Levothyroxine Dosage

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Usual Adult Dose for:

Usual Pediatric Dose for:

Additional dosage information:

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

Initial dose: 300 to 500 mcg IV bolus administered one time.
Maintenance dose: 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.

For chronic or severe hypothyroidism: 25 mcg orally once per day and increase dosage as needed in increments of 25 mcg every 2 to 4 weeks until the desired effect is achieved.

Comment:
- 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).
-The relative bioavailability between the injection and oral products has not been established. Therefore, caution should be used when switching patients from oral products to the injection as accurate dosing conversion has not been studied.
-A prospective randomized crossover study demonstrated that Synthroid and an AB-rated generic L-T4 are not bioequivalent for patients less than 3 years of age with severe congenital hypothyroidism.

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.

The relative bioavailability between the injection and oral products has not been established. Therefore, caution should be used when switching patients from oral products to the injection as accurate dosing conversion has not been studied.

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

Consult WARNINGS section for dosing related precautions.

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.

Reconstituted levothyroxine for injection is preservative free and stable for 4 hours. Any unused product should be discarded. Levothyroxine for injection should not be added to other intravenous fluids. The container closure is not made with natural rubber latex.

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