Methima Special Precautions

Hematologic effects: Antithyroid agents have been associated (rarely) with significant bone marrow depression. The most severe manifestation is agranulocytosis. Agranulocytosis is a potentially life-threatening adverse effect of methimazole therapy. Baseline complete blood count, include white count differential, be performed prior to initiating antithyroid drug therapy in patients. Patients receiving methimazole should be closely monitored and should be instructed to contact their clinician immediately if signs or symptoms of illness, particularly sore throat, skin eruptions, fever, chills, headache, or general malaise occur. Aplastic anemia, thrombocytopenia, and leukopenia may also occur. Use with extreme caution in patients receiving other drugs known to cause myelosuppression (particularly agranulocytosis) and in patients >40 years of age; avoid doses ≥40 mg/day.
Hemorrhagic effects: Because antithyroid agents may cause hypoprothrombinemia and bleeding. Monitor prothrombin time during therapy, especially before surgical procedures.
Hepatic effects: Liver function test, including alkaline phosphatase, aminotransferase, and bilirubin, be performed prior to initiating antithyroid drug therapy. Advised to immediately discontinue the drug and promptly contact their clinician if pruritic rash, jaundice, alcoholic stools, dark urine, arthralgias, abdominal pain, or fatigue occurs. Discontinue in the presence of hepatitis (transaminase >3 times upper limit of normal).
Thyroid function: Methimazole can cause hypothyroidism. When methimazole is discontinued, thyroid function should be monitored every 1-3 months for 6-12 months to diagnose relapse early, and patients should be advised to contact clinicians if symptoms of hyperthyroidism occur.