Prescribing Notes
- Carbimazole tablets 10mg and 15mg are of a very high cost (£81.32 for 10mg and £238.15 for 15mg pack size per 100 tablets – October 23 Drug Tariff). Doses should be prescribed in multiples of 5mg or 20mg tablets where possible.
- Refer to NICE NG145 Thyroid disease: assessment and management.
- Carbimazole should be initiated under specialist advice to ensure the correct diagnosis is made and that treatment is appropriate.
- Carbimazole can be given by titration method or in a block and replacement regimen.
- Carbimazole is a finite treatment and guidance should be given to patients on the proposed treatment duration.
- Carbimazole has rarely been associated with bone marrow suppression and treatment should be stopped promptly if there is clinical or laboratory evidence of neutropenia. Patients should be asked to report symptoms and signs suggestive of infection, especially sore throat. A white blood cell count should be performed if there is any clinical evidence of infection.
- Propylthiouracil may be an alternative for patients who suffer sensitivity reactions to carbimazole and similar advice regarding neutropenia should be given when using this drug. Prescribe 50mg tablets where appropriate (propylthiouracil 25mg and 100mg tablets are of very high cost).
- Severe hepatic reactions have been reported with propylthiouracil, including fatal cases and cases requiring liver transplant. Liver function should be monitored and propylthiouracil discontinued if significant liver-enzyme abnormalities develop.
- Patients with hyperthyroidism planning a pregnancy should be referred to a specialist endocrine team. Propylthiouracil is the drug of choice during early pregnancy and breastfeeding. Patients maintained on carbimazole should be switched to propylthiouracil under specialist guidance.
Cautions
- Carbimazole is associated with an increased risk of congenital malformations, especially when administered in the first trimester of pregnancy and at high doses. Women of childbearing potential should use effective contraception during treatment with carbimazole. See MHRA for further details.
- Cases of acute pancreatitis have been reported very infrequently during treatment with carbimazole. If acute pancreatitis occurs during treatment with carbimazole immediately and permanently stop treatment. Re-exposure to carbimazole may result in life-threatening acute pancreatitis with a decreased time to onset. See MHRA for further details.