Brand names: Synthroid, Levothroid, Levoxyl, Unithroid
Levothyroxine, a synthetic thyroid hormone may be given in any of the following cases:
If your own thyroid gland is not making enough hormone;
If you have an enlarged thyroid (a goiter) or are at risk for developing a goiter;
If you have certain cancers of the thyroid;
If your thyroid production is low due to surgery, radiation, certain drugs, or disease of the pituitary gland or hypothalamus in the brain.
If you are taking levothyroxine to make up for a lack of natural hormone, it is important to take it regularly at the same time every day. You will probably need to take it for the rest of your life.
Take levothyroxine as a single dose, preferably on an empty stomach, one-half to one hour before breakfast. The drug is absorbed better on an empty stomach.
While taking levothyroxine, your doctor will perform periodic blood tests to determine whether you are getting the right amount.
--If you miss a dose...
Take it as soon as you remember. If it is almost time for your next dose, skip the one you missed and go back to your regular schedule. Never take 2 doses at the same time. If you miss 2 or more doses in a row, consult your doctor.
Keep levothyroxine in a tightly closed container. Store it at room temperature, away from light and moisture.
Side effects from levothyroxine, other than overdose symptoms, are rare. People who are treated with levothyroxine may initially lose some hair, but this effect is usually temporary. You may have an allergic reaction such as a rash or hives. Children may have an increase in pressure within the skull. Excessive dosage or a too rapid increase in dosage may lead to overstimulation of the thyroid gland. Notify your doctor immediately if you develop any if the following symptoms.
You should not be treated with levothyroxine if you are hypersensitive to thyroid hormone; your thyroid gland is making too much thyroid hormone; you have had a recent heart attack; or your adrenal glands are not making enough corticosteroid hormone.
Although levothyroxine will speed up your metabolism, it is not effective as a weight-loss drug and should not be used as such. An overdose may cause life-threatening side effects, especially if you take levothyroxine with an appetite-suppressant medication.
Levothyroxine has profound effects on the body. Make sure your doctor is aware of all your medical problems, especially heart disease, clotting disorders, diabetes, and disorders of the adrenal or pituitary glands. The doctor will also need to know about any allergies you may have to food or medicine, and will ask for the names of any medications you take, whether prescription or over-the-counter.
You should receive low doses of levothyroxine, under very close supervision, if you are an older person, or if you suffer from high blood pressure, angina (chest pain caused by a heart condition), or other types of heart disease. If you develop chest pain or additional circulatory problems, your dosage may have to be reduced.
If you have diabetes, or if your body makes insufficient adrenal corticosteroid hormone, levothyroxine will tend to make your symptoms worse. If you take medication for any of these disorders, the dosage will probably have to be adjusted once you begin taking levothyroxine. If diabetes is the problem, you should immediately report to your doctor any change in your glucose readings.
Postmenopausal women on long-term levothyroxine therapy may suffer a loss of bone density, increasing the danger of osteoporosis (brittle bones). To minimize the loss, the doctor will prescribe the lowest dosage needed to control symptoms of thyroid deficiency.
Levothyroxine may cause seizures at the beginning of treatment, although this is rare. You may also notice some hair loss at first, but this is temporary.
It may take a few weeks for levothyroxine to begin working, and you may not see any change in your symptoms until then.
Tell your doctor or dentist you are taking levothyroxine before you have surgery of any kind.
Tell your doctor if you become pregnant while you are taking levothyroxine. Your dose may need to be increased.
Do not switch to another brand of levothyroxine without consulting your doctor.
Excessive doses of levothyroxine in infants may cause the top of the skull to close too early. In children, overtreatment can stunt growth.
levothyroxine can interact with a wide variety of medications. It's advisable to check with your doctor before taking any other drug, but you should be especially wary of the following:Amiodarone (Cordarone)Androgens (male hormones)Antacids and anti-gas medicationsAntidepressants such as Elavil, Ludiomil, and ZoloftBlood pressure drugs such as beta blockers, nitroprusside, and thiazide diureticsBlood-thinning drugs such as Coumadin and heparinChloral hydrate (a sedative)Diabetes drugs such as insulin and MicronaseDigitalis-type drugs such as LanoxinEstrogen products and oral contraceptivesFurosemide (Lasix)Growth hormonesHormone inhibitors such as Cytadren and TapazoleIodideIron supplementsKayexalateKetamine (Ketalar)Lithium (Eskalith, Lithobid)Methadone and heroinMetoclopramide (Reglan)Nonsteroidal anti-inflammatory drugs such as phenylbutazone and aspirinParkinson's drugs such as SinemetPropylthiouracil (a thyroid inhibitor)Seizure medications such as Dilantin, Tegretol, and phenobarbitalSteroids such as dexamethasone and hydrocortisoneStimulants such as epinephrine (EpiPen)Sucralfate (Carafate)The cancer drugs 5-fluorouracil, 6-mercaptopurine, mitotane, and tamoxifenThe cholesterol-lowering drugs Colestid, Mevacor, and QuestranThe immune-system drugs interferon and interleukinThe tranquilizers Trilafon and ValiumThe tuberculosis drugs aminosalicylate, rifampin, and ethionamideTheophylline (Theo-Dur)
A high-fiber diet, soy-containing supplements, and walnuts can also interfere with levothyroxine effects.
If you need to take levothyroxine because of a thyroid hormone deficiency, you can continue to take levothyroxine during pregnancy. In fact, your doctor will test you regularly and may increase your dose. Once your baby is born, you may breastfeed while continuing to take carefully regulated doses of levothyroxine.
Your doctor will tailor the dosage to meet your individual requirements, taking into consideration the status of your thyroid gland and other medical conditions you may have. Older adults often require somewhat smaller doses. To make sure the dosage is right for you, the doctor will monitor your thyroid hormone level with periodic blood tests.
An overdose of levothyroxine can produce the same symptoms of overstimulation listed under "levothyroxine side effects" Confusion and disorientation are also possible, and there have been reports of stroke, shock, coma, and death. If you suspect a massive overdose, seek emergency medical attention immediately.