Drug Index

Levothyroxine Sodium

 
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Synonym :

Thyroxine

Mechanism :

Levothyroxine is a thyroid hormone, 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 :

• Hypothyroidism


Contraindications :

Levothyroxine sodium is contraindicated in patients with untreated thyrotoxicosis or an apparent hypersensitivity to thyroid hormones. Levothyroxine sodium is also contraindicated in the patients with uncorrected adrenal insufficiency.


Dosing :

1-3 months: 10-15 microgram/kg orally OR 5-7.5 microgram/kg/day either intravenously or IM; 3-6 months: 8-10 microgram/kg orally everyday OR 25-50 microgram/day.

6-12 months: 6-8 microgram/kg orally everyday OR 75-100 microgram/day orally.

1-5 years: 5-6 mcg/kg orally everyday OR 75-100 microgram/day orally.

6-12 years: 4-5 microgram/kg orally everyday OR 100-125 microgram/day orally.

>12 years, growth/puberty incomplete: 2-3 microgram/kg orally everyday OR 150 mcg/day PO.

Start with lower dose and increase every 4-6 weeks if risk for cardiac failure; adjust dose based on Thyroid function tests. Give oral form on empty stomach; IM/IV dose is 50-75% of PO dose.


Adverse Effect :

Iatrogenic hyperthyroidism in infants receiving thyroid hormone replacement therapy has been associated with craniosynostosis. Partial hair loss may occur during the initial months of therapy but is generally transient. Hypersensitivity reactions such as rash and urticaria, may occur. With excessive dose: tachycardia, sweating, cramps, excitability, headache, palpitations, cardiac arrhythmias, and diarrhea. Pseudotumor cerebri has been reported in pediatric patients receiving thyroid hormone replacement therapy.


Interaction :

Aluminium Hydroxide, Cholestyramine Resin, Colestipol Hydrochloride, Ferrous Sulfate, Sodium Polystyrene Sulfonate, Sucralfate: Decrease absorption of levothyroxine sodium from the gastrointestinal tract.
Amiodarone: Amiodarone therapy alone can cause hypothyroidism or hyperthyroidism.
Anticoagulants (Oral): The hypoprothrombinemic effect of anticoagulants may be potentiated, apparently by increased catabolism of vitamin K-dependent clotting factors.
Antidiabetic Agents (Insulin, Sulfonylureas): Requirements for insulin or oral antidiabetic agents may be reduced in hypothyroid patients with diabetes mellitus and may subsequently increase with the initiation of thyroid hormone replacement therapy.
Beta-Adrenergic Blocking Agents: Actions of some of beta-blocking agents may be impaired when hypothyroid patients become euthyroid.
Cytokines (interferon, interleukin): Cytokines have been reported to induce both hyperthyroidism and hypothyroidism.
Digitalis Glycosides: Therapeutic effects of digitalis glycosides may be reduced. Serum digitalis levels may be decreased in hyperthyroidism or when a hypothyroid patient becomes euthyroid.
Ketamine: Marked hypertension and tachycardia have been reported in association with concomitant administration of levothyroxine sodium and ketamine.
Somatropin: Excessive concurrent use of thyroid hormone may accelerate epiphyseal closure. Untreated hypothyroidism may interfere with the growth response to somatrem or somatropin.
Theophylline: Theophylline clearance may decrease in hypothyroid patients and return toward normal when a euthyroid state is achieved.
Tricyclic Antidepressants: Concurrent use may increase the therapeutic and toxic effects of both drugs, possibly due to increased catecholamine sensitivity.
Sympathomimetic Agents: Possible increased risk of coronary insufficiency in patients with coronary artery disease.


07/14/2019 19:51:41 Levothyroxine Sodium
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