Generic Name and Formulations:
Levothyroxine sodium 100mcg, 200mcg, 500mcg; pwd for IV inj after reconstitution.
Various generic manufacturers
Caution when converting from oral to intravenous levothyroxine.
Individualize. Initially 300–500mcg IV once, then 50–100mcg IV once daily; switch to oral form and dose as soon as feasible. Elderly, underlying cardiovascular disease: may need lower doses.
Not for treatment of obesity or weight loss. Adults: Monitor TSH 6–8 weeks after dose change then every 6–12 months. Peds: Monitor TSH 2 and 4 weeks after initiation, 2 weeks after dose change then every 3–12 months thereafter. Cardiovascular disease; monitor for cardiac arrhythmias during surgery. Reduce or withhold dose for 1 week if cardiac symptoms develop or worsen; restart at lower dose. Tabs: not for treating myxedema coma. Correct adrenal insufficiency before initiation. Increased sensitivity in severe hypothyroidism. Diabetes; monitor glucose control. Use lowest effective dose. Elderly. Pregnancy: monitor TSH at least every trimester; adjust dose and do not discontinue (see full labeling). Nursing mothers.
See full labeling. Absorption reduced by some foods (eg, soy flour, cottonseed meal, walnuts, fiber, grapefruit juice), aluminum and magnesium hydroxide, simethicone, proton pump inhibitors, iron, sucralfate; monitor. Give at least 4hrs apart from calcium carbonate, ferrous sulfate, bile acid sequestrants (eg, colesevelam, cholestyramine, colestipol), ion exchange resins (eg, kayexalate, sevelamer). Potentiates, and is potentiated by, tri- and tetracyclic antidepressants. Concomitant sympathomimetics; monitor for coronary insufficiency. Antagonized by phenobarbital, rifampin, sertraline. Antagonizes digitalis glycosides. Marked hypertension and tachycardia with ketamine. Hypothyroidism risk with concomitant tyrosine kinase inhibitors (eg, imatinib). Estrogens, androgens, corticosteroids affect thyroid function tests. Monitor oral anticoagulants, antidiabetic agents, orlistat.
Arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, skin rash; seizures (rare); Children: pseudotumor cerebri, slipped capital femoral epiphysis.
Tabs (all)—90, 1000; Tabs (25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 125mcg, 175mcg)—100; Single-use vials—1
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