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levothyroxine

Pronunciation

Generic Name: levothyroxine (LEE voe thye ROX een)
Brand Name: Levothroid, Levoxyl, Synthroid, Tirosint, Unithroid, ...show all 16 brand names

What is levothyroxine?

Levothyroxine is a replacement for a hormone normally produced by your thyroid gland to regulate the body's energy and metabolism. Levothyroxine is given when the thyroid does not produce enough of this hormone on its own.

Levothyroxine treats hypothyroidism (low thyroid hormone). Levothyroxine is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

Levothyroxine may also be used for purposes not listed in this medication guide.

What is the most important information I should know about levothyroxine?

You may not be able to take this medication if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder, a thyroid disorder called thyrotoxicosis, or if you have any recent or current symptoms of a heart attack.

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants.

What should I discuss with my healthcare provider before taking levothyroxine?

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants.

Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. However, you may not be able to take this medication if you have certain medical conditions.

To make sure levothyroxine is safe for you, tell your doctor if you have:

  • a thyroid disorder called thyrotoxicosis;

  • heart disease, coronary artery disease, or a history of blood clots;

  • diabetes (insulin or oral diabetes medication doses may need to be changed when you start taking levothyroxine);

  • anemia (lack of red blood cells);

  • osteoporosis, or low bone mineral density;

  • problems with your pituitary gland;

  • any food or drug allergies;

  • an untreated or uncontrolled adrenal gland disorder; or

  • if you have recently had a heart attack, or are having any symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the jaw or shoulder, nausea, sweating, general ill feeling).

Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).

FDA pregnancy category A. Levothyroxine is not expected to harm an unborn baby. If you become pregnant while taking levothyroxine, do not stop taking the medicine without your doctor's advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Your dose needs may be different during pregnancy.

Levothyroxine can pass into breast milk, but it is not expected to be harmful to a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby. Your dose needs may be different while you are nursing.

How should I take levothyroxine?

Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Do not share this medication with another person, even if they have the same symptoms you have.

Levothyroxine works best if you take it on an empty stomach, at least 30 minutes before breakfast. Follow your doctor's dosing instructions and try to take the medicine at the same time each day.

It is very important to take Levoxyl with a full glass (8 ounces) of water. The Levoxyl tablet can dissolve very quickly and swell in the throat, possibly causing choking or gagging.

While using levothyroxine, you may need frequent medical tests.

Tell any doctor or dentist who treats you that you are using levothyroxine.

Store at room temperature away from moisture and heat.

It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well. You may need to use levothyroxine for the rest of your life to replace the thyroid hormone your body cannot produce.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include headache, leg cramps, tremors, feeling nervous or irritable, chest pain, shortness of breath, and fast or pounding heartbeats.

What should I avoid while taking levothyroxine?

Certain medicines can make levothyroxine less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take levothyroxine:

  • calcium carbonate (Alka-Mints, Calcium Oyster Shell, Caltrate, Os-Cal, Oyster Shell Calcium, Rolaids Soft Chew, Tums, and others);

  • cholestyramine, colestipol;

  • ferrous sulfate iron supplement;

  • sucralfate;

  • sodium polystyrene sulfonate (Kalexate, Kayexalate, Kionex); or

  • antacids that contain aluminum or magnesium--Acid Gone, Gaviscon, Maalox, Milk of Magnesia, Mintox, Mylanta, Pepcid Complete, and others).

Avoid the following food products, which can make your body absorb less levothyroxine: infant soy formula, cotton seed meal, walnuts, and high-fiber foods.

Levothyroxine side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

  • fast or irregular heart rate;

  • fever, hot flashes, sweating;

  • sleep problems (insomnia);

  • changes in your menstrual periods; or

  • vomiting, diarrhea, appetite changes, weight changes.

Common side effects may include mild hair loss.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

Levothyroxine dosing 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).

What other drugs will affect levothyroxine?

Many other medicines can be affected by your thyroid hormone levels. Other medicine may also increase or decrease the effects of levothyroxine.

Many drugs can interact with levothyroxine and not all possible interactions are listed in this medication guide.

Tell your doctor about all medications you use, start using, or stop using during your treatment with levothyroxine. This includes prescription, over-the-counter, vitamin, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.

Where can I get more information?

  • Your pharmacist can provide more information about levothyroxine.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
  • Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2012 Cerner Multum, Inc. Version: 11.03. Revision Date: 2014-09-14, 6:08:51 PM.

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