Thyrozol Special Precautions

Thyrozol should not be used in patients with history of mild hypersensitivity reactions (e.g. allergic rashes, pruritus).
Thyrozol should only be used in short-term treatment and with careful medical monitoring in patients with large goitres with constriction of the trachea because of the risk of goitre growth.
Myelotoxicity: Agranulocytosis has been reported to occur in about 0.3 to 0.6% of cases. Therefore, patients must be informed prior to the start of therapy of the related symptoms (stomatitis, pharyngitis, fever). It usually occurs during the first few weeks of treatment, but may still manifest some months after the start of therapy and upon its reintroduction. A close monitoring of blood count is recommended before and after initiation of therapy especially in cases with pre-existing mild granulocytopenia.
In the case that any of these symptoms occur, especially during the first few weeks of treatment, patients should be advised to contact their physician immediately for a blood count. If agranulocytosis is confirmed, the medicinal product must be discontinued.
Other myelotoxic adverse reactions rarely occur in the recommended dose range. They have frequently been reported in connection with very high doses of thiamazole (about 120 mg per day). These dosages should be reserved for special indications (severe courses of disease, thyrotoxic crisis). Occurrence of damage to the bone marrow during treatment with thiamazole requires discontinuation of the medication and, if necessary, switching to an anti-thyroid drug of another substance group.
Pancreatitis: There have been post-marketing reports of acute pancreatitis in patients receiving thiamazole or its prodrug carbimazole. In case of acute pancreatitis, thiamazole should be discontinued immediately. Thiamazole must not be given to patients with a history of acute pancreatitis after administration of thiamazole or its prodrug carbimazole. Re-exposure may result in recurrence of acute pancreatitis, with decreased time to onset.
Vasculitis: Cases of vasculitis have been observed very rarely in patients receiving thiamazole therapy. The cases of vasculitis include: leukocytoclastic cutaneous vasculitis, glomerulonephritis, and systemic vasculitis (with fatal outcome). Many cases were associated with anti-neutrophilic cytoplasmic antibodies (ANCA)-positive vasculitis. Early recognition of vasculitis is important to prevent long term organ damage and/or death. Inform patients to promptly report symptoms that may be associated with vasculitis including rash, hematuria or decreased urine output, dyspnea or hemoptysis. If vasculitis is suspected, discontinue thiamazole therapy and initiate appropriate intervention.
Women of childbearing potential and pregnancy: Women of childbearing potential have to use effective contraceptive measures during treatment. The use of thiamazole in pregnant women must be based on the individual benefit/risk assessment. If thiamazole is used during pregnancy, the lowest effective dose without additional administration of thyroid hormones should be administered. Close maternal, foetal, and neonatal monitoring is warranted.
Control of hypothyroidism: Excess dosage can lead to subclinical or clinical hypothyroidism and goiter growth due to TSH increase. Therefore, the dose of thiamazole should be reduced as soon as a euthyroid metabolic condition is achieved and if necessary, levothyroxine should be given additionally. It is not useful, to discontinue thiamazole altogether and to continue with levothyroxine only.
Goitre growth under therapy with thiamazole in spite of suppressed TSH is a result of the underlying disease and cannot be prevented by additional treatment with levothyroxine.
Achievement of normal TSH levels is crucial to minimize the risk of occurrence or deterioration of endocrine orbitopathy. However, this condition is frequently independent of the course taken by the thyroid disease. Such a complication itself does not constitute a reason to change the adequate treatment regimen and is not to be regarded as an adverse reaction of appropriately performed therapy.
At a low percentage, late hypothyroidism can occur after anti-thyroid therapy without any additional ablative measures. This is probably not an adverse drug reaction, but to be regarded as inflammatory and destructive processes in the thyroid parenchyma due to the underlying disease.
The reduction in the pathologically increased energy consumption in hyperthyroidism can lead to a (generally desired) gain in body weight during treatment with thiamazole. The patients are to be informed that their energy consumption normalizes along with the improving clinical picture.
Thyrozol contains lactose; therefore, patients with hereditary galactose intolerance, lactase deficiency or glucose-galactose malabsorption should not take this medicinal product.
Effects on ability to drive and use machines: Thiamazole does not affect the ability to drive a vehicle or to operate machinery.