Metizol (Thiamazole)

Metizol is an antithyroid medication used to manage conditions caused by excess thyroid hormone production.

• Hyperthyroidism: controls overproduction of thyroid hormones and alleviates symptoms.
• Graves disease: helps achieve remission of autoimmune hyperthyroidism.
• Toxic multinodular goiter: reduces hormone output from autonomous nodules.
• Thyroid storm prophylaxis: prevents acute life‑threatening hyperthyroid crisis.

• Thiamazole inhibits thyroid peroxidase, blocking the iodination of tyrosine residues in thyroglobulin and the coupling reactions required for thyroid hormone synthesis. By interfering with these enzymatic steps, it decreases the production of thyroxine (T4) and triiodothyronine (T3), leading to lower circulating thyroid hormone levels.

Adverse reactions may range from mild to severe and should be monitored during therapy.

Common Side Effects

• Nausea: mild gastrointestinal upset.
• Skin rash: erythematous or pruritic lesions.
• Taste disturbances: altered or metallic taste.
• Arthralgia: joint pain without swelling.
• Headache: mild to moderate intensity.
• Mild leukopenia: slight reduction in white blood cells.

Serious or Rare Side Effects

• Agranulocytosis: severe drop in neutrophils, risk of infection.
• Hepatotoxicity: elevated liver enzymes or liver injury.
• Vasculitis: inflammation of blood vessels.
• Severe neutropenia: marked decrease in neutrophil count.
• Stevens‑Johnson syndrome: severe skin and mucous membrane reaction.
• Aplastic anemia: bone‑marrow failure leading to pancytopenia.

Before initiating therapy, clinicians should assess baseline labs and consider patient‑specific risk factors.

• Monitor blood counts: perform regular CBC to detect agranulocytosis early.
• Assess liver function: periodic LFTs are recommended.
• Avoid in pregnancy: category D, potential fetal harm.
• Caution in elderly: increased sensitivity and higher risk of adverse events.
• Adjust based on thyroid function: frequent TSH monitoring to guide dose changes.
• Store at room temperature: keep in the original pack, protect from moisture.

Thiamazole can alter the activity of several concomitant medicines; interactions vary in clinical significance.

Major Interactions (Avoid)

• Lithium: combined use may exacerbate hypothyroidism.
• Warfarin: thiamazole can potentiate anticoagulant effect, increasing bleeding risk.
• Amiodarone: additive effects on thyroid hormone levels.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: reduced efficacy, consider alternative contraception.
• Theophylline: increased metabolism may lower thiamazole levels.
• Rifampin: induces hepatic enzymes, potentially decreasing thiamazole effectiveness.