Levothyroxine Sodium (L-Thyroxine, T4)(lee voe thye rox’ een)
Levothroid, Levoxine, Levoxyl, Synthroid Thyro-Tabs
PREGNANCY CATEGORY A
Drug class
Thyroid hormone
Therapeutic Actions
Increases the metabolic rate of body tissues, thereby increasing oxygen consumption; respiration and HR; rate of fat, protein, and carbohydrate metabolism; and growth and maturation.
Indications
Replacement therapy in hypothyroidism
Pituitary TSH suppression in the treatment and prevention of euthyroid goiters and in the management of thyroid cancer
Treatment of thyrotoxicosis in conjunction with antithyroid drugs and to prevent goitrogenesis, hypothyroidism, and thyrotoxicosis during pregnancy
Treatment of myxedema coma
Contraindications and Cautions
Contraindicated with allergy to active or extraneous constituents of drug, untreated thyrotoxicosis, and acute MI uncomplicated by hypothyroidism.
Use cautiously with Addison disease (treat hypoadrenalism with corticosteroids before thyroid therapy), lactation, patients with coronary artery disease or angina.
Available Forms
Tablets—25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, 300 mcg; powder for injection—200, 500 mcg/vial; capsules—13, 25, 50, 75, 100, 125, 150 mcg
Dosages
50–100 mcg equals approximately 60 mg (1 grain) desiccated thyroid.
Adults
Hypothyroidism: Initial dose, 12.5–25 mcg PO, with increasing increments of 25 mcg PO every 2–4 wk; maintenance up to 200 mcg/day. IV or IM injection can be substituted for the oral dosage form when oral ingestion is not possible. Usual IV dose is 50% of oral dose. Start at 25 mcg/day or less in patients with long-standing hypothyroidism or known cardiac disease. Usual replacement 1.7 mcg/kg per day.
Myxedema coma without severe heart disease: 200–500 mcg IV as initial dose. An additional 100–300 mcg or more may be given the second day if necessary. Switch to PO once patient is able. Full effect not seen for 24 hr; dose based on improvement.
TSH suppression in thyroid cancer, nodules, and euthyroid goiters: Doses should be individualized based on specific disease and patient. Larger amounts than used for normal suppression.
Thyroid suppression therapy: 2.6 mcg/kg/day PO for 7–10 days.
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