Brand Name
Methimazole
View Brand InformationFDA approval date: March 27, 2001
Classification: Thyroid Hormone Synthesis Inhibitor
Form: Tablet
What is Methimazole?
Methimazole tablets are indicated: In patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter for whom surgery or radioactive iodine therapy is not an appropriate treatment option., To ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy.
Approved To Treat
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Brand Information
Methimazole (Methimazole)
1DESCRIPTION
Methimazole (1-methylimidazole-2-thiol) is a white, crystalline substance that is freely soluble in water. It differs chemically from the drugs of the thiouracil series primarily because it has a 5- instead of a 6-membered ring.
Methimazole tablet, USP contains 5 or 10 mg (43.8 or 87.6 μmol) methimazole, an orally administered antithyroid drug.
Each tablet also contains lactose monohydrate, magnesium stearate, pregelatinized starch and talc.
The molecular weight is 114.16, and the molecular formula is C
2CLINICAL PHARMACOLOGY
Methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism. The drug does not inactivate existing thyroxine and tri-iodothyronine that are stored in the thyroid or circulating in the blood nor does it interfere with the effectiveness of thyroid hormones given by mouth or by injection.
Methimazole is readily absorbed in the gastrointestinal tract, metabolized in the liver, and excreted in the urine.
3INDICATIONS AND USAGE
Methimazole tablets are indicated:
- In patients with Graves' disease with hyperthyroidism or toxic multinodular goiter for whom surgery or radioactive iodine therapy is not an appropriate treatment option.
- To ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy.
4CONTRAINDICATIONS
Methimazole tablets are contraindicated in the presence of hypersensitivity to the drug or any of the other product components.
5WARNINGS
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 methimazole tablets in the first trimester of pregnancy. If methimazole tablets are 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 methimazole tablets in the first trimester of pregnancy it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism. If methimazole tablets are used, the lowest possible dose to control the maternal disease should be given.
Agranulocytosis
Agranulocytosis is potentially a life-threatening adverse reaction of methimazole 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 or aplastic anemia (pancytopenia), 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 methimazole, 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 hepatocellular 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
Methimazole 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
Vasculitis
Cases of vasculitis resulting in severe complications have been reported in patients receiving methimazole therapy. These cases of vasculitis include: leukocytoclastic cutaneous vasculitis, acute kidney injury and glomerulonephritis, alveolar/pulmonary hemorrhage, CNS vasculitis, and neuropathy. Most cases were associated with anti-neutrophilic cytoplasmic antibodies (ANCA)-positive vasculitis. In some cases, vasculitis resolved/improved with drug discontinuation; however, more severe cases required treatment with additional measures including corticosteroids, immunosuppressant therapy, and plasmapheresis. If vasculitis is suspected, discontinue therapy and initiate appropriate intervention.
6ADVERSE REACTIONS
Major adverse reactions (which occur with much less frequency than the minor adverse reactions) include inhibition of myelopoiesis (agranulocytosis, granulocytopenia, thrombocytopenia, and aplastic anemia), drug fever, a lupus-like syndrome, insulin autoimmune syndrome (which can result in hypoglycemic coma), hepatitis (jaundice may persist for several weeks after discontinuation of the drug), periarteritis, and hypoprothrombinemia. Nephritis occurs very rarely. There have been postmarketing case reports of acute pancreatitis.
There are reports of a vasculitis, often associated with the presence of anti-neutrophilic cytoplasmic antibodies (ANCA), resulting in severe complications (see
Minor adverse reactions include skin rash, urticaria, nausea, vomiting, epigastric distress, arthralgia, paresthesia, loss of taste, abnormal loss of hair, myalgia, headache, pruritus, drowsiness, neuritis, edema, vertigo, skin pigmentation, jaundice, sialadenopathy, and lymphadenopathy.
7OVERDOSAGE
Signs and Symptoms
Symptoms may include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema. Aplastic anemia (pancytopenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression. No information is available on the median lethal dose of the drug or the concentration of methimazole in biologic fluids associated with toxicity and/or death.
Treatment
To obtain up-to-date information about the treatment of overdose, a good resource is your certified Regional Poison Control Center. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in the patient.
In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient's medical status.
8DOSAGE AND ADMINISTRATION
Methimazole tablets are administered orally. The total daily dosage is usually given in 3 divided doses at approximately 8-hour intervals.
Adult - The initial 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.
Pediatric - Initially, the daily dosage is 0.4 mg/kg of body weight divided into 3 doses and given at 8-hour intervals. The maintenance dosage is approximately 1/2 of the initial dose.
9HOW SUPPLIED
Methimazole tablets, USP 5 mg - round, white to off white bi-convex tablet. Debossed HP bisect 70 on one side and plain on the reverse side.
They are available in:
NDC: 70518-1506-00
NDC: 70518-1506-01
NDC: 70518-1506-02
PACKAGING: 30 in 1 BLISTER PACK
PACKAGING: 100 in 1 BOX
PACKAGING: 1 in 1 POUCH
Store at 20° to 25°C (68° to 77°F); excursions permitted between 15° to 30°C (59° to 86°F) [See USP Controlled Room Temperature].
Dispense in tight, light-resistant container.
Repackaged and Distributed By:
Remedy Repack, Inc.
625 Kolter Dr. Suite #4 Indiana, PA 1-724-465-8762
10PRINCIPAL DISPLAY PANEL
DRUG: Methimazole
GENERIC: Methimazole
DOSAGE: TABLET
ADMINSTRATION: ORAL
NDC: 70518-1506-0
NDC: 70518-1506-1
NDC: 70518-1506-2
COLOR: white
SHAPE: ROUND
SCORE: Two even pieces
SIZE: 6 mm
IMPRINT: HP;70
PACKAGING: 30 in 1 BLISTER PACK
PACKAGING: 100 in 1 BOX
PACKAGING: 1 in 1 POUCH
ACTIVE INGREDIENT(S):
- METHIMAZOLE 5mg in 1
INACTIVE INGREDIENT(S):
- LACTOSE MONOHYDRATE
- MAGNESIUM STEARATE
- STARCH, CORN
- TALC
