Source: European Medicines Agency (EU) Revision Year: 2019
Treatment of hyperthyroidism, including:
Thiamazole is the active metabolite of carbimazole, but 1mg of thiamazole is not equivalent to 1 mg of carbimazole.This should be kept in mind when starting therapy with thiamazole or in case of switch from carbimazole to thiamazole. The following doses recommendations should be followed.
Depending on the severity of the disease and the iodine supply, treatment is usually initiated with daily thiamazole doses between 10 to 40 mg. In many cases, inhibition of thyroid hormone production can usually be achieved with initial doses of 20 to 30 mg thiamazole daily. In milder cases, a full blocking dose may not be required, thus, a lower initial dose may be considered. In severe cases of hyperthyroidism an initial dose of 40 mg thiamazole may be required.
The dose is individually adjusted depending on the metabolic condition of the patient, as indicated by the development of thyroid hormone status.
For maintenance therapy, one of the following treatment options is recommended:
a) Daily maintenance dose of 5 to 20 mg thiamazole in combination with levothyroxine, in order to avoid hypothyroidism.
b) Monotherapy with daily doses of 2.5 to 10 mg thiamazole. Iodine-induced hyperthyroidism may require higher doses.
The average initial dosage in children is 0.5 mg thiamazole/kg body weight per day. After normalisation of the thyroid function, the dose is stepwise reduced to a lower maintenance dose, which depends on the metabolic condition of the patient. Additional treatment with levothyroxine may be required to avoid hypothyroidism.
The aim of therapy is to achieve a euthyroid metabolic condition and long-term remission after a limited duration of treatment. Depending on the selection of the treated patients, one-year remission can be achieved in 50% of cases at the most. The reported remission rates vary considerably without underlying reasons having been completely clarified. The type of hyperthyroidism (immunogenic or non-immunogenic), the duration of treatment, the thiamazole dose as well as dietary or iatrogenic iodine supply, are probably influencing factors.
In conservative treatment of hyperthyroidism therapy is usually continued over a period of 6 months to 2 years (1 year on average). Statistically, the probability of remission increases with the duration of therapy. In cases where remission of the disease cannot be achieved and definite therapeutic measures do not apply or are rejected, thiamazole may be used as long-term anti-thyroid therapy in as low a dosage as possible without addition or together with a small quantity of levothyroxine.
Patients with large goitres and constriction of the trachea should, if at all, only undergo short-term treatment with thiamazole since long-term administration can result in goitre growth. It may be necessary to monitor therapy particularly thoroughly (TSH level, tracheal lumen). The treatment is preferably combined with additional administration of levothyroxine.
Temporary pre-treatment (for 3 to 4 weeks or longer, in individual cases) may serve to achieve a euthyroid metabolic condition, thus reducing operative risks.
Surgery should be performed as soon as the patient is euthyroid. Otherwise, supplementary levothyroxine must be administered. Treatment may be terminated the day before surgery.
The thiamazole induced increased brittleness and bleeding risk of the thyroid tissue may be compensated by additional pre-operative administration of high dosed iodine in the last ten days before surgery (Plummer’s iodine therapy).
Achievement of a euthyroid metabolism before initiation of radioiodine therapy is important particularly in severe cases of hyperthyroidism, as post-therapeutic thyrotoxic crisis has occurred in individual cases after such therapy without pre-treatment.
Note: Thionamide derivatives may reduce the radio-sensitivity of the thyroid tissue. In scheduled radioiodine therapy of autonomous adenomas activation of paranodular tissue by means of pretreatment must be prevented.
The duration and dose of treatment must be adjusted individually depending on the severity of the clinical picture and the estimated period until radioiodine therapy starts to be effective (approx. 4 to 6 months).
In general, daily doses of 10 to 20 mg thiamazole and/or 1 g perchlorate are administered for approx. 10 days (e.g. for renally excreted contrast media). The duration of treatment depends on the period of time for which the iodine-containing substance is retained in the body.
In patients with hepatic impairment, the plasma clearance of thiamazole is reduced. Therefore, the dose should be kept as low as possible and patients should be closely monitored.
As there is a lack of data regarding pharmacokinetic behaviour of Thiamazol in patients with renal impairment, careful individual dose adjustment under close monitoring is recommended. The dose should be kept as low as possible.
Although no dose accumulation is expected in elderly patients, careful individual dose adjustment under close monitoring is recommended.
The tablets are swallowed whole with sufficient liquid.
During high-dose initial therapy of hyperthyroidism the above stated daily doses can be subdivided and taken at regular intervals over the day.
The maintenance dose can be taken at once in the morning during or after breakfast.
Overdose leads to hypothyroidism with corresponding symptoms of a reduced metabolism and, through the feedback effect, to activation of the adenohypophysis with subsequent goitre growth. This can be avoided by dose reduction as soon as a euthyroid metabolic condition is achieved and, if necessary, by additional administration of levothyroxine (see section 4.2).
Negative consequences of accidental ingestion of high doses of thiamazole are not known.
4 years.
Do not store above 25°C.
Blister consisting of a polyvinyl chloride film and an aluminium cover foil.
Pack sizes:
Thyrozol 5 mg: 20, 30, 50, 100 film-coated tablets.
Thyrozol 10 mg: 20, 30, 50, 100 film-coated tablets.
Thyrozol 20 mg: 20, 30, 50 film-coated tablets.
Not all pack sizes may be marketed.
No special requirements.
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