Tapazole

Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule at evenly spaced, 8-hour intervals. Do not take a double dose to make up for a missed one.

Methimazole is the generic name for Tapazole, a prescription drug used to treat an overactive thyroid.

An overactive thyroid can be caused by conditions like Graves' disease, inflammation of the thyroid gland, or Plummer's disease.

Tapazole belongs to a group of drugs known as anti-thyroid agents. It works by interfering with the production of thyroid hormones — an action that decreases levels of these hormones in the body.

The Food and Drug Administration (FDA) first approved methimazole under the brand name Tapazole in 1950. It was originally manufactured by King Pharmaceuticals.

Methimazole Warnings

Don't take methimazole if you're allergic to the drug or any of its ingredients.

Women should avoid taking methimazole while breastfeeding.

Talk to your doctor before taking methimazole if you:

• Are pregnant
• Have low counts of red blood cells, white blood cells, or platelets
• Are taking Clozaril (clozapine) or Propyl-Thyracil (propylthiouracil, or PTU)
• Are receiving radiation treatment

Pregnancy and Methimazole

Studies show that methimazole may cause birth defects.

Manufacturers of the drug state that it's not safe to take during pregnancy.

But your doctor may feel that the benefits of taking the drug during pregnancy outweigh the risks in certain situations.

Methimazole is passed into breast milk, and its safety for nursing babies has been a topic of debate. Talk to your doctor before taking the drug while breastfeeding.

It's always a good idea to talk to your doctor about all medications you're taking if you're pregnant, planning a pregnancy, or breastfeeding.

Methimazole for Cats

Veterinarians prescribe methimazole for overactive thyroids in cats, and treatment success rates are as high as 95 percent in cats.

Your veterinarian may ask you to give your cat methimazole twice a day for up to a year.

Methimazole for cats comes in pill and liquid forms, and as a paste that you apply to the inside of your cat's outer ear.

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

• a beta blocker such as acebutolol (Sectral), atenolol (Tenormin), betaxolol (Kerlone), bisoprolol (Zebeta), carvedilol (Coreg), esmolol (Brevibloc), labetalol (Trandate), metoprolol (Lopressor, Toprol XL), nadolol (Corgard), nebivolol (Bystolic), penbutolol (Levatol), propranolol (Inderal), sotalol (Betapace), timolol (Blocadren)
• digoxin (Digitek, Lanoxin)
• theophylline (Theo-24,  Theobid, Theo-Dur, Theolair, Elixophyllin, Elixophylline, Quibron-T, Uniphyl)
• warfarin (Coumadin, Jantoven)

This is not a complete list of Tapazole drug interactions. Ask your doctor or pharmacist for more information.

Medications can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of Tapazole, there are no specific foods that you must exclude from your diet when receiving this medication.

• Take Tapazole exactly as prescribed.
• This medication comes in tablet form and is usually taken 3 times daily.
• Tapazole can be taken with or without food.
• If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose.

Take Tapazole exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

The Tapazole dose your doctor recommends will be based on the following:

• the condition being treated
• other medical conditions you have
• other medications you are taking
• how you respond to this medication
• your weight (children)

The recommended starting daily dosage is 15 mg for mild hyperthyroidism, 30 to 40 mg for moderately severe hyperthyroidism, and 60 mg for severe hyperthyroidism, divided into 3 doses at 8-hour intervals.

The maintenance dosage is 5 to 15 mg daily.

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 purposes not listed in this medication guide.

Antithyroid agent;101 thioimidazole-derivative.b

Storage

Oral

15–30°C.101

• Importance of informing clinicians immediately if signs or symptoms of illness (e.g., sore throat, skin eruptions, fever, chills, headache, general malaise) occur.101 b Importance of immediately discontinuing the drug and contacting clinicians if signs or symptoms suggestive of agranulocytosis (e.g., fever, sore throat) occur.101 118 (See Hematologic Effects under Cautions.)

• Importance of immediately discontinuing the drug and promptly informing clinicians if symptoms suggestive of hepatic injury (e.g., pruritic rash, jaundice, acholic stools, dark urine, arthralgias, abdominal pain, nausea, fatigue) occur.118 (See Hepatotoxicity under Cautions.)

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses.101

• Importance of women immediately informing clinicians if they are or plan to become pregnant or plan to breast-feed.101 Necessity for clinicians to advise women of methimazole-associated fetal malformations, as well as risks of propylthiouracil-associated hepatotoxicity when considering antithyroid drug use during pregnancy.101 104 106 109

• Importance of informing patients of other important precautionary information.101 (See Cautions.)

• It is used to treat an overactive thyroid gland.

• Store at room temperature.
• Store in a dry place. Do not store in a bathroom.
• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Check with your pharmacist about how to throw out unused drugs.

First Trimester Use of Methimazole and Congenital Malformations

Methimazole crosses the placental membranes and can cause fetal harm, when administered in the first trimester of pregnancy. Rare instances of congenital defects, including aplasia cutis, craniofacial malformations (facial dysmorphism; choanal atresia), gastrointestinal malformations (esophageal atresia with or without tracheoesophageal fistula), omphalocele and abnormalities of the omphalomesenteric duct have occurred in infants born to mothers who received Tapazole in the first trimester of pregnancy. If Tapazole is used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the potential hazard to the fetus.

Because of the risk for congenital malformations associated with use of Tapazole in the first trimester of pregnancy, it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism. If Tapazole is used, the lowest possible dose to control the maternal disease should be given.

Agranulocytosis

Agranulocytosis is potentially a life-threatening adverse reaction of Tapazole therapy. Patients should be instructed to immediately report to their physicians any symptoms suggestive of agranulocytosis, such as fever or sore throat. Leukopenia, thrombocytopenia, and aplastic anemia (pancytopenia) may also occur. The drug should be discontinued in the presence of agranulocytosis, aplastic anemia (pancytopenia), ANCA-positive vasculitis, hepatitis, or exfoliative dermatitis and the patient's bone marrow indices should be monitored.

Liver Toxicity

Although there have been reports of hepatotoxicity (including acute liver failure) associated with Tapazole, the risk of hepatotoxicity appears to be less with methimazole than with propylthiouracil, especially in the pediatric population. Symptoms suggestive of hepatic dysfunction (anorexia, pruritis, right upper quadrant pain, etc.) should prompt evaluation of liver function (bilirubin, alkaline phosphatase) and hepatocellur integrity (ALT, AST). Drug treatment should be discontinued promptly in the event of clinically significant evidence of liver abnormality including hepatic transaminase values exceeding 3 times the upper limit of normal.

Hypothyroidism

Tapazole can cause hypothyroidism necessitating routine monitoring of TSH and free T4 levels with adjustments in dosing to maintain a euthyroid state. Because the drug readily crosses placental membranes, methimazole can cause fetal goiter and cretinism when administered to a pregnant woman. For this reason, it is important that a sufficient, but not excessive, dose be given during pregnancy (see PRECAUTIONS, Pregnancy).

Applies to methimazole: oral tablet

Along with its needed effects, methimazole (the active ingredient contained in Tapazole) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking methimazole:

• Backache
• black, tarry stools
• chest pain
• chills
• cough
• fever
• increase or decrease in urination
• painful or difficult urination
• shortness of breath
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swelling of the feet or lower legs
• swollen glands
• unusual bleeding or bruising
• unusual tiredness or weakness

• Abdominal or stomach pain
• bleeding gums
• blood in the urine or stool
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• dark urine
• difficulty with moving
• general feeling of discomfort or weakness
• headache
• joint pain
• light-colored stools
• loss of appetite and weight
• lower back or side pain
• muscle aching or cramping
• muscle pain or stiffness
• nausea and vomiting
• numbness or tingling of the hands, feet, or face
• pinpoint red spots on the skin
• sore muscles
• swollen joints
• swollen salivary glands
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• tightness in the chest
• wheezing
• yellow eyes or skin

Some side effects of methimazole may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

• Abnormal loss of hair
• dizziness or lightheadedness
• feeling of constant movement of self or surroundings
• heartburn
• hives or welts
• itching
• loss of taste
• pain or discomfort in the chest, upper stomach, or throat
• red skin
• skin rash
• sleepiness
• vomiting