Classifications: hormone; thyroid hormone replacement;
Therapeutic: thyroid hormone replacement

Prototype: Levothyroxine sodium
Pregnancy Category: A


0.0125 mcg, 3.1 mcg, 6.25 mcg, 12.5 mcg, 25 mcg, 37.5 mcg


Synthetic levothyroxine (T4) and liothyronine (T3) combined in a constant 4:1 ratio by weight. Thyroid hormones influence growth and maturation of tissues, increase energy expenditure, and affect turnover of essentially all substrates. These hormones play an integral role in metabolic processes, and are important to development of the CNS in newborns.

Therapeutic Effect

Increases metabolic rate of all body tissues.


Replacement or supplemental therapy for cretinism, myxedema, goiter, and secondary (pituitary) or tertiary (hypothalamic) hypothyroidism. Also with antithyroid agents in thyrotoxicosis and to prevent goitrogenesis and hypothyroidism.


Untreated thyrotoxicosis, acute MI, morphologic hypogonadism, nephrosis, adrenal deficiency due to hypopituitarism; tartrazine dye hypersensitivity, obesity treatment.

Cautious Use

Concomitant anticoagulant therapy; myxedema; hypertension, angina, cardiac arrhythmias, cardiac disease, coronary artery disease; older adults; hypertension; neonates, infants, children; arteriosclerosis; kidney dysfunction, pregnancy (category A), lactation.

Route & Dosage

Thyroid Replacement
Adult/Child: PO 12.5–30 mcg/d, gradually increase to desired response


  • Give as a single daily dose, preferably before breakfast.
  • Make dose increases at 1- to 2-wk intervals.
  • Store in heat-, light-, and moisture-proof container. Shelf-life: 2 y.

Adverse Effects (≥1%)

CNS: Nervousness, headache, tremors, insomnia. CV: Palpitation, tachycardia, angina pectoris, cardiac arrhythmias, hypertension, CHF. GI: Nausea, abdominal cramps, diarrhea. Body as a Whole: Weight loss, heat intolerance, fever, sweating, menstrual irregularities. Musculoskeletal: Accelerated rate of bone maturation in infants and children.


Drug: Cholestyramine, colestipol decrease absorption; epinephrine, norepinephrine increase risk of cardiac insufficiency; oral anticoagulants may potentiate hypoprothrombinemia.


Not studied.

Nursing Implications

Assessment & Drug Effects

  • Watch for possible additive effects during the early period of liothyronine substitution for another preparation, particularly in older adults, children, and patients with cardiovascular disease. Residual actions of other thyroid preparations may persist for weeks.
  • Note: Metabolic effects of liotrix persist a few days after drug withdrawal.
  • Withhold drug for 1–2 d at onset of overdosage symptoms (hyperthyroidism, see Appendix F); usually therapy can be resumed with lower dosage.
  • Monitor diabetics for glycemic control; an increase in insulin or oral hypoglycemic may be required.

Patient & Family Education

  • Follow directions for taking this drug (see ADMINISTRATION).
  • Notify physician of headache (euthyroid patients); may indicate need for dosage adjustment or change to another thyroid preparation.
  • Take medication exactly as ordered.
  • Learn S&S of hyperthyroidism (see Appendix F); notify physician if they appear.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 02/01/2023 (0)
Wait 20 seconds...!!!