Levothyroxine sodium (T₄)
Levothyroxine sodium
Levothyroxine sodium
(lee-voh-thigh-ROX-een)
Pregnancy Category: A Eltroxin Euthyrox Levo-T Levothroid Levoxyl PMS-Levothyroxine Synthroid L-Thyroxine Sodium (Rx)

Classification: Thyroid preparation

See Also: See also Thyroid Drugs .

Action/Kinetics: Levothyroxine is the synthetic sodium salt of the levoisomer of T₄ (tetraiodothyronine). Levothyroxine, 0.05-0.6 mg equals approximately 60 mg (1 grain) of thyroid. Absorption from the GI tract is incomplete and variable, especially when taken with food. Has a slower onset but a longer duration than sodium liothyronine. More active on a weight basis than thyroid. Is usually the drug of choice. Effect is predictable as thyroid content is standard. Time to peak therapeutic effect: 3-4 weeks. t1/2: 6-7 days in a euthyroid person, 9-10 days in a hypothyroid client, and 3-4 days in a hyperthyroid client. Is 99% protein bound. Duration: 1-3 weeks after withdrawal of chronic therapy. NOTE: All levothyroxine products are not bioequivalent; thus, changing brands is not recommended.

Drug Interactions: Concurrent use of aluminum hydroxide and levothyroxine may result in adsorption of levothyroxine to the aluminum and increased fecal elimination of levothyroxine.

How Supplied: Powder for injection: 0.2 mg, 0.5 mg; Tablet: 0.025 mg, 0.05 mg, 0.075 mg, 0.088 mg, 0.1 mg, 0.112 mg, 0.125 mg, 0.137 mg, 0.15 mg, 0.175 mg, 0.2 mg, 0.3 mg, 0.5 mg

Dosage
•Tablets Mild hypothyroidism.
Adults, initial: 50 mcg once daily; then, increase by 25-50 mcg q 2-3 weeks until desired clinical response is attained; maintenance, usual: 75-125 mcg/day (although doses up to 200 mcg/day may be required in some clients).
Severe hypothyroidism.
Adults, initial: 12.5-25 mcg once daily; then, increase dose, as necessary, in increments of 25 mcg at 2- to 3-week intervals.
Congenital hypothyroidism.
Pediatric, 12 years and older: 2-3 mcg/kg once daily until the adult daily dose (usually 150 mcg) is reached. 6-12 years of age: 4-5 mcg/kg/day or 100-150 mcg once daily. 1-5 years of age: 5-6 mcg/kg/day or 75-100 mcg once daily. 6-12 months of age: 6-8 mcg/kg/day or 50-75 mcg once daily. Less than 6 months of age: 8-10 mcg/kg/day or 25-50 mcg once daily.
•IM, IV Myxedematous coma.
Adults, initial: 400 mcg by rapid IV injection, even in geriatric clients; then 100-200 mcg/day, IV. Maintenance: 100-200 mcg/day, IV. Smaller daily doses should be given until client can tolerate PO medication.
Hypothyroidism.
Adults: 50-100 mcg once daily; pediatric, IV, IM: A dose of 75% of the usual PO pediatric dose should be given.