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Levothyroxine Dosage

Applies to the following strength(s): 25 mcg (0.025 mg) ; 50 mcg (0.05 mg) ; 75 mcg (0.075 mg) ; 100 mcg (0.1 mg) ; 125 mcg (0.125 mg) ; 150 mcg (0.15 mg) ; 200 mcg (0.2 mg) ; 300 mcg (0.3 mg) ; 500 mcg (0.5 mg) ; 88 mcg (0.088 mg) ; 112 mcg (0.112 mg) ; 175 mcg (0.175 mg) ; 137 mcg (0.137 mg) ; 13 mcg (0.013 mg)

The information at Drugs.com is not a substitute for medical advice. ALWAYS consult your doctor or pharmacist.

Usual Adult Dose for:

Usual Geriatric Dose for:

Usual Pediatric Dose for:

Additional dosage information:

Usual Adult Dose for Hypothyroidism

-HYPOTHYROIDISM IN ADULTS AND IN CHILDREN IN WHOM GROWTH AND PUBERTY ARE COMPLETE:
Therapy may begin at full replacement doses in otherwise healthy individuals less than 50 years old and in those older than 50 years who have been recently treated for hyperthyroidism or who have been hypothyroid for only a short time (such as a few months):
Average full replacement dose: 1.7 mcg/kg/day (e.g., 100 to 125 mcg/day for a 70 kg adult) orally
Older patients may require less than 1 mcg/kg/day
Doses greater than 200 mcg/day orally are seldom required
An inadequate response to oral daily doses of 300 mcg/day or greater is rare and may indicate poor compliance, malabsorption, and/or drug interactions
-FOR MOST PATIENTS OLDER THAN 50 YEARS OR FOR PATIENTS UNDER 50 YEARS OF AGE WITH UNDERLYING CARDIAC DISEASE:
-Initial dose: 25 to 50 mcg/day, with gradual increments in dose at 6 to 8 week intervals, as needed
-PATIENTS WITH SEVERE HYPOTHYROIDISM:
-Initial dose: 12.5 to 50 mcg orally once a day; dosage can be increased in 12.5 to 25 mcg/day increments every 2 to 4 weeks (accompanied by clinical and laboratory assessment, until the TSH level is normalized)
-PATIENTS WITH SECONDARY (PITUITARY) OR TERTIARY (HYPOTHALAMIC) HYPOTHYROIDISM: The oral dose should be titrated until the patient is clinically euthyroid and the serum free-T4 level is restored to the upper half of the normal range

Comments:
-The dose should be individualized on the basis of clinical response and biochemical tests. Regular monitoring of TSH and thyroxine is recommended when starting therapy or changing the dose.
-This drug should be taken in the morning on an empty stomach with water, at least one-half hour before any food is eaten.
-This drug should be taken at least 4 hours apart from drugs that are known to interfere with its absorption.
-The peak therapeutic effect of this drug may not be attained for 4 to 6 weeks.

Use: As 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 and subclinical hypothyroidism. Primary hypothyroidism may result from functional deficiency, primary atrophy, partial or total congenital absence of the thyroid gland, or from the effects of surgery, radiation, or drugs, with or without the presence of goiter.

Usual Adult Dose for TSH Suppression

TSH SUPPRESSION IN WELL-DIFFERENTIATED THYROID CANCER AND THYROID NODULES:
-The target level for TSH suppression in these conditions has not been established. The efficacy of TSH suppression for benign nodular disease is controversial. Therefore, the dose of this drug used for TSH suppression should be individualized based on the specific disease and the patient being treated.
-In the treatment of well differentiated (papillary and follicular) thyroid cancer, this drug is used as an adjunct to surgery and radioiodine therapy. Generally, TSH is suppressed to less than 0.1 international units per liter (mU/L), and this usually requires a dose of greater than 2 mcg/kg/day. However, in patients with high-risk tumors, the target level for TSH suppression may be less than 0.01 mU/L.
-In the treatment of benign nodules and nontoxic multinodular goiter, TSH is generally suppressed to a higher target (e.g., 0.1 to 0.5 mU/L for nodules and 0.5 to 1.0 mU/L for multinodular goiter) than that used for the treatment of thyroid cancer. This drug is contraindicated if the serum TSH is already suppressed due to the risk of precipitating overt thyrotoxicosis.

Usual Adult Dose for Myxedema Coma

Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism, and may result in unpredictable absorption of the oral dosage form of this drug from the GI. Only the IV dosage form should be used for this condition:
IV:
-Initial loading dose: 300 to 500 mcg IV
-Maintenance dose: 50 and 100 mcg IV, until the patient can tolerate oral therapy

Comment:
-The age, general physical condition, cardiac risk factors, and severity of myxedema and duration of myxedema symptoms should be considered when determining the starting and maintenance dosages.

Use: Myxedema coma

Usual Geriatric Dose for Hypothyroidism

ELDERLY PATIENTS WITH CARDIAC DISEASE:
-Initial dose: 12.5 to 25 mcg orally per day, with gradual dose increments at 4 to 6 week intervals
-The dose is generally adjusted in 12.5 to 25 mcg increments until the patient with primary hypothyroidism is clinically euthyroid and the serum TSH has normalized.

Comments:
-The dose should be individualized on the basis of clinical response and biochemical tests. Regular monitoring of TSH and thyroxine is recommended when starting therapy or changing the dose.
-This drug should be taken in the morning on an empty stomach with water, at least one-half hour before any food is eaten.
-This drug should be taken at least 4 hours apart from drugs that are known to interfere with its absorption.
-The peak therapeutic effect of this drug may not be attained for 4 to 6 weeks.

Usual Pediatric Dose for Hypothyroidism

CONGENITAL OR ACQUIRED HYPOTHYROIDISM:
-Neonatal: 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.
-Age 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 per day; if the initial serum T4 is very low (less than 5 mcg/dL) begin treatment at a higher dosage of approximately 50 mcg per day
-Age 3 to 6 months: 8 to 10 mcg/kg/day
-Age 6 to 12 months: 6 to 8 mcg/kg/day
-Age 1 to 5 years: 5 to 6 mcg/kg/day
-Age 6 to 12 years: 4 to 5 mcg/kg/day
-Age 12 years and older: 2 to 3 mcg/kg/day
-Patients in which growth and puberty are complete: 1.7 mcg/kg/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.

Comments:
-Therapy should be instituted at full replacement doses as soon as possible.
-Delays in diagnosis and institution of therapy may have deleterious effects on intellectual and physical growth and development.
-Undertreatment and overtreatment should be avoided
-For infants and children who cannot swallow intact tablets, the tablet may be crushed and suspended in 5 to 10 mL or 1 to 2 teaspoonfuls of water. This suspension can be administered by spoon or dropper.
-Foods that decrease absorption of this drug, such as soybean infant formula, should not be used for administering this drug.
-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).

Renal Dose Adjustments

No adjustment recommended. Thyroid function tests may be influenced by renal impairment.

Liver Dose Adjustments

No adjustment recommended. Thyroid function tests may be influenced by liver impairment.

Dose Adjustments

-Caution is required when initiating this drug in elderly patients, patients with coronary heart disease, and in patients with severe or long-existing hypothyroidism. An initial low dose is recommended, which should be increased slowly and using longer intervals.
-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.
-Pregnancy may increase levothyroxine requirements.

Precautions

US BOXED WARNING:
Thyroid hormones, either alone or with other agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

Consult WARNINGS section for additional precautions.

Dialysis

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

Other Comments

Administration advice:
-This drug should be administered as a single daily dose, preferably one-half to one hour before breakfast with water.
-This drug should be taken at least 4 hours apart from drugs that are known to interfere with its absorption.
-This drug may be administered to infants and children who cannot swallow intact tablets by crushing the tablet and suspending the freshly crushed tablet in a small amount (5 to 10 mL or 1 to 2 teaspoonfuls) of water.
-Foods that decrease absorption of this drug, such as soybean infant formula, should not be used for administering the tablets.
-This drug should not be used as a primary or adjunctive therapy in a weight control program
-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

Monitoring:
-Patients switching from the tablet formulation to the liquid formulation and vice versa should be monitored closely.

Patient advice:
-Take this drug in the morning on an empty stomach, at least one-half hour before eating any food.
-The tablet may rapidly swell and disintegrate resulting in choking, gagging, the tablet getting stuck in your throat or difficulty swallowing. It is very important that you take the tablet with a full glass of water.
-It may take several weeks before you notice an improvement in your symptoms.
-Notify your physician if you experience any of the following symptoms: rapid or irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives or skin rash, or any other unusual medical event.
-Notify your physician if you become pregnant while taking this drug.
-Notify your physician or dentist that you are taking this drug prior to any surgery.
-Partial hair loss may occur rarely during the first few months of therapy, but this is usually temporary.

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