Levothyroxine Dosage

Usual Adult Dose for Hypothyroidism

Oral:
The initial dose is 12.5 to 50 mcg orally once a day. The dosage can be increased in 12.5 to 25 mcg/day increments every 2 to 4 weeks. In older patients or in younger patients with a history of cardiovascular disease, the dosage should be increased in 12.5 to 25 mcg increments every 3 to 6 weeks.

Few patients require doses higher than 200 mcg. Inadequate response to doses higher than 200 mcg is rare and may suggest malabsorption, poor patient compliance and/or drug interactions.

Parenteral: The usual IV or IM dose is 50 to 75% of the oral dose.

Usual Adult Dose for TSH Suppression

Oral:
The initial dose is 50 mcg orally once a day. The dosage may be increased in 25 to 50 mcg increments every 2 to 4 weeks. The typical maintenance dose is 100 to 200 mcg orally once a day.

Parenteral: The usual IV or IM dose is 50 to 75 % of the oral dose.

Usual Adult Dose for Thyroid Suppression Test

Oral: 2.6 mcg/kg/day for 7 to 10 days.

Parenteral: The usual IV or IM dose is 50 to 75% of the oral dose.

Usual Adult Dose for Myxedema Coma

The initial dose 300 to 500 mcg IV bolus administered one time. The maintenance dose is 75 to 100 mcg IV once a day until the patient can be converted to oral therapy.

Usual Pediatric Dose for Hypothyroidism

Congenital hypothyroidism:
Neonatal:
Oral: 10 to 15 mcg/kg/day; if patient is at risk for development of cardiac failure, begin with a lower dose. In severe cases of hypothyroidism (T4 less than 5 mcg/dL), a higher initial dose of 12 to 17 mcg/kg/day may be considered.
IV or IM: 50% to 75% of the oral dose

Oral:
0 to 3 months: 10 to 15 mcg/kg orally once per day; if the infant is at risk for development of cardiac failure use a lower starting dose of approximately 25 mcg/day; if the initial serum T4 is very low (less than 5 mcg/dL) begin treatment at a higher dosage of approximately 50 mcg/day.

3 to 6 months: 8 to 10 mcg/kg or 25 to 50 mcg orally once per day

6 to 12 months: 6 to 8 mcg/kg or 50 to 75 mcg orally once per day

1 to 5 years: 5 to 6 mcg/kg or 75 to 100 mcg orally once per day

6 to 12 years: 4 to 5 mcg/kg or 100 to 125 mcg orally once per day

12 years: 2 to 3 mcg/kg or greater than or equal to 150 mcg orally once per day

Patients in which growth and puberty are complete: 1.7 mcg/kg orally once per day.

Note: Hyperactivity in older children may be minimized by starting at one-quarter of the recommended dose and increasing each week by that amount until the full dose is achieved (4 weeks).

For chronic or severe hypothyroidism:
Initial dose: 25 mcg orally once per day.

Increase dosage as needed in increments of 25 mcg every 2 to 4 weeks until the desired effect is achieved.

Parenteral:
The usual IV or IM dose is 50 to 75% of the oral dose.

Renal Dose Adjustments

Data not available

Liver Dose Adjustments

Data not available

Dose Adjustments

The sudden administration of large doses of levothyroxine in patients with concomitant heart disease is not without cardiovascular risks. The administration of a smaller initial dose may be appropriate.

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 attained.

In infants with very low (less than 5 mcg/dL) or undetectable serum T4 concentrations, the recommended initial starting dose is 50 mcg per day.

Precautions

Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children on levothyroxine therapy. Craniosynostosis in infants and premature closure of the epiphysis in children are risks with overtreatment, resulting in compromised adult height.

In adult patients with primary (thyroidal) hypothyroidism, serum TSH levels (using a sensitive assay) alone may be used to monitor treatment. Frequency of TSH monitoring during levothyroxine dosage titration depends on the clinical situation, but it is generally recommended at 6 to 8 week intervals until normalization. For patients who have recently initiated levothyroxine and whose serum TSH has normalized or in patients who have had their dosage or brand of levothyroxine changed, the serum TSH concentration should be assessed after 8 to 12 weeks. When the optimum replacement dosage has been attained, clinical (physical examination) and biochemical monitoring may be performed every 6 to 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 levothyroxine therapy.
In patients with congenital hypothyroidis, the adequacy of replacement therapy should be assessed by measuring both serum TSH (using a sensitive assay) and total or free T4. During the first three years of life, the serum total or free T4 should be maintained in the upper half of the normal range at all times. While the aim of treatment 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 treatment. 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 levothyroxine and/or of the serum TSH to decrease below 20 mU/L within 4 weeks should alert the prescriber to the possibility that the child is not receiving adequate treatment. Careful inquiry should then be made regarding compliance, dose of medication administered, and method of use prior to raising the dosage of levothyroxine.

The recommended frequency of monitoring of TSH and total or free T4 in children is as follows: at 2 and 4 weeks after the initiation of therapy; every 1 to 2 months during the first year of life; every 2 to 3 months between 1 and 3 years of age; and every 3 to 12 months thereafter until growth is completed. More frequent intervals of monitoring may be required if poor compliance is suspected or abnormal values are obtained. It is advised that TSH and T4 levels, and a physical examination, if indicated, be performed 2 weeks after any change in levothyroxine dosage. Routine clinical examination, including assessment of mental and physical growth and development, and bone maturation, should be conducted at regular intervals.

In pediatric patients with secondary (pituitary) and tertiary (hypothalamic) hypothyroidism, adequacy of treatment should be assessed by measuring serum free T4 levels, which should be maintained in the upper half of the normal range in these patients.

Dialysis

Very little drug is removed by dialysis because T4 is highly protein bound.

Other Comments

Levothyroxine should be administered as a single daily dose, preferably one-half to one hour before breakfast.

Levothyroxine should be taken at least 4 hours apart from drugs that are known to interfere with its absorption.

Levothyroxine tablets may be given to infants and children who cannot swallow whole tablets by crushing and suspending the freshly crushed tablet in a small amount of water (5 to 10 mL), breast milk, or non-soybean formula. The suspension should be prepared just prior to administration of the dose and should not be stored for any period of time. The crushed tablet can also be sprinkled over a small amount of food. Foods or formulas containing a large amount of soybean fiber or iron should not be used for administering levothyroxine.
Levothyroxine in capsule form should be swallowed whole and should not be opened, crushed or dissolved in liquid prior to administration.

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