Methimazole: Uses, Side Effects, Dosage And More
Methimazole
How Does Methimazole Work?
Methimazole has a specific way of working in the thyroid gland. The drug binds permanently to TPO's active site & prevents the iodination of tyrosine residues on thyroglobulin. This action prevents the synthesis of thyroxine (T4) and triiodothyronine (T3) that reduces thyroid hormone levels in the body.
The effects start within 12-18 hours after taking the medicine and last 36-72 hours.
Uses of Methimazole
Doctors use methimazole to treat several conditions:
Treatment of Graves' disease with hyperthyroidism
Management of toxic multinodular goitre
Preparation before thyroid surgery or radioactive iodine therapy
Long-term treatment option for patients who can't have surgery or radiation
How & When to Take Methimazole?
You can take methimazole with or without food, but stick to one approach.
The usual schedule splits doses equally about every 8 hours. Take it at the same time each day to get the best results.
Talk to your doctor before stopping the medication as this could make your condition worse.
What Are the Side Effects of Methimazole?
Common side effects:
Stomach upset
Nausea or vomiting
Mild skin rash or itching
Abnormal hair loss
Joint and muscle pain
Changes in taste sensation
You need immediate medical help if you experience fever, sore throat, unusual bleeding, pain in your right abdomen, or if your skin or eyes turn yellow.
Can I Take Methimazole Daily?
Yes, daily doses of methimazole help maintain steady blood levels. Adults usually take 5-15 mg per day as a maintenance dose. Studies show that methimazole is safe to use long-term for patients with Graves' disease.
Precautions
You must tell your doctor about any existing medical conditions especially when you have liver disease, low white blood cell counts, or allergies to medications.
Pregnant women need extra caution because methimazole can harm unborn babies, especially during the first trimester. Nursing mothers should talk to their doctor before starting treatment.
Blood tests help monitor for agranulocytosis, a rare but serious side effect.
Your doctor should check liver function if symptoms like jaundice, anorexia, or pruritus appear.
Keep methimazole at room temperature between 68°F and 77°F (20°C to 25°C) in a cool, dry place away from light.
What If I Missed a Dose?
Take the missed dose as soon as you remember. But if it's almost time for your next scheduled dose, skip the missed one and stick to your regular schedule. Never take a double dose to make up for a forgotten one. A consistent amount in your bloodstream will give a better result.
What If I Overdose?
Overdose symptoms include:
Nausea
Vomiting
Headache
Joint pain
Fever
Swelling
Unusual bleeding
Seizures
Confusion
Irregular heartbeat
Collapse
Get emergency care immediately. Keep the medication container ready along with your age, weight, and time of ingestion information.
Drug Interactions
Key drug interactions are:
Blood thinners like warfarin
Beta-blockers
Digoxin
Immunosuppressants like azathioprine
Methotrexate
Theophylline
Dosage for Methimazole
Adult dosing varies by severity:
Mild hyperthyroidism: 15 mg/day as the original dose
Moderate cases: 30-40 mg/day
Severe cases: 60 mg/day
Maintenance: 5-15 mg/day
Children's dosage depends on their weight - 0.4-0.7 mg/kg/day as the original dose
Daily doses are usually split into three equal portions taken every 8 hours. Doctors gradually reduce to maintenance levels after 4-8 weeks.
Methimazole vs Propylthiouracil (PTU)
MMI and PTU are the main treatments doctors use for hyperthyroidism, with some clear differences between them:
Feature | Methimazole | Propylthiouracil |
Efficacy | More effective at normalising FT4 levels | Less effective in severe cases |
Duration of Action | Longer (36-72 hours) | Shorter (12-24 hours) |
Daily Dosage | Lower (15-30 mg) | Higher (150-300 mg) |
Dosing Frequency | Once daily possible | Multiple daily doses needed |
Liver Function Impact | Lower risk of liver damage | Higher risk of hepatotoxicity |
Pregnancy Safety | Higher risk of birth defects | Preferred in first trimester |
Birth Defect Types | More severe (aplasia cutis, esophageal atresia) | Less severe, surgically correctable |
Patients taking a single 15 mg daily dose of MMI show better results than those taking 150 mg PTU when treating Graves' hyperthyroidism. Research also shows that MMI reduces T3, T4, FT3, and FT4 levels better.
FAQs
What is methimazole used for?
Doctors use methimazole to treat hyperthyroidism, a condition where the thyroid gland makes too many hormones. The medication works best when you have Graves' disease and a toxic multinodular goitre. Doctors prescribe it to prepare the body before thyroid surgery or radioactive iodine therapy.
How does methimazole work in the body?
The medication stops the enzyme thyroid peroxidase that helps create thyroid hormones. This blocking action prevents the body from making thyroxine (T4) and triiodothyronine (T3). Patients start seeing effects in 12-18 hours, but noticeable improvements take several weeks.
What is the usual dosage of methimazole for adults and children?
Adult doses start from 15mg daily for mild cases and can go up to 60mg daily for severe hyperthyroidism. Patients take these doses split into three parts every 8 hours. Children need 0.4mg/kg at first, then the dose drops to about half for maintenance.
Can methimazole be used to treat hyperthyroidism?
Yes! Methimazole remains the top choice for treating hyperthyroidism. The medication helps manage Graves' disease and thyrotoxicosis in cases where surgery or radioactive treatments don't fit the patient's needs.
What are the common side effects of methimazole?
Common reactions include:
Skin rashes and itching occur most often
Nausea and stomach upset
Hair loss and altered taste
Joint and muscle pain
Dizziness and drowsiness
Serious side effects:
Agranulocytosis
Liver problems
Severe allergic reactions
Is methimazole safe for long-term use?
Methimazole is safe over extended periods. Studies found that a few had adverse reactions
after 48 months of use.
Can methimazole interact with other medications?
Methimazole can interact with many drugs. Doctors need to know about all your current medications. Key interactions include:
Blood thinners like warfarin
Beta-blockers such as metoprolol, atenolol, and propranolol
Digoxin
Theophylline
Is methimazole safe during pregnancy or breastfeeding?
The placenta allows methimazole to pass through, which can harm developing babies, especially during the first trimester.
Mothers can safely take doses up to 20mg daily without affecting their child's thyroid function or intellectual development. You can reduce your baby's exposure by taking methimazole right after breastfeeding and waiting 3-4 hours before the next feeding.
What precautions should be taken while using methimazole?
Medical check-ups are vital while taking this medicine. Your doctor will use blood & urine tests to detect potential side effects early. Extra caution is needed if you have liver disease, low white blood cell counts, or allergies to certain medications. Let your doctors know about your Methimazole usage before any surgery, including dental procedures.
What should I do if I miss a dose of methimazole?
Take your forgotten dose as soon as you remember. However, skip the missed dose if it's almost time for your next one and continue with your regular medicine. Never take a double dose to make up for a missed one. Consistent timing helps.
