Thyrozol
 

Special warnings and special precautions for use

In hepatic insufficiency plasma clearance of thiamazole is reduced. The selected dose should be as low as possible here.


Interaction with other medicaments and other forms of interaction

Iodine deficiency increases the response to thiamazole, iodine excess lowers the response. There is no information available on the influence of other drugs on the pharmacokinetics and pharmacodynamics of thiamazole.


Pregnancy and lactation

Thyrozol should be given in as low dose as possible in pregnancy without the addition of levothyroxine since only thiamazole but not levothyroxine crosses the placental barrier. There have been no indications of teratogenic effects due to thiamazole. If the dose of thiamazole is too high it may occasionally cause formation of goitre and hypothyroidism in the fetus.
Thiamazole enters breast milk and should therefore be lowdosed in the lactation period (up to 10 mg thiamazole/day).


Effects on ability to drive to to use machines

There are no indications that thiamazole interferes with driving a vehicle, operating machinery, or working without a firm hold.


Undesirable effects

Allergic skin symptoms (pruritus, exanthem, urticaria) are occasionally observed.
Drug fever, hypogeusia and agranulocytosis are rarely seen. These may become manifest even weeks to months after commencement of therapy and may make discontinuation of treatment necessary. The following have also been reported in isolated cases: arthritis, cholestatic jaundice or toxic hepatitis, generalized lymphadenopathy, acute swelling of the salivary glands, thrombopenia, pancytopenia, neuritis and polyneuropathies as well as drug-induced lupus erythematosus.
Before commencement of treatment patients should be advised of the symptoms of agranulocytosis (stomatitis, pharyngitis, fever). In the event of their occurrence the treatment must be stopped immediately and blood count must be made.
Overdosage may precipitate subclinical or clinical hypothyroidism and goitre growth due to TSH increase. Consequently the thiamazole dose should be reduced after the patient becomes euthyroid. Levothyroxine can then be given additionally. Goitre growth during thiamazole therapy where TSH is suppressed is a consequence of the basic disease and cannot be prevented by additional treatment with levothyroxine.
The occurrence of or a deterioration in an endocrine ophthalmopathy is largely independent of the course taken by the thyroid disease and is not to be regarded as a side effect of thiamazole therapy correctly carried out.
In rare cases late hypothyroidism can occur after antithyroid therapy. It is to be regarded as a consequence of inflammatory and destructive processes in the parenchyma of the thyroid occurring alongside the basic disease.


Overdose

Overdosage causes goitre growth and hypothyroidism. It necessitates an immediate reduction of the thiamazole dose and additional substitution with levothyroxine.