Synthroid (levothyroxine) Dosage Guide

Synthroid (levothyroxine) Dosage Guide

LEVOTHYROXINE (lee-voe-thye-rox-een) Levo-T, Levothroid, Levoxyl, Synthroid hormone (thyroid preparation) Pregnancy Category A

INDICATIONS: Diminished or absent thyroid function.

Therapeutic Effects:  Restoration of normal hormonal balance.

  • DOSAGE Guide:

PO: Adults: 75–125 ug/d (1.5 ug/kg/d).

Geriatric Patients: 75 ug/d. Children > 10 yr: 150–200 ug/d (2–3 ug/kg/d).

Children 6–10 yr: 100–150 ug/d (4–5 ug/kg/d.)

Children 1–5 yr: 75–100 ug/d (3–5 ug/kg/d).

Children 6–12 mo: 50–75 ug/d (5–6 ug/kg/d).

IM, IV: Adults: Hypothyroidism: 50–100 ug/d. Myxedema coma/stupor: 200–500 ug IV.

Children:Hypothyroidism: 75% of the calculated oral dose.


Administer as a single dose, before breakfast. Direct IV: Dilute with 0.9% NaCl without preservatives, for a concentration of 100 ug/mL. Rate: 100 ug over 1 min.


Insomnia, irritability, nervousness, CARDIOVASCULAR COLLAPSE, arrhythmias, tachycardia, angina pectoris, hypertension, diarrhea, vomiting, hair loss (in children), increased sweating, hyperthyroidism, menstrual irregularities, weight loss, heat intolerance, accelerated bone maturation in children.


Hypersensitivity, recent MI, thyrotoxicosis.


Bile acid sequestrants decrease absorption of orally administered thyroid preparations.

  • May alter the effectiveness of warfarin.
  • May cause an increase in the requirement for insulin or oral hypoglycemic agents in diabetics.
  • Concurrent estrogen therapy may increase thyroid replacement requirements.
  • Additive cardiovascular effects with adrenergics (sympathomimetics).
  • May decrease response to beta-blockers.
  • Dose should be withheld and health care professional notified if resting pulse >100 bpm.

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