6.2.2 Antithyroid drugs

Neutropenia and agranulocytosis

Doctors are reminded of the importance of recognising bone marrow suppression induced by carbimazole and propylthiouracil, and the need to stop treatment promptly.

  1. Patients should be asked to report symptoms and signs suggestive of infection, especially sore throat, mouth ulcers and high fever
  2. A white blood cell count should be performed if there is any clinical evidence of infection
  3. Carbimazole should be stopped promptly pending results of clinical or laboratory evidence of neutropenia
  • Tablets 5mg, 20mg (£62.37 = 100 x 5mg)



  • 15 to 40mg daily; higher doses should be prescribed under specialist supervision only. This dose is continued until the patient becomes euthyroid, usually after 4 to 8 weeks and the dose is then gradually reduced to a maintenance dose of 5 to 15mg. Therapy is usually given for 12 to 18 months


  1. MHRA Drug Safety Update (February 2019): Carbimazole: increased risk of congenital malformations; strengthened advice on contraception
    1. Carbimazole is associated with an increased risk of congenital malformations when used during pregnancy, particularly in the first trimester of pregnancy and at high doses (15 mg or more of carbimazole daily)
    2. Women of childbearing potential should use effective contraception during treatment with carbimazole
    3. Carbimazole should only be considered in pregnancy after a thorough individual assessment of benefits and risks of treatment, and only at the lowest effective dose without additional administration of thyroid hormones; close maternal, foetal, and neonatal monitoring is recommended
  2. See resources for: contraception for drugs with teratogenic potential, and prescribing in pregnancy and lactation
  3. MHRA Drug Safety Update (February 2019): Carbimazole: risk of acute pancreatitis
    1. Cases of acute pancreatitis have been reported very infrequently during treatment with carbimazole
    2. If acute pancreatitis occurs, stop carbimazole treatment immediately
    3. Do not use carbimazole in patients with a history of acute pancreatitis in association with previous treatment
    4. Re-exposure may result in life-threatening acute pancreatitis with a decreased time to onset
  • Tablets 50mg (£59.47 = 56 tablets)



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