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