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levothyroxine sodium (T4, l-thyroxine sodium)
Eltroxin†, Levo-T, Levothroid, Levoxine, Levoxyl, Oroxine‡, Synthroid**

Pregnancy Risk Category A

How supplied
Tablets:
25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Injection:
200-mcg vial, 500-mcg vial

Action
Not completely defined. Stimulates metabolism of all body tissues by accelerating rate of cellular oxidation.

Indications & dosage
Cretinism--

Children up to age 6 months:
25 to 50 mcg or 5 to 6 mcg/kg P.O. daily.
Children ages 6 to 12 months:
50 to 75 mcg or 5 to 6 mcg/kg P.O. daily.
Children ages 1 to 5:
75 to 100 mcg or 3 to 5 mcg/kg P.O. daily.
Children ages 6 to 12:
100 to 150 mcg or 4 to 5 mcg/kg P.O. daily.
Children over age 12:
over 150 mcg or 2 to 3 mcg/kg P.O. daily.
Myxedema coma--

Adults:
200 to 500 mcg I.V.; then 100 to 300 mcg given on second day, followed by parenteral maintenance dose of 50 to 200 mcg I.V. daily. Switch patient to oral maintenance as soon as possible.
Thyroid hormone replacement--

Adults:
initially, 25 to 50 mcg P.O. daily, increased by 25 mcg P.O. q 2 to 4 weeks until desired response occurs. Maintenance dose is 75 to 200 mcg P.O. daily. May administer I.V. or I.M. when P.O. ingestion is precluded for long periods. However, dosage adjustment is needed.
Children:
in children under age 1, initial dose is 25 to 50 mcg P.O. daily; in children ages 1 and older, 3 to 5 mcg/kg P.O. daily. Gradually increased by 25 to 50 mcg q 2 to 4 weeks until desired response occurs.
Elderly:
for patients over age 65, 12.5 to 50 mcg P.O. daily. Increased by 12.5 to 25 mcg at 3- to 8-week intervals, depending on response.

Adverse reactions
CNS:
nervousness, insomnia, tremor, headache.
CV:
tachycardia, palpitations, arrhythmias, angina pectoris, cardiac arrest.
GI:
diarrhea, vomiting.
GU:
menstrual irregularities.
Metabolic:
weight loss.
Skin:
allergic skin reactions, diaphoresis.
Other:
heat intolerance, fever.

Interactions
Drug-drug.
Cholestyramine, colestipol: impaired levothyroxine absorption. Separate doses by 4 to 5 hours.
Estrogen
s: decreased free levothyroxines. Monitor for decreased effectiveness of thyroid hormone.
Insulin, oral antidiabetics:
altered serum glucose levels. Monitor blood glucose levels. Dosage adjustments may be needed.
I.V. phenytoin:
free thyroid released. Monitor for tachycardia.
Oral anticoagulants:
altered PT. Monitor PT and INR. Dosage adjustments may be needed.
Sympathomimetics such as epinephrine:
increased risk of coronary insufficiency. Monitor closely.

Effects on diagnostic tests
Alterations in radioactive iodine (131I) thyroid uptake, protein-bound iodine levels, and liothyronine uptake may occur.

Contraindications
Contraindicated in patients with hypersensitivity to drug and in those with acute MI uncomplicated by hypothyroidism, untreated thyrotoxicosis, or uncorrected adrenal insufficiency.

Nursing considerations

I.V. administration

Patient teaching

*Liquid contains alcohol. **May contain tartrazine.  †Canada  ‡Australia  §U.K.  OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING

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