- Free T3
- Free T4
- Full blood count including white cell count (WCC)
- Thyroid stimulating hormone
- Liver function tests
- White blood cell differential
Continued until stable
- Every 6 weeks
- Free T3 continued until TSH in reference range
- Free T4 continued until TSH in reference range
- Thyroid stimulating hormone continued until TSH in reference range
- Full blood count if clinical suspicion of agranulocytosis or liver dysfunction
- Liver function tests if clinical suspicion of agranulocytosis or liver dysfunction
Ongoing once stable
- Every 3 months
- Thyroid stimulating hormone
- Free T3 if TSH abnormal
- Free T4 if TSH abnormal
- Creatine phosphokinase if patient experiencing myalgia
- Full blood count in patients who may be confused or have poor memory
If patient develops any signs and symptoms of hepatic disorder, temporarily stop carbimazole and perform LFTs immediately. Where liver function confirmed as abnormal, stop carbimazole.
White blood cells
If the patient develops any signs or symptoms of agranulocytosis or neutropenia, perform WBC count immediately, particularly where there is clinical evidence of infection.
Carbimazole should be stopped promptly upon clinical or laboratory evidence of neutropenia. Consider specialist referral for further management.
If acute pancreatitis occurs, carbimazole should be stopped immediately and permanently.
Thyroid function tests
Refer to endocrinologist if FT4 level falls below reference range or TSH is raised.
Advice to patients
Advise patients to be aware of the symptoms of low white blood cell count. Patients should stop the drug immediately and seek advice if they experience:
- sore throat
- bruising or bleeding
- mouth ulcers
- fever and malaise
Also advise women of childbearing potential to use effective contraception during treatment.
Discontinuation of carbimazole
For adults who have stopped carbimazole, consider measuring TSH (with cascading free T3 and free T4) within 8 weeks of stopping, then every 3 months for a year and then once a year.
- Vanderpump M P, Ahlquist J A, Franklyn J A, et al. Consensus statement for good practice and audit measures in the management of hypothyroidism and hyperthyroidism. The Research Unit of the Royal College of Physicians of London, the Endocrinology and Diabetes Committee of the Royal College of Physicians of London, and the Society for Endocrinology. BMJ. 1996 Aug 31;313(7056):539-44. [cited 30/07/2020]
- UK Guidelines for thyroid function tests by Assoc. Clinical Biochemistry, British Thyroid Assoc and British Thyroid Foundation (Jul 2006) [cited 30/07/2020]
- National Institute for Health and Care Excellence (NICE). Thyroid disease: assessment and management [NG145]. Nov 2019 [cited 31/07/2020]
- Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press [cited 30/06/2020]
- Accord Healthcare Limited. Summary of Product Characteristics – Carbimazole 20mg Tablets (Lime Pharma). Last revised 03/2019 [cited 30/07/2020]
- NICE Clinical Knowledge Summaries (CKS). Hyperthyroidism. Updated Feb 2020 [cited 31/07/2020]
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