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Methimazole Tablets (100 ct) Manufacturer May Vary

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Methimazole Tablets are used for the treatment of hyperthyroidism in cats.

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Description

Methimazole Tablets are used for the treatment of hyperthyroidism in cats. Made by Heritage Pharmaceuticals.

Additional information

Weight N/A
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Strength

5 mg, 10 mg

More Details

This medication requires a prescription from your veterinarian.  This medication is labeled for human use and is a chemically generic equivalent to the veterinary drug, Felimizole (methimazole).  Methimazole generic is available in 5 mg and 10 mg tablets in comparison with Felimizole (2.5 mg and 5 mg tablets).

Methimazole is a thioureylene antithyroid drug, which inhibits the synthesis of thyroid hormones.  Methimazole is considered by most clinicians in North America as the drug of choice when using medications to treat feline hyperthyroidism.

Formulations

Methimazole Tablets are available in 5 mg or 10 mg tablets in a 100 ct bottle.

Administration

Use as directed by your veterinarian.

DOSE RECOMMENDATIONS -The starting dose of METHIMAZOLE Coated Tablets is 2.5 mg orally every 12 hours. Following 3 weeks of treatment, the dose should be titrated to effect as directed by your veterinarian.   The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration.

Precautions

WARNINGS: Methimazole has anti-vitamin K activity and may induce bleeding without evidence of platelet deficiency.

Keep out of reach of children.

For use in cats only.

Wash hands with soap and water after administration to avoid exposure to drug. Do not break or crush tablets. Wear protective gloves to prevent direct contact with litter, feces, urine, or vomit of treated cats, and broken or moistened tablets. Wash hands after contact with the litter of treated cats.

Methimazole is a human teratogen and crosses the placenta concentrating in the fetal thyroid gland. There is also a high rate of transfer into breast milk. Pregnant women or women who may become pregnant, and nursing mothers should wear gloves when handling tablets, litter or bodily fluids of treated cats.

Methimazole may cause vomiting, gastric distress, headache, fever, painful joints, itching, and low white blod cell counts.

In the event of accidental ingestion/overdose, seek medical advice immediately and show the product label to the physician.

PRECAUTIONS: Use of FELIMAZOLE Coated Tablets in cats with renal dysfunction should be carefully evaluated.

The most common adverse reactions include change in food consumption (increase or decrease), lethargy, vomiting, diarrhea/loose stool, skin lesions, and abnormal vocalization.

Drug Interactions

The following drug interactions have either been reported or are theoretical in humans or animals receiving methimazole and may be of significance in veterinary patients. Unless otherwise noted, use together is not necessarily contraindicated, but weigh the potential risks and perform additional monitoring when appropriate.

  • BENZIMIDAZOLE ANTIPARASITICS: Methimazole can reduce hepatic oxidation of benzimidazoles and increase blood levels.
  • BETA-BLOCKERS: Veterinary label states: A reduction in dose may be needed when the patient becomes euthyroid.
  • BUPROPION: Potential for increased risk for hepatotoxicity; increased monitoring (LFTs) necessary.
  • DIGOXIN: Methimazole may decrease digoxin efficacy, but the veterinary label states: A reduction in dose may be needed when the patient becomes euthyroid.
  • PHENOBARBITAL: Veterinary label states: Concurrent use of phenobarbital may reduce the clinical effectiveness.
  • THEOPHYLLINE: Veterinary label states: A reduction in dose may be needed when the patient becomes euthyroid.
  • WARFARIN: In human hyperthyroid patients, the metabolism of vitamin K clotting factors is increased, resulting in increased sensitivity to oral anticoagulants. By reducing the effects of hyperthyroidism, methimazole may decrease clotting factor metabolism reduce the effects of warfarin. However, patients that are euthyroid on methimazole and receiving warfarin may develop hypoprothrombinemia if methimazole is stopped and they once again become thyrotoxic. The veterinary label states: Anticoagulants may be potentiated by methimazole. Recommendation: If methimazole and warfarin are used together, increased monitoring anticoagulant effect is warranted.

 

Manufacturer Product Information

METHIMAZOLE- methimazole tablet 
Heritage Pharmaceuticals Inc.

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Rx only


DESCRIPTION

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.

Each tablet 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 114.17, and the molecular formula is C4H6N2S. The structural formula is as follows:


CLINICAL 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.


INDICATIONS AND USAGE

Methimazole is 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.


CONTRAINDICATIONS

Methimazole is contraindicated in the presence of hypersensitivity to the drug or any of the other product components.


WARNINGS

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 in the first trimester of pregnancy. If methimazole 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 methimazole in the first trimester of pregnancy it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism. If methimazole is 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, 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 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 PRECAUTIONS, Pregnancy).


PRECAUTIONS


General

Patients who receive methimazole should be under close surveillance and should be cautioned to report immediately any evidence of illness, particularly sore throat, skin eruptions, fever, headache, or general malaise. In such cases, white-blood-cell and differential counts should be obtained to determine whether agranulocytosis has developed. Particular care should be exercised with patients who are receiving additional drugs known to cause agranulocytosis.


Information for Patients

Patients should be advised that if they become pregnant or intend to become pregnant while taking an antithyroid drug, they should contact their physician immediately about their therapy.


Laboratory Tests

Because methimazole may cause hypoprothrombinemia and bleeding, prothrombin time should be monitored during therapy with the drug, especially before surgical procedures. Thyroid function tests should be monitored periodically during therapy. Once clinical evidence of hyperthyroidism has resolved, the finding of a rising serum TSH indicates that a lower maintenance dose of methimazole should be employed.


Drug Interactions

Anticoagulants (oral):

Due to potential inhibition of vitamin K activity by methimazole, the activity of oral anticoagulants (e.g., warfarin) may be increased; additional monitoring of PT/INR should be considered, especially before surgical procedures.

β-adrenergic blocking agents:

Hyperthyroidism may cause an increased clearance of beta blockers with a high extraction ratio. A dose reduction of beta-adrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid.

Digitalis glycosides:

Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid; a reduced dosage of digitalis glycosides may be needed.

Theophylline:

Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed.


Carcinogenesis, Mutagenesis, Impairment of Fertility

In a 2 year study, rats were given methimazole at doses of 0.5, 3, and 18 mg/kg/day. These doses were 0.3, 2, and 12 times the 15 mg/day maximum human maintenance dose (when calculated on the basis of surface area). Thyroid hyperplasia, adenoma, and carcinoma developed in rats at the two higher doses. The clinical significance of these findings is unclear.


Pregnancy

Pregnancy Category D

(See WARNINGS)

If methimazole is used during the first trimester of pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the potential hazard to the fetus.

In pregnant women with untreated or inadequately treated Graves' disease, there is an increased risk of adverse events of maternal heart failure, spontaneous abortion, preterm birth, stillbirth and fetal or neonatal hyperthyroidism.

Because methimazole crosses placental membranes and can induce goiter and cretinism in the developing fetus, hyperthyroidism should be closely monitored in pregnant women and treatment adjusted such that a sufficient, but not excessive, dose be given during pregnancy. In many pregnant women, the thyroid dysfunction diminishes as the pregnancy proceeds; consequently, a reduction of dosage may be possible. In some instances, anti-thyroid therapy can be discontinued several weeks or months before delivery.

Due to the rare occurrence of congenital malformations associated with methimazole use, it may be appropriate to use an alternative anti-thyroid medication in pregnant women requiring treatment for hyperthyroidism particularly in the first trimester of pregnancy during organogenesis.

Given the potential maternal adverse effects of propylthiouracil (e.g., hepatotoxicity), it may be preferable to switch from propylthiouracil to methimazole for the second and third trimesters.


Nursing Mothers

Methimazole is present in breast milk. However, several studies found no effect on clinical status in nursing infants of mothers taking methimazole. A long-term study of 139 thyrotoxic lactating mothers and their infants failed to demonstrate toxicity in infants who are nursed by mothers receiving treatment with methimazole. Monitor thyroid function at frequent (weekly or biweekly) intervals.


Pediatric Use

Because of postmarketing reports of severe liver injury in pediatric patients treated with propylthiouracil, methimazole is the preferred choice when an antithyroid drug is required for a pediatric patient (see DOSAGE AND ADMINISTRATION).


ADVERSE REACTIONS

Major adverse reactions (which occur with much less frequency than the minor adverse reactions) include inhibition of myelopoieses (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.

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.


OVERDOSAGE

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.


DOSAGE AND ADMINISTRATION

Methimazole is 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.


HOW 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:

Bottles of 100             NDC 23155-070-01

Bottles of 1000           NDC 23155-070-10

Methimazole Tablets USP, 10 mg - round, white to off white bi-convex tablet. Debossed HP bisect 71 on one side and plain on the reverse side.

They are available in:

Bottles of 100            NDC 23155-071-01

Bottles of 1000          NDC 23155-071-10

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.

Manufactured for:

Heritage Pharmaceuticals Inc.

Eatontown, NJ 07724

1.866.901.DRUG (3784)

51U000000174US02

Revised: 12/2015

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