Patient Education
Do not use methimazole if you are pregnant. It could harm the unborn baby. Do not take methimazole if you are breast-feeding a baby. Methimazole can increase your risk of bleeding. If you need to have surgery, tell the surgeon ahead of time that you are using this medication. Methimazole can lower blood cells that help your body fight infections. This can make it easier for you to bleed from an injury or get sick from being around others who are ill. Your blood may need to be tested often. Visit your doctor regularly. Do not receive a "live" vaccine while you are being treated with methimazole, and avoid coming into contact with anyone who has recently received a live vaccine. There is a chance that the virus could be passed on to you. Keep using this medication even if you feel fine or have no symptoms of hyperthyroidism. You may need to keep taking methimazole long term to control your condition. Stopping the medication could cause your symptoms to return. What is methimazole? Methimazole prevents the thyroid gland from producing too much thyroid hormone. Methimazole is used to treat hyperthyroidism (overactive thyroid). It is also used before thyroid surgery or radioactive iodine treatment. Methimazole may also be used for other purposes not listed in this medication guide. What should I discuss with my healthcare provider before taking methimazole? Do not use this medication if you are allergic to methimazole. If you have any of these other conditions, you may need a dose adjustment or special tests to safely take this medication:
Methimazole can pass into breast milk and may harm a nursing baby. Do not use methimazole if you are breast-feeding a baby. How should I take methimazole? Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label. Take methimazole with a full glass of water. Methimazole can be taken with or without food, but you should take it the same way each time. Methimazole can increase your risk of bleeding. If you need to have any type of surgery, tell the surgeon ahead of time that you are using this medication. Methimazole can lower blood cells that help your body fight infections. This can make it easier for you to bleed from an injury or get sick from being around others who are ill. Your blood may need to be tested often. Visit your doctor regularly. It is important to use methimazole regularly to get the most benefit. Get your prescription refilled before you run out of medicine completely. Keep using this medication even if you feel fine or have no symptoms of hyperthyroidism. You may need to keep taking methimazole long term to control your condition. Stopping the medication could cause your symptoms to return. Store at room temperature away from moisture and heat. 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 nausea, vomiting, upset stomach, headache, joint pain, fever, itching, swelling, or pale skin and easy bruising or bleeding. What should I avoid while taking methimazole? Avoid being near people who are sick or have infections. Tell your doctor at once if you develop signs of infection. Do not receive a "live" vaccine while using methimazole, and avoid coming into contact with anyone who has recently received a live vaccine. There is a chance that the virus could be passed on to you. Live vaccines include measles, mumps, rubella (MMR), oral polio, chickenpox (varicella), BCG (Bacillus Calmette and Guérin), and nasal flu vaccine. What are the possible side effects of methimazole? Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Stop using methimazole and call your doctor at once if you have a serious side effect such as:
What other drugs will affect methimazole?Tell your doctor about all other medicines you use, especially:
Where can I get more information?Your pharmacist can provide more information about methimazole. 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. 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. |
Patient Education - Spanish
No use methimazole si usted está embarazada. Le puede causar daño al bebé nonato. No tome methimazole si le está dando de lactar al bebé. Methimazole puede aumentar su riesgo a sangrar. Si necesita someterse a una cirugía, dígale al cirujano con anticipación que usted está usando esta medicina. Methimazole puede disminuir las células de la sangre que ayudan a su cuerpo a combatir infecciones. Esto puede hacer para usted más fácil sangrar de una herida o enfermarse por estar alrededor de otros que están enfermos. Su sangre puede necesitar ser examinada con frecuencia. Visite a su médico con regularidad. No reciba una vacuna "viva" mientras esté recibiendo tratamiento con methimazole, y evite contacto con las personas que han recibido una vacuna con células vivas. Existe la posibilidad que le pasen el virus a usted. Siga usando esta medicina aun cuando se sienta bien o no note los síntomas del hipertiroidismo. Usted tal vez necesite tomar methimazole por largo tiempo para controlar su condición. Dejar de usar la medicina podría causar que sus síntomas vuelvan. ¿Qué es methimazole? Methimazole impide que la glándula tiroidea produzca demasiado hormona tiroidea. Methimazole se usa en el tratamiento de hipertiroidismo (tiroides sobre activa). También se usa antes de la cirugía de la tiroides o el tratamiento de radiación con yodo de la tiroides. Methimazole también puede ser usada para fines diferentes a los mencionados en esta guía del medicamento. ¿Qué debería discutir con el profesional del cuidado de la salud antes de tomar methimazole? No use esta medicina si tiene alergia a methimazole. Si usted tiene cualquiera de estas otras condiciones, quizás necesite modificar su dosis o pruebas especiales para que pueda usar esta medicina con seguridad:
Methimazole puede pasar a la leche materna y le puede hacer daño al bebé lactante. No use methimazole si le está dando de lactar al bebé. ¿Cómo debo tomar methimazole? Tómelo exactamente cómo lo haya recetado su médico. No lo tome en cantidades mayores o menores, o por más tiempo de lo recomendado. Siga las instrucciones en la etiqueta de su prescripción. Tome methimazole con un vaso de agua lleno. Methimazole puede tomar se con o sin comida, pero la debe tomar de la misma forma cuando la tome. Methimazole puede aumentar su riesgo de sangrar. Si necesita someterse a una cirugía, dígale al cirujano con anticipación que usted está usando esta medicina.. Methimazole puede disminuir las células de la sangre que ayudan a su cuerpo a combatir infecciones. Esto puede hacer para usted más fácil sangrar de una herida o enfermarse por estar alrededor de otros que están enfermos. Su sangre puede necesitar ser examinada con frecuencia. Visite a su médico con regularidad. Usar methimazole regularmente para obtener el mayor beneficio. Vuelva a llenar su prescripción antes de que se quede completamente sin medicina. Siga usando esta medicina aun cuando se sienta bien o no note los síntomas del hipertiroidismo. Usted tal vez necesite tomar methimazole por largo tiempo para controlar su condición. Dejar de usar la medicina podría causar que sus síntomas vuelvan. Guarde methimazole a temperatura ambiental lejos de la humedad y calor. ¿Qué sucede si me salto una dosis?Tome la dosis pasada tan pronto se acuerde. Sáltese la dosis pasada si ya casi es hora para la siguiente dosis. No tome más medicina para alcanzar la dosis pasada. ¿Qué sucedería en una sobredosis? Busque atención médica de emergencia o llame a la línea de Poison Help al 1-800-222-1222. Los síntomas de una sobredosis de methimazole pueden incluir náusea, vómito, malestar estomacal, dolor de cabeza, dolor de las articulaciones, fiebre, picazón, hinchazón, o piel pálida y sangrar con facilidad o moretones.. ¿Qué debo evitar mientras uso methimazole?Evite estar en contacto con personas enfermas o que tengan infecciones. Hable con su médico de inmediato si usted desarrolla síntomas de infección. No reciba una vacuna "viva" mientras usa methimazole, y evite el contacto con gente que ha recibido recientemente una vacuna viva. Existe la posibilidad de que le pasen el virus. Las vacunas vivas incluyen sarampión, paperas, rubéola (MMR), polio oral, varicela, BCG (Bacillus Calmette and Guérin), y la vacuna de gripe nasal. ¿Cuáles son los efectos secundarios posibles de methimazole? Busque atención médica de emergencia si usted nota alguno de estos síntomas de una reacción alérgica: ronchas; dificultad para respirar; hinchazón de la cara, labios, lengua, o garganta. Deje de usar methimazole y llame a su médico de inmediato si usted tiene un efecto secundario grave como:
¿Qué otras drogas afectarán a methimazole?Dígale a su médico acerca de todas las medicinas que usted use, especialmente:
¿Dónde puedo obtener más información?Su farmacéutico le puede dar más información acerca de methimazole. Recuerde, mantenga ésta y todas las otras medicinas fuera del alcance de los niños, no comparta nunca sus medicinas con otros, y use este medicamento sólo para la condición por la que fue recetada. 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. 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. |
Antithyroid drugs may be used:
●As a short-term treatment in people with Graves' hyperthyroidism, to prepare for thyroid surgery or radioiodine.
●As initial treatment in Graves' disease for one to two years to see if the disease resolves. Approximately 30 percent of people with Graves' disease will have a remission after treatment for one to two years with antithyroid drugs.
●To treat hyperthyroidism associated with toxic multinodular goiter or a toxic adenoma ("hot nodule"), usually to prepare for thyroid surgery or radioiodine. (See "Patient education: Thyroid nodules (Beyond the Basics)".)
●To treat women with hyperthyroidism during pregnancy.
●For long-term treatment of hyperthyroidism due to Graves' disease or toxic multinodular goiter or toxic adenoma when patients prefer to avoid definitive therapy with radioiodine or surgery.
You will need to take antithyroid drugs for at least three weeks (usually six to eight weeks or longer) to lower thyroid hormone levels. This is because they only block formation of new thyroid hormone; they do not remove thyroid hormones that are already in the thyroid and the blood stream. If you frequently miss taking the antithyroid drug, thyroid hormone synthesis may resume quickly and replenish thyroid gland stores, prolonging or preventing adequate control of the hyperthyroidism.
TYPES OF ANTITHYROID DRUGS Two antithyroid drugs are currently available in the United States: propylthiouracil and methimazole (brand name: Tapazole). Carbimazole (which is converted into methimazole in the body) is available in Europe and parts of Asia but not in the United States.
Methimazole — Methimazole is usually preferred over propylthiouracil because it reverses hyperthyroidism more quickly and has fewer side effects. Methimazole requires an average of six weeks to lower T4 levels to normal and is often given before radioactive iodine treatment. Methimazole can be taken once per day.
Propylthiouracil — Propylthiouracil does not reverse hyperthyroidism as rapidly as methimazole, and it has more side effects. Because of its potential for liver damage, it is used only when methimazole or carbimazole are not appropriate. Propylthiouracil must be taken two to three times per the day.
Antithyroid drugs during pregnancy — Propylthiouracil is the drug of choice during the first trimester of pregnancy because it causes less severe birth defects than methimazole. Because there have been rare cases of liver damage in people taking propylthiouracil, some clinicians will suggest switching to methimazole after the first trimester, while others may continue propylthiouracil.
For women who are nursing, methimazole is probably a better choice than propylthiouracil (to avoid liver side effects).
If you take antithyroid drugs, you should discuss your treatment with your doctor before becoming pregnant. Having radioiodine treatment or surgery at least six months before becoming pregnant can eliminate the need for antithyroid treatment during pregnancy.
Antithyroid drug side effects — Most of the side effects of antithyroid drugs are minor, but major side effects can occur. Because there is no way to predict who will experience side effects, it is important to discuss all possible side effects before starting treatment.
If you cannot tolerate antithyroid treatments, you can consider radioiodine treatment or surgery.
Minor side effects — Up to 15 percent of people who take an antithyroid drug have minor side effects. Both methimazole and propylthiouracil can cause itching, rash, hives, joint pain and swelling, fever, changes in taste, nausea, and vomiting.
If one antithyroid drug causes side effects, switching to the other drug may be helpful. However, approximately one-half of people who have side effects with one drug will have similar side effects with the other. Nausea and vomiting may depend on the dose; spreading large doses out through the day can reduce side effects.
Major side effects — Fortunately, the major side effects of antithyroid drugs are very rare.
●Agranulocytosis – Agranulocytosis is a term used to describe a severe decrease in the production of white blood cells. This condition is extremely serious but affects only 1 out of every 200 to 500 people who take an antithyroid drug. Older people taking propylthiouracil and those who take high doses of methimazole may be at higher risk of this side effect.
Agranulocytosis more commonly occurs within the first three months of starting treatment with an antithyroid drug but rarely can occur later. If you develop a sore throat, fever, or other signs or symptoms of infection, you should stop your medicine and immediately call your doctor or nurse to have a complete blood count (CBC). Serious and potentially life-threatening infections, or even death, can occur before agranulocytosis resolves. However, once the antithyroid drug is stopped, agranulocytosis usually resolves within a week.
●Other – There are three other very rare complications of antithyroid drugs: liver damage (more common with propylthiouracil), aplastic anemia (failure of the bone marrow to produce blood cells), and vasculitis (inflammation of blood vessels associated with propylthiouracil).
Propylthiouracil-related liver damage typically occurs within three months of starting the drug. If you develop jaundice, dark urine, light stools, abdominal pain, loss of appetite, nausea, or other evidence of liver dysfunction, you should discontinue the drug immediately and contact your clinician for assessment of liver function. Propylthiouracil-related liver failure can be serious and potentially life threatening.
The risk of liver damage from propylthiouracil is an important concern, particularly in children. For this reason, methimazole is the first choice for treating hyperthyroidism.
MONITORING THYROID HORMONES DURING TREATMENTDuring treatment, your blood thyroid hormone levels will be monitored periodically. Antithyroid drugs typically reduce levels of both triiodothyronine (T3) and thyroxine (T4), but levels of T3 may take longer to return to normal. Thyroid-stimulating hormone (TSH) levels usually take the longest to return to normal.
Approximately 30 percent of people who take an antithyroid drug for one to two years will have prolonged remission of Graves' disease. It is not known if the antithyroid drug plays an active role in this remission or if it simply controls thyroid hormone levels until Graves' disease resolves on its own.
Checking for remission and recurrence — No test can reliably predict remission of Graves' disease. While imperfect, the measurement of TSH-receptor antibodies (TRAb) is widely used in the United States and Europe to determine if a person is in remission.
Usually, after one to two years of treatment, TRAb is measured, and if low, your clinician will recommend stopping the antithyroid drug, and the chance of a remission is 80 percent. However, if TRAb remains high, the chance of a remission is under 20 percent, and it is appropriate to reconsider definitive therapy with radioiodine or surgery or continue antithyroid drugs.
If antithyroid drugs are stopped, thyroid blood tests are usually performed four to eight weeks later. The blood tests are periodically repeated over 12 months to determine if hormone levels remain normal or increase over time (this is called a recurrence).
If your levels of T3, T4, and TSH remain normal for 12 months, the long-term prognosis is good. Recurrence after this time occurs in only 8 to 10 percent of people.
●As a short-term treatment in people with Graves' hyperthyroidism, to prepare for thyroid surgery or radioiodine.
●As initial treatment in Graves' disease for one to two years to see if the disease resolves. Approximately 30 percent of people with Graves' disease will have a remission after treatment for one to two years with antithyroid drugs.
●To treat hyperthyroidism associated with toxic multinodular goiter or a toxic adenoma ("hot nodule"), usually to prepare for thyroid surgery or radioiodine. (See "Patient education: Thyroid nodules (Beyond the Basics)".)
●To treat women with hyperthyroidism during pregnancy.
●For long-term treatment of hyperthyroidism due to Graves' disease or toxic multinodular goiter or toxic adenoma when patients prefer to avoid definitive therapy with radioiodine or surgery.
You will need to take antithyroid drugs for at least three weeks (usually six to eight weeks or longer) to lower thyroid hormone levels. This is because they only block formation of new thyroid hormone; they do not remove thyroid hormones that are already in the thyroid and the blood stream. If you frequently miss taking the antithyroid drug, thyroid hormone synthesis may resume quickly and replenish thyroid gland stores, prolonging or preventing adequate control of the hyperthyroidism.
TYPES OF ANTITHYROID DRUGS Two antithyroid drugs are currently available in the United States: propylthiouracil and methimazole (brand name: Tapazole). Carbimazole (which is converted into methimazole in the body) is available in Europe and parts of Asia but not in the United States.
Methimazole — Methimazole is usually preferred over propylthiouracil because it reverses hyperthyroidism more quickly and has fewer side effects. Methimazole requires an average of six weeks to lower T4 levels to normal and is often given before radioactive iodine treatment. Methimazole can be taken once per day.
Propylthiouracil — Propylthiouracil does not reverse hyperthyroidism as rapidly as methimazole, and it has more side effects. Because of its potential for liver damage, it is used only when methimazole or carbimazole are not appropriate. Propylthiouracil must be taken two to three times per the day.
Antithyroid drugs during pregnancy — Propylthiouracil is the drug of choice during the first trimester of pregnancy because it causes less severe birth defects than methimazole. Because there have been rare cases of liver damage in people taking propylthiouracil, some clinicians will suggest switching to methimazole after the first trimester, while others may continue propylthiouracil.
For women who are nursing, methimazole is probably a better choice than propylthiouracil (to avoid liver side effects).
If you take antithyroid drugs, you should discuss your treatment with your doctor before becoming pregnant. Having radioiodine treatment or surgery at least six months before becoming pregnant can eliminate the need for antithyroid treatment during pregnancy.
Antithyroid drug side effects — Most of the side effects of antithyroid drugs are minor, but major side effects can occur. Because there is no way to predict who will experience side effects, it is important to discuss all possible side effects before starting treatment.
If you cannot tolerate antithyroid treatments, you can consider radioiodine treatment or surgery.
Minor side effects — Up to 15 percent of people who take an antithyroid drug have minor side effects. Both methimazole and propylthiouracil can cause itching, rash, hives, joint pain and swelling, fever, changes in taste, nausea, and vomiting.
If one antithyroid drug causes side effects, switching to the other drug may be helpful. However, approximately one-half of people who have side effects with one drug will have similar side effects with the other. Nausea and vomiting may depend on the dose; spreading large doses out through the day can reduce side effects.
Major side effects — Fortunately, the major side effects of antithyroid drugs are very rare.
●Agranulocytosis – Agranulocytosis is a term used to describe a severe decrease in the production of white blood cells. This condition is extremely serious but affects only 1 out of every 200 to 500 people who take an antithyroid drug. Older people taking propylthiouracil and those who take high doses of methimazole may be at higher risk of this side effect.
Agranulocytosis more commonly occurs within the first three months of starting treatment with an antithyroid drug but rarely can occur later. If you develop a sore throat, fever, or other signs or symptoms of infection, you should stop your medicine and immediately call your doctor or nurse to have a complete blood count (CBC). Serious and potentially life-threatening infections, or even death, can occur before agranulocytosis resolves. However, once the antithyroid drug is stopped, agranulocytosis usually resolves within a week.
●Other – There are three other very rare complications of antithyroid drugs: liver damage (more common with propylthiouracil), aplastic anemia (failure of the bone marrow to produce blood cells), and vasculitis (inflammation of blood vessels associated with propylthiouracil).
Propylthiouracil-related liver damage typically occurs within three months of starting the drug. If you develop jaundice, dark urine, light stools, abdominal pain, loss of appetite, nausea, or other evidence of liver dysfunction, you should discontinue the drug immediately and contact your clinician for assessment of liver function. Propylthiouracil-related liver failure can be serious and potentially life threatening.
The risk of liver damage from propylthiouracil is an important concern, particularly in children. For this reason, methimazole is the first choice for treating hyperthyroidism.
MONITORING THYROID HORMONES DURING TREATMENTDuring treatment, your blood thyroid hormone levels will be monitored periodically. Antithyroid drugs typically reduce levels of both triiodothyronine (T3) and thyroxine (T4), but levels of T3 may take longer to return to normal. Thyroid-stimulating hormone (TSH) levels usually take the longest to return to normal.
Approximately 30 percent of people who take an antithyroid drug for one to two years will have prolonged remission of Graves' disease. It is not known if the antithyroid drug plays an active role in this remission or if it simply controls thyroid hormone levels until Graves' disease resolves on its own.
Checking for remission and recurrence — No test can reliably predict remission of Graves' disease. While imperfect, the measurement of TSH-receptor antibodies (TRAb) is widely used in the United States and Europe to determine if a person is in remission.
Usually, after one to two years of treatment, TRAb is measured, and if low, your clinician will recommend stopping the antithyroid drug, and the chance of a remission is 80 percent. However, if TRAb remains high, the chance of a remission is under 20 percent, and it is appropriate to reconsider definitive therapy with radioiodine or surgery or continue antithyroid drugs.
If antithyroid drugs are stopped, thyroid blood tests are usually performed four to eight weeks later. The blood tests are periodically repeated over 12 months to determine if hormone levels remain normal or increase over time (this is called a recurrence).
If your levels of T3, T4, and TSH remain normal for 12 months, the long-term prognosis is good. Recurrence after this time occurs in only 8 to 10 percent of people.