Drug class
Levothyroxine is a synthetic thyroid hormone (L-thyroxine/T4). It functions as a replacement therapy exerting "physiologic actions through control of DNA transcription and protein synthesis," maintain
Uses
Levothyroxine sodium tablets are indicated for: - Hypothyroidism: "replacement therapy in primary (thyroidal), secondary (pituitary) and tertiary (hypothalamic) congenital or acquired hypothyroidism" - TSH Suppression: "as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer" Limitations: Not for benign thyroid nodules/nontoxic goiter in iodine-sufficient patients or hypothyroidism during recovery from subacute thyroiditis. ---
Warnings
BOXED WARNING: "Thyroid hormones should not be used for the treatment of obesity or for weight loss. Larger doses may produce serious or even life threatening manifestations of toxicity." Major Warnings: - Cardiac risks: "Over-treatment may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias"—especially in elderly and cardiac disease patients - Myxedema coma: Do not use oral products; requires intravenous administration - Adrenal crisis: Treat adrenal insufficiency with glucocorticoids before initiating therapy - Narrow therapeutic index: Risk of adverse effects on growth, cardiac function, metabolism, and cognitive function from over/undertreatment - Diabetic control: May "worsen glycemic control and result in increased antidiabetic agent or insulin requirements" - Bone density: Over-replacement increases bone resorption ---
Side effects
Adverse reactions primarily result from "hyperthyroidism due to therapeutic overdosage" and include: - General: fatigue, weight loss, heat intolerance, fever, excessive sweating - CNS: headache, nervousness, anxiety, insomnia, tremors - Cardiovascular: palpitations, tachycardia, arrhythmias, angina, myocardial infarction - GI: diarrhea, vomiting, abdominal cramps - Other: muscle weakness, dyspnea, hair loss, menstrual irregularities In children: pseudotumor cerebri and slipped capital femoral epiphysis reported ---