Class: Thyroid Supplement
Dosage Forms. 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
Common FDA Label Indication, Dosing, and Titration.
1. Hypothyroidism: Oral: maintenance, individualized based on clinical response and serum TSH levels; Adults: 25-300 mcg po daily; Children: (0-3 mo) 10-15 mcg/kg/d po daily, (3-6 mo) 8-10 mcg/kg/d po daily, (6-12 mo) 6-8 mcg/kg/d po daily, (1-5 y) 5-6 mcg/kg/d po daily, (6-12 y) 4-5 mcg/kg/d po daily, (over 12 y, growth and puberty incomplete) 2-3 mcg/kg/d po daily, (growth and puberty complete) 1.7 mcg/kg/d
2. Thyroid-stimulating hormone suppression, pituitary: Thyroid cancer, doses >2 mcg/kg/d po are usually required to suppress TSH below 0.1 milliunits/L
1. Toxicity due to radiotherapy; use same age-based dosing as hypothyroidism
MOA. Levothyroxine sodium is a synthetic thyroid hormone. The endogenous thyroid hormones, T3 and T4, diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins.
Drug Characteristics: Levothyroxine
Medication Safety Issues: Levothyroxine
Drug Interactions: Levothyroxine
Adverse Reactions: Levothyroxine
Efficacy Monitoring Parameters. Serum TSH, T(3), and T(4) levels. T(3): normal range is 100-200 ng/dL. T(4): normal range is 4.5-11.2 mcg/dL. TSH level should be between 0.5 and 3.0 mIU/L in those treated for a thyroid disorder. Resolution of symptoms of hypothyroidism, fatigue, edema, hair loss, cold intolerance, and lethargy.
Toxicity Monitoring Parameters. Monitor patients with preexisting cardiovascular disease for exacerbation of symptoms.
Key Patient Counseling Points. May require 6-8 wk for symptomatic improvement. Avoid abrupt discontinuation. Take on an empty stomach, with water. Avoid anatacids and iron within 2 h of dose.
Clinical Pearls. Not recommended for weight loss. May cause serious adverse effects and death in euthymic patients using it for weight loss.