Generic Name and Formulations:
Levothyroxine sodium 25mcg, 50mcg (dye-free), 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg; scored tabs.
Take in AM on empty stomach. Hypothyroidism: 1.7mcg/kg once daily. >50yrs, or <50yrs with cardiovascular disease: initially 25–50mcg once daily; titrate in increments of 12.5–25mcg every 6–8 weeks. Elderly with cardiovascular disease: initially 12.5–25mcg once daily; titrate in increments of 12.5–25mcg every 4–6 weeks. Usual max 200mcg/day. Severe hypothyroidism: initially 12.5–25mcg once daily; titrate in increments of 25mcg/day every 4 weeks. Subclinical hypothyroidism, secondary or tertiary hypothyroidism: see literature.
Give once daily on empty stomach. May crush tabs and mix in 5–10mL water. Hypothyroidism: 0–3months: 10–15mcg/kg per day; 3–6months: 8–10mcg/kg per day; 6–12months: 6–8mcg/kg per day; 1–5yrs: 5–6mcg/kg per day; 6–12yrs: 4–5mcg/kg per day; >12yrs: 2–3mcg/kg per day; growth and puberty complete: as adult. Chronic or severe hypothyroidism: initially 25mcg/day; titrate in increments of 25mcg every 4 weeks. Infants with serum T4<5mcg/dL: initially 50mcg/day.
Uncorrected adrenal insufficiency. Untreated thyrotoxicosis. Acute MI.
Not for treatment of obesity or infertility. Cardiovascular disease. Seizures. Adrenocortical insufficiency. Increased sensitivity in severe hypothyroidism. Autonomous thyroid tissue. Myxedema coma: use IV levothyroxine. Elderly. Pregnancy (Cat. A); do not discontinue due to pregnancy. Nursing mothers.
See literature. Absorption reduced by some foods (e.g., soy, fiber), aluminum and magnesium hydroxide, simethicone, calcium carbonate, sodium polystyrene sulfonate, bile acid sequestrants, iron, sucralfate (give at least 4 hrs apart). Potentiates, and is potentiated by, tri- and tetracyclic antidepressants, sympathomimetics. Antagonized by hepatic enzyme inducers (e.g., carbamazepine, phenytoin, phenobarbital, rifampin), sertraline. Antagonizes digoxin. Marked hypertension and tachycardia with ketamine. Estrogens affect thyroid function tests. Monitor oral anticoagulants, antidiabetic agents, theophylline.
Hyperthyroidism, decreased bone mineral density, transient alopecia; seizures (rare); pseudotumor cerebri in children.
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