February 19, 2017
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Brand Name: Levothyroxine

Generic Name: levothyroxine

Drug Class: Thyroid products

What Is Levothyroxine and How Does It Work?

Levothyroxine is a thyroid product used to treat an underactive thyroid (hypothyroidism). It replaces or provides more thyroid hormone, which is normally produced by the thyroid gland. Low thyroid hormone levels can occur naturally or when the thyroid gland is injured by radiation/medications or removed by surgery. Having enough thyroid hormone is important for maintaining normal mental and physical activity. In children, having enough thyroid hormone is important for normal mental and physical development.

Levothyroxine is also used to treat other types of thyroid disorders (such as certain types of goiters, thyroid cancer).

Levothyroxine should not be used to treat infertility unless it is caused by low thyroid hormone levels.

Levothyroxine is available under the following different brand names: Synthroid, Levoxyl, L Thyroxine, Levo T, Levothroid, Levothyroxine T4, Levoxine, Tirosint, and Unithroid.

Dosages of Levothyroxine Should Be Given As Follows:

Adult and Pediatric Dosage Forms & Strengths

  • 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg
  • 25mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg
Capsule (Tirosint)
  • 13mcg, 25mcg, 50mcg, 75mcg, 88mcg
  • 100mcg, 112 mcg, 125mcg, 137 mcg, 150mcg
Powder for injection
  • 100mcg/vial
  • 200mcg/vial
  • 500mcg/vial

Dosage Considerations

Mild Hypothyroidism

1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day

>50 years (or <50 yr with CV disease)

  • Usual initial dose: 25-50 mcg/day
  • May adjust dose by 12.5-25 mcg q6-8Week
>50 yr with CV disease
  • Usual initial dose: 12.5-25 mcg PO qDay
  • May adjust dose by 12.5-25 mcg q4-6weeks until patient becomes euthyroid and serum TSH concentration normalized; adjustments q6-8weeks also used
  • Dose range: 100-125 mcg PO qDay

Severe Hypothyroidism

Initial: 12.5-25 mcg PO qDay

Adjust dose by 25 mcg/day q2-4Week PRN

Subclinical Hypothyroidism

Initial: 1 mcg/kg PO qDay may be adequate, OR

If replacement therapy not initiated, monitor patient annually for clinical status

Myxedema Coma

300-500 mcg IV once, THEN 50-100 mcg qDay until patient is able to tolerate oral administration; may consider smaller doses in patients with cardiovascular disease

Organ Preservation (Orphan)

Preservation of organ function in brain-dead organ donors

Orphan indication sponsor: Fera Pharmaceuticals, LLC; 134 Birch Hill Road; Locust Valley, NY 11560

Dosing Considerations

Avoid undertreatment or overtreatment, which may result in adverse effects.

Initiate lower dose in elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism.

Long-term therapy decreases bone mineral density; use lowest dose in postmenopausal women and women using suppressive doses.

Lower dose of Tirosint capsules may be required compared with standard T4 tablets for hypothyroidism in patients with impaired gastric acid secretion to reach their target TSH levels; Tirosint has shown improved absorption compared with conventional T4 tablets

Check for bioequivalence if switching brands/generics, OR every week after switching from one levothyroxine sodium preparation to another.

Monitor serum thyroid levels; patient may be asymptomatic


  • Initially evaluate patients q6-8Week
  • Once normalization of thyroid function and serum TSH concentration achieved, evaluate q6-12mo


Take tabs with full glass of water preferably 30 min to 1 hr before breakfast on empty stomach

Do not use foods that decrease absorption (soybean products) for administering levothyroxine

Administer oral levothyroxine >4 hr apart from drugs known to interfere with absorption

IV/IM 50% of PO

Patients unable to swallow intact tabs

  • Crush appropriate dose and place in 5-10 mL of water
  • Administer resultant suspension by spoon or dropper immediately, do NOT store

Medically Reviewed by a Doctor on 2/16/2017

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