Drug Index


Synonym :


Mechanism :

Thyroid hormones, T4 and T3 are transported into cells by passive and active mechanisms. T3 in cell cytoplasm and T3 generated from T4 within the cell diffuse into the nucleus and bind to thyroid receptor proteins, which appear to be primarily attached to DNA. Receptor binding leads to activation or repression of DNA transcription, thereby altering the amounts of mRNA and resultant proteins. Changes in protein concentrations are responsible for the metabolic changes observed in organs and tissues.

Indication :

  • Congenital Hypothyroidism
  • Non-toxic Goitre

Contraindications :

Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency, untreated thyrotoxicosis and apparent hypersensitivity to any of their active or extraneous constituents.

Dosing :

Congenital Hypothyroidism:
Starting dosage:
5 microgram orally once daily, with a 5 microgram increment every 3 to 4 days until the desired response is achieved. Infants a few months old may require only 20 mcg orally once daily for maintenance.
At 1 year:
50 mcg orally once daily may be required.
Above 3 years:
25-75 mcg orally once daily.
Nontoxic Goitre:
Start with 5 microgram orally once daily; can be increased by 5-10 microgram every 1-2 weeks. When the dose reaches 25 mcg orally once daily, it can be increased by 12.5 mcg or 25 mcg every 1-2 weeks. Maintenance dose is 75 microgram orally once daily.

Adverse Effect :

Rarely seen: cardiopulmonary arrest, phlebitis, hypotension, twitching, angina, myocardial infarction, hypertension, tachycardia, congestive heart failure, fever.

Interaction :

Oral Anticoagulants: Thyroid hormones appear to increase catabolism of vitamin K-dependent clotting factors. If oral anticoagulants are also being given, compensatory increases in clotting factor synthesis are impaired.
Insulin or Oral Hypoglycemics: Initiating thyroid replacement therapy may cause increases in insulin or oral hypoglycemic requirements.
Cholestyramine: Cholestyramine binds both T4 and T3 in the intestine, thus impairing absorption of these thyroid hormones. Therefore, 4 to 5 hours should elapse between administration of cholestyramine and thyroid hormones.
Estrogen, Oral Contraceptives: Estrogens tend to increase serum thyroxine-binding globulin (TBg). In a patient with a non-functioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine may be decreased when estrogens are started thus increasing thyroid requirements.
Tricyclic Antidepressants: Use of thyroid products with imipramine and other tricyclic antidepressants may increase receptor sensitivity and enhance antidepressant activity transient cardiac arrhythmias have been observed. Thyroid hormone activity may also be enhanced.
Digitalis: Thyroid preparations may potentiate the toxic effects of digitalis.
Ketamine: When administered to patients on a thyroid preparation, this parenteral anesthetic may cause hypertension and tachycardia. Use with caution and be prepared to treat hypertension, if necessary.
Vasopressors: Thyroxine increases the adrenergic effect of catecholamines such as epinephrine and norepinephrine. Therefore, injection of these agents into patients receiving thyroid preparations increases the risk of precipitating coronary insufficiency especially in patients with coronary artery disease.

Renal Dose :

Dose in Renal Impairment GFR (mL/min)
20-50Dose as in normal renal function
10-20Dose as in normal renal function
<10Dose as in normal renal function

Dose in Patients undergoing Renal Replacement Therapies
CAPDNot dialysed. Dose as in normal renal function
HDNot dialysed. Dose as in normal renal function
HDF/High fluxNot dialysed. Dose as in normal renal function
CAV/VVHDNot dialysed. Dose as in normal renal function

Hepatic Dose :

No dose adjustments are recommended.
01/19/2024 07:42:07 Liothyronine
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