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General: Patients who receive thiamazole 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 made to determine whether agranulocytosis has developed. Particular care should be exercised with patients who are receiving additional drugs known to cause agranulocytosis.
Laboratory Tests: Because thiamazole may cause hypoprothrombinemia and bleeding, prothrombin time should be monitored during therapy with the drug, especially before surgical procedures (see General Precautions).
Periodic monitoring of thyroid function is warranted and the finding of an elevated TSH warrants a decrease in the dosage of thiamazole.
Carcinogenicity, Mutagenicity & Impairment of Fertility: In a 2-year study, rats were given thiamazole 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 2 higher doses. The clinical significance of these findings is unclear.
Use in pregnancy & lactation: (See Warnings). Thiamazole used judiciously is an effective drug in hyperthyroidism complicated by pregnancy. In many pregnant women, the thyroid dysfunction diminishes as the pregnancy proceeds; consequently, a reduction in dosage may be possible. In some instances, use of thiamazole can be discontinued 2-3 weeks before delivery.
Thiamazole appears in human breast milk and its use is contraindicated in nursing mothers (see Warnings).
Use in children: See Dosage & Administration.
