyroidism is confirmed by measuring TSH levels using a sensitive assay (second generation assay sensitivity ≤ 0.1 mIU/L or third generation assay sensitivity ≤ 0.01 mIU/L) and measurement of free-T4. SYNTHROID is contraindicated in patients with uncorrected adrenal insufficiency see Warnings and Precautions (5.4). You are encouraged to report negative side effects of prescription drugs to the FDA. SYNTHROID is contraindicated in patients with uncorrected adrenal insufficiency see WARNINGS AND PRECAUTIONS.

Medullary carcinoma of the thyroid is usually unresponsive to this therapy. Failure to respond to doses of 180 mg suggests lack of compliance or malabsorption. Maintenance dosages 60 to 120 mg/day usually result in normal serum T4 and T3 levels. The dosage of thyroid hormones is determined by the indication and must in every case be individualized according to patient response and laboratory findings. In general, levothyroxine therapy should be instituted at full replacement doses as soon as possible.

• Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (rT3).
• Levothyroxine sodium (T4) is given at a starting dose of 400 mcg (100 mcg/mL) given rapidly, and is usually well tolerated, even in the elderly.
• Monitor patients receiving concomitant SYNTHROID and sympathomimetic agents for signs and symptoms of coronary insufficiency.
• The protein anabolic effects of thyroid hormones are essential to normal growth and development.

Overtreatment with levothyroxine sodium may have adverse cardiovascular effects such as an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias. Concomitant administration of levothyroxine and sympathomimetic agents to patients with coronary artery disease may precipitate coronary insufficiency. The recommended starting daily dosage of SYNTHROID 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 dosage of SYNTHROID in adults with primary, secondary, or tertiary hypothyroidism is based on age and comorbid cardiac conditions, as described in Table 1.

4 Monitoring TSH and/or Thyroxine (T Levels

In a medical setting, you are not likely to miss a dose of levothyroxine injection. You should not use levothyroxine if you are allergic to glycerin or edetate disodium, or if you have an untreated or uncontrolled adrenal gland disorder. Taking more than your recommended dose will not make this medicine synthroid nightmares more effective, and may cause serious side effects.

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. Protein-bound thyroid hormones exist in reverse equilibrium with small amounts of free hormone. Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins (see PRECAUTIONS – Drug Interactions and Drug-Laboratory Test Interactions). Thyroid hormones do not readily cross the placental barrier (see PRECAUTIONS – Pregnancy). Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins see Drug Interactions (7).

Thyroid hormone synthesis and secretion is regulated by the hypothalamic-pituitary-thyroid axis. Thyrotropin-releasing hormone (TRH) released from the hypothalamus stimulates secretion of thyrotropin-stimulating hormone, TSH, from the anterior pituitary. TSH, in turn, is the physiologic stimulus for the synthesis and secretion of thyroid hormones, L-thyroxine (T4) and L-triiodothyronine (T3), by the thyroid gland. Circulating serum T3 and T4 levels exert a feedback effect on both TRH and TSH secretion. When serum T3 and T4 levels increase, TRH and TSH secretion decrease.

Myxedema coma is usually precipitated in the hypothyroid patient of long-standing by intercurrent illness or drugs such as sedatives and anesthetics and should be considered a medical emergency. Therapy should be directed at the correction of electrolyte disturbances and possible infection besides the administration of thyroid hormones. Levothyroxine (T4) and liothyronine (T3) may be administered via a nasogastric tube but the preferred route of administration of both hormones is intravenous. Levothyroxine sodium (T4) is given at a starting dose of 400 mcg (100 mcg/mL) given rapidly, and is usually well tolerated, even in the elderly.

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