Generic name: levothyroxine sodium
Dosage form: capsule
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Important Information Before Use
Do not cut or crush TIROSINT capsules; capsules should be swallowed whole.
Administer TIROSINT as a single daily dose, preferably one-half to one hour before breakfast. Administer at least 4 hours before or after drugs and foods that are known to interfere with TIROSINT absorption [See Drug Interactions (7.1, 7.9) and Clinical Pharmacology (12.3)].
Principles of Dosing
The goal of replacement therapy is to achieve and maintain a clinical and biochemical euthyroid state. The goal of suppressive therapy is to inhibit growth and/or function of abnormal thyroid tissue. The dose of TIROSINT that is adequate to achieve these goals depends on a variety of factors including the patient's age, body weight, cardiovascular status, concomitant medical conditions, pregnancy status, concomitant medications, and the specific nature of the condition being treated.
Hence, the following recommendations serve only as dosing guidelines. Dosing must be individualized and adjustments made based on periodic assessment of the patient's clinical response and laboratory parameters. Inadequate levothyroxine dosage will fail to ameliorate the signs and symptoms of hypothyroidism [See Warnings and Precautions (5.1)].
Due to the long half-life of levothyroxine, the peak therapeutic effect at a given dose of levothyroxine sodium may not be attained for 4-6 weeks.
Dosing In Specific Patient Populations
Hypothyroidism in Adults and in Adolescents in Whom Growth and Puberty are Complete
The average full replacement dose of levothyroxine sodium is approximately 1.7 mcg per kg per day (e.g., 100-125 mcg per day for a 70 kg adult). Elderly patients may require less than 1 mcg per kg per day.
The initial levothyroxine dosage is based on the age, weight, and cardiac status of the patient as well as the severity and duration of the hypothyroidism. Therapy may generally begin at full replacement doses in otherwise non-elderly, healthy individuals.
For elderly patients or those with underlying cardiovascular disease, a starting dose of levothyroxine sodium as low as 12.5 mcg per day may be appropriate, with gradual increments in dose at 6-8 week intervals, as needed [See Warnings and Precautions (5.2)]. More frequent monitoring is recommended for patients with more severe hypothyroidism.
In general, levothyroxine sodium doses greater than 200 mcg per day are seldom required. An inadequate response to daily doses greater than 300 mcg per day is rare and may indicate poor compliance, malabsorption, and/or drug interactions.
Secondary or Tertiary Hypothyroidism
In patients with secondary (pituitary) or tertiary (hypothalamic) hypothyroidism, the levothyroxine sodium dose should be titrated until the patient is clinically euthyroid and the serum free thyroxine (FT4) level is restored to the upper half of the normal range.
Hypothyroidism (Congenital or Acquired) in the Pediatric Population
Only administer TIROSINT to children who are able to swallow an intact capsule [See Contraindications (4)].
In general, levothyroxine therapy should be instituted at full replacement doses as soon as possible. Delays in diagnosis and institution of therapy may have deleterious effects on the child's intellectual and physical growth and development. Undertreatment and overtreatment should be avoided [See Warnings and Precautions (5.1) and Use in Specific Populations (8.4)].
Levothyroxine therapy is usually initiated at full replacement doses, with the recommended dose per body weight changing with age (Table 1).
|Age||Daily Dose Per Kg Body Weight*|
|6-12 years||4-5 mcg/kg/day|
|>12 years but growth and puberty incomplete||2-3 mcg/kg/day|
|Growth and puberty complete||1.7 mcg/kg/day|
In children with chronic or severe hypothyroidism, a lower initial dose of 25 mcg per day of levothyroxine sodium is recommended with increasing increments of 25 mcg every 2-4 weeks until the desired effect is achieved.
Hyperactivity in an older child can be minimized if the starting dose is one-fourth of the recommended full replacement dose, and the dose is then increased on a weekly basis by an amount equal to one-fourth the full-recommended replacement dose until the full recommended replacement dose is reached.
Pregnancy may increase levothyroxine requirements. [See Use in Specific Populations (8.1)]
Thyrotropin-Stimulating Hormone (TSH) Suppression in Well-Differentiated Thyroid Cancer
In the treatment of well-differentiated (papillary and follicular) thyroid cancer, levothyroxine is used as an adjunct to surgery and radioiodine therapy. Generally, TSH is suppressed to less than 0.1 mU per L, and this usually requires a levothyroxine sodium dose of greater than 2 mcg per kg per day. However, in patients with high-risk tumors, the target level for TSH suppression may be less than 0.01 mU per L.
Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism, and may result in unpredictable absorption of levothyroxine sodium from the gastrointestinal tract. Therefore, thyroid hormone administered intravenously is the recommended route of administration in this rare condition.
Monitoring TSH and/or Thyroxine (T4) Levels
The adequacy of therapy is determined by periodic assessment of appropriate laboratory tests and clinical evaluation. The choice of laboratory tests depends on various factors including the etiology of the underlying thyroid disease, the presence of concomitant medical conditions, including pregnancy, and the use of concomitant medications. Persistent clinical and laboratory evidence of hypothyroidism despite an apparent adequate replacement dose of TIROSINT may be evidence of inadequate absorption, poor compliance, drug interactions, or decreased T4 potency of the drug product.
In adult patients with primary (thyroidal) hypothyroidism, serum TSH levels alone may be used to monitor therapy. The frequency of TSH monitoring during levothyroxine dose titration depends on the clinical situation but reassessment and titration should be done after an interval of at least 6 weeks after any change in dose. When the optimum replacement dose has been attained, clinical (physical examination) and biochemical monitoring may be performed every 6-12 months, depending on the clinical situation, and whenever there is a change in the patient's status. It is recommended that a physical examination and a serum TSH measurement be performed at least annually in patients receiving TIROSINT.
In patients with congenital hypothyroidism, the adequacy of replacement therapy should be assessed by measuring both serum TSH and total or FT4. While the aim of therapy is to also normalize the serum TSH level, this is not always possible in a small percentage of patients, particularly in the first few months of therapy. TSH may not normalize due to a resetting of the pituitary-thyroid feedback threshold as a result of in utero hypothyroidism. Failure of the serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of TIROSINT therapy and/or of the serum TSH to decrease below 20 mU per L within 4 weeks should alert the physician to the possibility that the child is not receiving adequate therapy. Careful inquiry should then be made regarding compliance, dose of medication administered, and method of administration prior to increasing the dose of TIROSINT.
The recommended frequency of monitoring of TSH and total or FT4 in children is as follows: at 2 and 4 weeks after the initiation of treatment and following dose stabilization every 3 to 12 months thereafter until growth is completed. More frequent intervals of monitoring may be necessary if poor compliance is suspected or abnormal values are obtained. It is recommended that TSH and T4 levels, and a physical examination, if indicated, be performed 2 weeks after any change in TIROSINT dosage. Routine clinical examination, including assessment of mental and physical growth and development, and bone maturation, should be performed at regular intervals [See Warnings and Precautions (5.1), and Use in Specific Populations (8.4)].