Levothyroxine
Administration
- Type: Endocrine, synthetic hormone
- Dosage Forms: Tablet 13mcg, 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg. IV 100mcg, 200mcg, 500mcg
- Routes of Administration: PO, IV
- Common Trade Names: Synthroid
Adult Dosing
- Myxedema coma: 300-500 mcg IV x1, then 50-100mcg IV daily until able to tolerate PO
- Hypothyroidism: doses vary
Pediatric Dosing
- Hypothyroid: Doses vary, 1.7-15 mcg/kg/day PO
Special Populations
- Pregnancy Rating: A
- Lactation risk: Infant risk minimal
- Renal dosing: Not defined
- Hepatic dosing: Not defined
Contraindications
- Allergy to class/drug, hypersensitivity to glycerol
- Uncorrected adrenal insufficiency (may precipitate acute adrenal crisis)
- Acute MI
- Subclinical or overt thyrotoxicosis, nontoxic diffuse goiter, nodular thyroid disease
Adverse Reactions
Serious
- MI, heart failure, tachycardia, cardiac arrest
- Pseudotumor, seizure
- Dyspnea
- Hyperthyroid
- Decreased bone mineral density, hip fracture
Common
- Palpitations
- Diarrhea
- Anxiety, insomnia, fatigue, sweating, weight loss
- Alopecia
Pharmacology
- Half-life: 6-7 days
- Metabolism: Hepatic
- Excretion: Renal, fecal
Mechanism of Action
- Synthetic thyroid hormone (T4)