Synthroid

— THERAPEUTIC CATEGORIES —
  • Pancreatic, thyroid, and other endocrine cancers
  • Thyroid disease
PAGE CONTENTS
  • Jump to Section
  • Generic Name & Formulations
  • Indications
  • Dosage and Administration
  • Contraindications
  • Boxed Warnings
  • Warnings/Precautions
  • Pharmacokinetics
  • Interactions
  • Adverse Reactions
  • Clinical Trials
  • Note
  • Patient Counseling

    • Synthroid Generic Name & Formulations

    Legal Class

    Rx

    General Description

    Levothyroxine sodium 25mcg, 50mcg (dye-free), 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg; scored tabs.

    Pharmacological Class

    T4 (synthetic).

    See Also

      How Supplied

      Tabs (all)—90, 1000; Tabs (50mcg, 75mcg, 100mcg, 125mcg, 150mcg, 200mcg)—100; Single-use vials—contact supplier

      Manufacturer

      AbbVie

      Generic Availability

      YES

      Mechanism of Action

      Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

      Synthroid Indications

      Indications

      As adjunct to surgery and radioiodine therapy for thyrotropin-dependent well-differentiated thyroid cancer.

      Limitations of Use

      Not for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients. Not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

      Synthroid Dosage and Administration

      Adult

      Take in AM on empty stomach, ½ to 1hr before breakfast. May crush tabs and mix in 5–10mL water. Individualize. >2mcg/kg per day. High-risk tumors: see full labeling.

      Children

      Not established.

      Synthroid Contraindications

      Contraindications

      Uncorrected adrenal insufficiency.

      Synthroid Boxed Warnings

      Boxed Warning

      Not for treatment of obesity or for weight loss.

      Synthroid Warnings/Precautions

      Warnings/Precautions

      Underlying cardiovascular disease. Monitor for cardiac arrhythmias during surgery in those with coronary artery disease. Reduce or withhold dose for 1 week if cardiac symptoms develop or worsen; restart at lower dose. Myxedema coma: use IV levothyroxine. Adults: Monitor TSH 6–8 weeks after dose change then every 6–12 months when stable. Peds: Monitor TSH and total or free-T4 at 2 and 4 weeks after initiation, 2 weeks after dose change then every 3–12 months thereafter. Correct adrenal insufficiency before initiation. Diabetes; monitor glycemic control. Increased bone resorption and decreased BMD (esp. in post-menopausal women). Use lowest effective dose. Elderly. Pregnancy: monitor TSH/free-T4 at least every trimester; adjust dose and do not discontinue (see full labeling). Nursing mothers.

      Synthroid Pharmacokinetics

      Absorption

      Relative bioavailability of Synthroid tablets vs an equal nominal dose of oral levothyroxine sodium solution is ~93%.

      Distribution

      Plasma protein bound: >99%.

      Metabolism

      Hepatic. 

      Elimination

      Renal (major), fecal (~20%). Half-life: 6–7 days (T4), ≤2 days (T3).

      Synthroid Interactions

      Interactions

      See full labeling. Absorption reduced by some foods (eg, soy flour, cottonseed meal, walnuts, fiber, grapefruit juice), aluminum and magnesium hydroxide, simethicone, proton pump inhibitors, iron, sucralfate; monitor. Give at least 4hrs apart from calcium carbonate, ferrous sulfate, sevelamer, lanthanum, bile acid sequestrants (eg, colesevelam, cholestyramine, colestipol), ion exchange resins (eg, kayexalate). Thyroid levels may be affected by clofibrate, estrogens, heroin, methadone, 5-fluorouracil, mitotane, tamoxifen, androgens, anabolic steroids, asparaginase, glucocorticoids, nicotinic acid (slow-release), salicylates (>2g/day), β-blockers (eg, propranolol), glucocorticoids, amiodarone. Monitor thyroid parameters with concomitant carbamazepine, furosemide (>80mg IV), heparin, hydantoins, NSAIDs. Potentiates, and is potentiated by, tri- and tetracyclic antidepressants. Concomitant sympathomimetics; monitor for coronary insufficiency. Antagonized by phenobarbital, rifampin, sertraline. Antagonizes digitalis glycosides. Marked hypertension and tachycardia with ketamine. Hypothyroidism risk with concomitant tyrosine kinase inhibitors (eg, imatinib). Monitor with oral anticoagulants, antidiabetic agents, orlistat. Concomitant biotin or biotin-containing supplements may interfere with thyroid hormone immunoassays; discontinue supplements for at least 2 days prior to thyroid testing.

      Synthroid Adverse Reactions

      Adverse Reactions

      Arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, skin rash; seizures (rare); Children: pseudotumor cerebri, slipped capital femoral epiphysis.

      Synthroid Clinical Trials

      See Literature

      Synthroid Note

      Not Applicable

      Synthroid Patient Counseling

      See Literature

      Synthroid Generic Name & Formulations

      Legal Class

      Rx

      General Description

      Levothyroxine sodium 25mcg, 50mcg (dye-free), 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg; scored tabs.

      Pharmacological Class

      T4 (synthetic).

      See Also

      How Supplied

      Tabs (all)—90, 1000; Tabs (50mcg, 75mcg, 100mcg, 125mcg, 150mcg, 200mcg)—100; Single-use vials—contact supplier

      Manufacturer

      AbbVie

      Generic Availability

      YES

      Mechanism of Action

      Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

      Synthroid Indications

      Indications

      Hypothyroidism.

      Limitations of Use

      Not for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients. Not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

      Synthroid Dosage and Administration

      Adult

      Take in AM on empty stomach, ½ to 1hr before breakfast. Individualize. Primary hypothyroidism: 1.6mcg/kg once daily; titrate in increments of 12.5–25mcg every 4–6 weeks until euthyroid and serum TSH normalized. Elderly or underlying cardiovascular disease: initially 12.5–25mcg once daily; titrate every 6–8 weeks until euthyroid and serum TSH normalized. Usual max 200mcg/day. Severe hypothyroidism: initially 12.5–25mcg once daily; titrate in increments of 12.5–25mcg every 2–4 weeks until euthyroid and serum TSH normalized. Secondary or tertiary hypothyroidism: see full labeling.

      Children

      Take in AM on empty stomach, ½ to 1hr before breakfast. May crush tabs and mix in 5–10mL water. Congenital or acquired hypothyroidism: 0–3months: 10–15mcg/kg per day; 3–6months: 8–10mcg/kg per day; 6–12months: 6–8mcg/kg per day; 1–5yrs: 5–6mcg/kg per day; 6–12yrs: 4–5mcg/kg per day; >12yrs but growth and puberty incomplete: 2–3mcg/kg per day; growth and puberty complete: as adult. Newborns at risk for cardiac failure: initiate at lower dose; increase dose every 4–6 weeks as needed. Risk for hyperactivity: initially ¼ full replacement dose; increase by ¼ dose weekly until full dose reached.

      Synthroid Contraindications

      Contraindications

      Uncorrected adrenal insufficiency.

      Synthroid Boxed Warnings

      Boxed Warning

      Not for treatment of obesity or for weight loss.

      Synthroid Warnings/Precautions

      Warnings/Precautions

      Underlying cardiovascular disease. Monitor for cardiac arrhythmias during surgery in those with coronary artery disease. Reduce or withhold dose for 1 week if cardiac symptoms develop or worsen; restart at lower dose. Myxedema coma: use IV levothyroxine. Adults: Monitor TSH 6–8 weeks after dose change then every 6–12 months when stable. Peds: Monitor TSH and total or free-T4 at 2 and 4 weeks after initiation, 2 weeks after dose change then every 3–12 months thereafter. Correct adrenal insufficiency before initiation. Diabetes; monitor glycemic control. Increased bone resorption and decreased BMD (esp. in post-menopausal women). Use lowest effective dose. Elderly. Pregnancy: monitor TSH/free-T4 at least every trimester; adjust dose and do not discontinue (see full labeling). Nursing mothers.

      Synthroid Pharmacokinetics

      Absorption

      Relative bioavailability of Synthroid tablets vs an equal nominal dose of oral levothyroxine sodium solution is ~93%.

      Distribution

      Plasma protein bound: >99%.

      Metabolism

      Hepatic. 

      Elimination

      Renal (major), fecal (~20%). Half-life: 6–7 days (T4), ≤2 days (T3).

      Synthroid Interactions

      Interactions

      See full labeling. Absorption reduced by some foods (eg, soy flour, cottonseed meal, walnuts, fiber, grapefruit juice), aluminum and magnesium hydroxide, simethicone, proton pump inhibitors, iron, sucralfate; monitor. Give at least 4hrs apart from calcium carbonate, ferrous sulfate, sevelamer, lanthanum, bile acid sequestrants (eg, colesevelam, cholestyramine, colestipol), ion exchange resins (eg, kayexalate). Thyroid levels may be affected by clofibrate, estrogens, heroin, methadone, 5-fluorouracil, mitotane, tamoxifen, androgens, anabolic steroids, asparaginase, glucocorticoids, nicotinic acid (slow-release), salicylates (>2g/day), β-blockers (eg, propranolol), glucocorticoids, amiodarone. Monitor thyroid parameters with concomitant carbamazepine, furosemide (>80mg IV), heparin, hydantoins, NSAIDs. Potentiates, and is potentiated by, tri- and tetracyclic antidepressants. Concomitant sympathomimetics; monitor for coronary insufficiency. Antagonized by phenobarbital, rifampin, sertraline. Antagonizes digitalis glycosides. Marked hypertension and tachycardia with ketamine. Hypothyroidism risk with concomitant tyrosine kinase inhibitors (eg, imatinib). Monitor with oral anticoagulants, antidiabetic agents, orlistat. Concomitant biotin or biotin-containing supplements may interfere with thyroid hormone immunoassays; discontinue supplements for at least 2 days prior to thyroid testing.

      Synthroid Adverse Reactions

      Adverse Reactions

      Arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, skin rash; seizures (rare); Children: pseudotumor cerebri, slipped capital femoral epiphysis.

      Synthroid Clinical Trials

      See Literature

      Synthroid Note

      Not Applicable

      Synthroid Patient Counseling

      See Literature

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