Alternate Name(s):
Eltroxin, Synthroid
Classification:
Thyroid Supplement
Original Date:
December 2008
Revised Date:
March 2016
Indications:
- Replacement or supplemental therapy in congenital hypothyroidism
Administration:
- PO
- Administer on an empty stomach at least 4 hours apart from calcium, iron and antacids
- IV direct: over 2 - 5 minutes (max 100 mcg/min)
Dosage:
PO:
- Initial starting dose:
- 0 - 3 months: 10 - 15 mcg/kg/day once daily
- 3 - 6 months: 8 - 10 mcg/kg/day once daily
- Available as 25 mcg tablet. Round dose to the nearest 1/4 tablet
IV:
- 50 to 75% of the oral dose
- Infants and neonates with very low or undectable serum T4 levels should be started at higher end of the dosage range
- A lower dose should be considered for neonates at risk of cardiac failure, increasing every few days until a full maintenance dose is reached
- The dose should be adjusted based on clinical response and laboratory parameters
Side Effects:
Adverse reactions associated with levothyroxine sodium are primarily those of hyperthyroidism due to therapeutic overdosage
- CVS: palpitations, tachycardia, cardiac arrythmias, hypertension
- Dermatologic: hair loss
- GI: diarrhea, vomiting
Parameters to Monitor:
- BP, HR
- Measure TSH and free T4 two weeks after initiation of therapy and then at 2, 3, 6, 9 and 12 months of age in the first year of life. Titrate dose to normalize TSH and free T4 with follow-up measurements of TSH, free T4 at 4-6 weeks after dose adjustment.
Reconstitution and Stability:
- Levothyroxine 500 mcg (PPC)
- Add 5 mL of 0.9% NaCl
- Final concentration : 100 mcg/mL
Compatibility:
- Solution Compatible: 0.9% NaCl
Notes:
- Soybean formula decreases the absorption of levothyroxine
References:
1. Lau.E (Editor). Drug Handbook and Formulary - The Hospital for Sick Children. Toronto; 2015
2. Taketomo CK, Hodding JH, Kraus DM. Pediatric Dosage Handbook. 22nd Edition. Hudson: Lexi-Comp Inc.; 2015