Indications for Levothyroxine Sodium Injection:
Limitations of Use:
Caution when converting from oral to IV 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.
Levothyroxine Sodium Injection Contraindications:
Uncorrected adrenal insufficiency.
Not for treatment of obesity or for weight loss.
Levothyroxine Sodium Injection Warnings/Precautions:
Underlying cardiovascular disease. Monitor for cardiac arrhythmias during surgery in those with coronary artery disease. Reduce or withhold dose for 1 week if cardiac symptoms develop or worsen; restart at lower dose. Myxedema coma: use IV levothyroxine. Adults: Monitor TSH 6–8 weeks after dose change then every 6–12 months when stable. Peds: Monitor TSH and total or free-T4 at 2 and 4 weeks after initiation, 2 weeks after dose change then every 3–12 months thereafter. Correct adrenal insufficiency before initiation. Diabetes; monitor glycemic control. Increased bone resorption and decreased BMD (esp. in post-menopausal women). Use lowest effective dose. Elderly. Pregnancy: monitor TSH/free-T4 at least every trimester; adjust dose and do not discontinue (see full labeling). Nursing mothers.
Levothyroxine Sodium Injection Classification:
Levothyroxine Sodium Injection Interactions:
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, sevelamer, lanthanum, bile acid sequestrants (eg, colesevelam, cholestyramine, colestipol), ion exchange resins (eg, kayexalate). Thyroid levels may be affected by clofibrate, estrogens, heroin, methadone, 5-fluorouracil, mitotane, tamoxifen, androgens, anabolic steroids, asparaginase, glucocorticoids, nicotinic acid (slow-release), salicylates (>2g/day), β-blockers (eg, propranolol), glucocorticoids, amiodarone. Monitor thyroid parameters with concomitant carbamazepine, furosemide (>80mg IV), heparin, hydantoins, NSAIDs. 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). Monitor with 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.
Generic Drug Availability:
Tabs (all)—90, 1000; Tabs (50mcg, 75mcg, 100mcg, 125mcg, 150mcg, 200mcg)—100; Single-use vials—contact supplier