Replacement or supplemental therapy in congenital or acquired hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis. Specific indications include primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) hypothyroidism.
Not considered drug of choice for replacement therapy because of potential problems (e.g., variability in T4:T3 ratio, fluctuating and often elevated T3 concentrations). Levothyroxine is considered drug of choice for replacement therapy.
For the treatment of congenital hypothyroidism (cretinism), levothyroxine is considered drug of choice.
Adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.
Efficacy of TSH suppression for benign nodular disease remains controversial.
Diagnosis of Thyroid Disorders
Used diagnostically in suppression tests to differentiate suspected mild hyperthyroidism or thyroid gland autonomy. Use with caution in patients in whom there is a strong suspicion of thyroid gland autonomy because exogenous hormone effects will be additive to endogenous source.
Thyrotoxicosis
Has been used in combination with antithyroid agents for the treatment of thyrotoxicosis to prevent goitrogenesis and hypothyroidism.
May occasionally be useful to prevent antithyroid agent-induced hypothyroidism in the management of thyrotoxicosis during pregnancy; however, combination therapy generally considered unnecessary because it may increase the requirement for antithyroid agents and, therefore, the risk of fetal hypothyroidism.
Other Uses
See Unlabeled Uses under Cautions.
Dosage and Administration
General
Initially, monitor response to therapy about every 6–8 weeks. Once normalization of thyroid function and serum TSH concentrations has been achieved, patients may be evaluated less frequently (i.e., every 6–12 months). However, if dosage is changed, measure serum TSH concentrations after 8–12 weeks.
Commercially available natural thyroid preparations have different T4:T3 ratios and fluctuating T3 concentrations. Do not switch from one manufacturer's natural thyroid preparation to another manufacturer's preparation unless under the direction and supervision of a clinician.
Natural and synthetic thyroid agent preparations are not necessarily directly comparable; however, the following equivalencies have been suggested based on clinical response:
Equivalencies of Thyroid Preparations Based on Clinical Response
Administer orally, usually as a single daily dose before breakfast.
Dosage
Each 65 mg of thyroid contains approximately 38 and 9 mcg of measurable levothyroxine and T3, respectively. Each 60–65 mg of thyroid is approximately clinically equivalent to 100 mcg or less of levothyroxine sodium or to 25 mcg of liothyronine sodium. (See General under Dosage and Administration.)
Adjust dosage carefully according to clinical and laboratory response to treatment. Avoid undertreatment or overtreatment. (See Therapy Monitoring under Cautions.)
Initiate dosage at a lower level in geriatric patients, in patients with functional or ECG evidence of cardiovascular disease, and in patients with severe, long-standing hypothyroidism or other endocrinopathies.
Pediatric Patients
Hypothyroidism
Oral
Initiate therapy at full replacement dosages as soon as possible after diagnosis of hypothyroidism to prevent deleterious effects on intellectual and physical growth and development. The following dosages have been recommended:
Dosage for Management of Hypothyroidism in Pediatric Patients
Age
Daily Dosage
0–6 months
15–30 mg or 4.8–6 mg/kg
6–12 months
30–45 mg or 3.6–4.8 mg/kg
1–5 years
45–60 mg or 3–3.6 mg/kg
6–12 years
60–90 mg or 2.4–3 mg/kg
>12 years
>90 mg or 1.2–1.8 mg/kg
When transient hypothyroidism is suspected, therapy may be temporarily discontinued when the child is >3 years of age to reassess the condition. (See Pediatric Use under Cautions.)
Adults
Hypothyroidism
Oral
Usual initial dosage is 15–30 mg daily. May increase dosage in increments of 15 mg at intervals of 2–3 weeks.
For management of long-standing myxedema, usual initial dosage is 15 mg daily.
Usual maintenance dosage is 60–120 mg daily. Failure to respond adequately to oral dosages of 180 mg daily suggests presence of malabsorption or patient noncompliance.
Pituitary TSH Suppression
Thyroid Cancer
Oral
Administration of dosages higher than those used for replacement therapy usually is required to suppress TSH concentrations to low or undetectable concentrations.
Special Populations
Patients with Cardiovascular Disease
Hypothyroidism
Initiate therapy at lower dosages than those recommended in patients without cardiovascular disease.
Usual initial dosage is 15–30 mg daily. If angina appears or if cardiovascular disease is aggravated, reduce dosage or temporarily withhold therapy and then cautiously restart therapy at a lower dosage.
Geriatric Patients
Hypothyroidism
Initiate therapy at lower dosages than those recommended in younger patients.
Usual initial dosage is 15–30 mg daily. If cardiovascular disease is aggravated, reduce dosage or temporarily withhold therapy and then cautiously restart therapy at a lower dosage.
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