Levothyroxine

Levothyroxine Brand Names

Estre | Euthyrox | Levo-T | Levothroid | Levoxyl | Synthroid | Thyro-Tabs | Tirosint | TIROSINT-SOL | Unithroid

What is Levothyroxine

Levothyroxine (T4) is an oral and parenteral synthetically derived levorotatory isomer of thyroxine (T4), a hormone secreted by the thyroid gland.

Levothyroxine products are preferred over naturally-derived thyroid hormones from animal glands; effects during dosage titration are more predictable due to the standardized hormonal content of levothyroxine products.

Oral levothyroxine is used in the treatment of primary, secondary (pituitary), and tertiary (hypothalamic) hypothyroidism and is the preferred replacement thyroid hormone in patients of all ages; other thyroid replacement hormones offer no discernable safety and efficacy advantage over levothyroxine.

Thyroid replacement therapy is not used in transient hypothyroidism during the recovery phase of subacute thyroiditis.

Using levothyroxine (T4) alone is sufficient in most individuals with hypothyroidism, including pediatric and pregnant patients.

Almost all patients receiving levothyroxine alone will become euthyroid; there are few individuals who need T3 supplementation in addition to T4 to treat symptoms or biochemical imbalance.

Levothyroxine is also the preferred agent when used as a diagnostic agent in TSH suppression tests as an aid in detecting hyperthyroidism, and as an adjunct agent in the treatment of well-differentiated thyroid cancer.

Intravenous levothyroxine is primarily used to treat myxedema coma, a medical emergency; oral replacement is not recommended until such patients are clinically stable.

Levothyroxine has been used clinically since the 1950s; marketed products are governed by modern FDA approval processes for safety, efficacy, purity, potency, and bioequivalence.

Indications

  1. cretinism
  2. hypothyroidism
  3. myxedema coma
  4. organ preservation
  5. thyroid cancer

Thyroid Products Equivalent Oral Dosages; listings are estimates only

Preparation – dosage equivalents – (T4: T3 ratio)

Levothyroxine – 0.1 mg – (1:0)

Liothyronine – 25 mcg – (0:1)

Liotrix-1 (levothyroxine; liothyronine synthetic)- 50 to 60 mcg/12.5 to 15 mcg – (4:1)

Thyroid USP (levothyroxine; liothyronine, porcine)- 60 mg (1 grain) – (2 to 5:1)

Side Effects

  1. abdominal pain
  2. alopecia
  3. amenorrhea
  4. angina
  5. angioedema
  6. anorexia
  7. anxiety
  8. appetite stimulation
  9. arrhythmia exacerbation
  10. arthralgia
  11. atrial fibrillation
  12. cardiac arrest
  13. craniosynostosis
  14. diarrhea
  15. dyspnea
  16. elevated hepatic enzymes
  17. emotional lability
  18. epiphyseal closure
  19. fatigue
  20. fever
  21. flushing
  22. growth inhibition
  23. headache
  24. heart failure
  25. heat intolerance
  26. hyperactivity
  27. hyperhidrosis
  28. hypertension
  29. hyperthyroidism
  30. increased intracranial pressure
  31. infertility
  32. insomnia
  33. irritability
  34. menstrual irregularity
  35. muscle cramps
  36. nausea
  37. osteopenia
  38. osteoporosis
  39. palpitations
  40. peripheral edema
  41. pruritus
  42. pseudotumor cerebri
  43. rash
  44. seizures
  45. serum sickness
  46. sinus tachycardia
  47. thyrotoxicosis
  48. tremor
  49. urticaria
  50. vomiting
  51. weakness
  52. weight loss
  53. wheezing

Monitoring Parameters

  • blood pressure
  • growth rate
  • heart rate
  • thyroid function tests (TFTs)
  • weight

Contraindications

  • acute myocardial infarction
  • adrenal insufficiency
  • angina
  • breast-feeding
  • cardiac arrhythmias
  • cardiac disease
  • coronary artery disease
  • diabetes mellitus
  • dysphagia
  • epiphyseal closure
  • geriatric
  • heart failure
  • hypertension
  • hyperthyroidism
  • hyponatremia
  • hypopituitarism
  • hypothermia
  • infertility
  • myocardial infarction
  • myxedema
  • obesity treatment
  • osteopenia
  • pregnancy
  • surgery
  • thyrotoxicosis
  • water intoxication

Interactions

  • Acarbose
  • Acetaminophen; Butalbital
  • Acetaminophen; Butalbital; Caffeine
  • Acetaminophen; Butalbital; Caffeine; Codeine
  • Acetohexamide
  • Albiglutide
  • Alendronate
  • Alendronate; Cholecalciferol
  • Alogliptin
  • Alogliptin; Metformin
  • Alogliptin; Pioglitazone
  • Alpha-glucosidase Inhibitors
  • Aluminum Hydroxide
  • Aluminum Hydroxide; Magnesium Carbonate
  • Aluminum Hydroxide; Magnesium Hydroxide
  • Aluminum Hydroxide; Magnesium Hydroxide; Simethicone
  • Aluminum Hydroxide; Magnesium Trisilicate
  • Amiodarone
  • Amobarbital
  • Amoxapine
  • Amoxicillin; Clarithromycin; Lansoprazole
  • Amoxicillin; Clarithromycin; Omeprazole
  • Asparaginase Erwinia chrysanthemi
  • Aspirin, ASA; Butalbital; Caffeine
  • Aspirin, ASA; Butalbital; Caffeine; Codeine
  • Aspirin, ASA; Omeprazole
  • Atropine; Hyoscyamine; Phenobarbital; Scopolamine
  • Azelastine; Fluticasone
  • Barbiturates
  • Beclomethasone
  • Belladonna Alkaloids; Ergotamine; Phenobarbital
  • Beta-agonists
  • Beta-blockers
  • Betamethasone
  • Budesonide
  • Budesonide; Formoterol
  • Butabarbital
  • Calcium
  • Calcium Acetate
  • Calcium Carbonate
  • Calcium Carbonate; Magnesium Hydroxide
  • Calcium Carbonate; Risedronate
  • Calcium Carbonate; Simethicone
  • Calcium Chloride
  • Calcium Gluconate
  • Calcium; Vitamin D
  • Canagliflozin
  • Canagliflozin; Metformin
  • Carbamazepine
  • Chlorpropamide
  • Cholestyramine
  • Chromium
  • Ciclesonide
  • Cocaine
  • Colesevelam
  • Colestipol
  • Corticosteroids
  • Cortisone
  • Cyclosporine
  • Dapagliflozin
  • Dapagliflozin; Metformin
  • Dapagliflozin; Saxagliptin
  • Deflazacort
  • Dexamethasone
  • Dexlansoprazole
  • Didanosine, ddI
  • Digoxin
  • Dulaglutide
  • Empagliflozin
  • Empagliflozin; Linagliptin
  • Empagliflozin; Linagliptin; Metformin
  • Empagliflozin; Metformin
  • enteral feedings
  • Ertugliflozin; Metformin
  • Ertugliflozin; Sitagliptin
  • Esomeprazole
  • Esomeprazole; Naproxen
  • Estrogens
  • Ethinyl Estradiol; Norethindrone Acetate; Ferrous fumarate
  • Ethinyl Estradiol; Norethindrone; Ferrous fumarate
  • Exenatide
  • Fludrocortisone
  • Flunisolide
  • Fluoxymesterone
  • Fluticasone
  • Fluticasone; Salmeterol
  • Fluticasone; Umeclidinium; Vilanterol
  • Fluticasone; Vilanterol
  • food
  • Formoterol; Mometasone
  • Furosemide
  • Glimepiride
  • Glimepiride; Pioglitazone
  • Glimepiride; Rosiglitazone
  • Glipizide
  • Glipizide; Metformin
  • Glyburide
  • Glyburide; Metformin
  • Hetastarch; Dextrose; Electrolytes
  • Hydantoins
  • Hydrocortisone
  • Imatinib
  • Indinavir
  • Insulin Degludec; Liraglutide
  • Insulin Glargine; Lixisenatide
  • Insulins
  • Iodine; Potassium Iodide, KI
  • Iodoquinol
  • Iohexol
  • Iopamidol
  • Iopromide
  • Ioversol
  • Iron
  • Iron Salts
  • Iron Sucrose, Sucroferric Oxyhydroxide
  • Isoniazid, INH; Pyrazinamide, PZA; Rifampin
  • Isoniazid, INH; Rifampin
  • Isosulfan Blue
  • Ketamine
  • L-Asparaginase Escherichia coli
  • Lansoprazole
  • Lansoprazole; Naproxen
  • Lanthanum Carbonate
  • Linagliptin
  • Linagliptin; Metformin
  • Liraglutide
  • Lithium
  • Lixisenatide
  • Magnesium
  • Maprotiline
  • Meglitinides
  • Mephobarbital
  • Metformin
  • Metformin; Pioglitazone
  • Metformin; Repaglinide
  • Metformin; Rosiglitazone
  • Metformin; Saxagliptin
  • Metformin; Sitagliptin
  • Methimazole
  • Methohexital
  • Methylprednisolone
  • Miglitol
  • Mometasone
  • Non-Ionic Contrast Media
  • Omeprazole
  • Omeprazole; Amoxicillin; Rifabutin
  • Omeprazole; Sodium Bicarbonate
  • Orlistat
  • Pantoprazole
  • Pentobarbital
  • Phenobarbital
  • Pioglitazone
  • Polycarbophil
  • Polysaccharide-Iron Complex
  • Potassium Iodide, KI
  • Pramlintide
  • Prednisolone
  • Prednisone
  • Primidone
  • Propylthiouracil, PTU
  • Proton pump inhibitors
  • Rabeprazole
  • Raloxifene
  • Rifampin
  • Rosiglitazone
  • Saxagliptin
  • Secobarbital
  • Semaglutide
  • Sevelamer
  • Simethicone
  • Simvastatin; Sitagliptin
  • Sitagliptin
  • Sodium Ferric Gluconate Complex; ferric pyrophosphate citrate
  • Sodium Iodide
  • Sodium Polystyrene Sulfonate
  • Somatropin, rh-GH
  • Sucralfate
  • Sulfonylureas
  • Sympathomimetics
  • Teduglutide
  • Theophylline, Aminophylline
  • Thiazolidinediones
  • Thiopental
  • Tirofiban
  • Tolazamide
  • Tolbutamide
  • Tretinoin, ATRA
  • Triamcinolone
  • Tricyclic antidepressants
  • Warfarin
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