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carbimazole

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carbimazole

Introduction

  • carbimazole is the first line thionamide in almost all patients with hyperthyroidism needing Rx with an antithyroid medication as it results in a more rapid improvement in thyroid hormone levels, has less hepatotoxicity, and can be given once daily due to its longer half life

Dose

  • starting dose of carbimazole is 10–30 mg/day in 2–3 divided doses depending on severity of thyrotoxicosis, although larger doses may be used in severe disease
  • Four weeks following initiation of therapy, clinical review with repeat thyroid function tests should be undertaken to avoid hypothyroidism
  • Antithyroid drug therapy is tapered to a maintenance dose (usually carbimazole 2.5–10 mg) and ceased after 12–18 months of therapy
  • patients should be warned to see a doctor if either:1)
    • fever, mouth ulcers, sore throat or other symptoms suggestive of infection (suspend drug and urgently report to obtain neutrophil count)
    • severe fatigue, nausea, abdominal pain, jaundice, dark urine or pale stools (suspend drug and urgently report for investigation)
    • rash - could it be vasculitis?
    • arthralgia

Adverse effects

  • relatively common effects:
    • Gastrointestinal effects (nausea, vomiting, gastric discomfort)
    • Rash (urticarial or macular)
    • arthralgia or fever - may be a sign of more serious effects so generally cease Rx
    • transient mild neutropenia
  • agranulocytosis (neutrophil count <0.5×109/L) is a rare but life-threatening complication of both antithyroid drugs with an incidence of 0.2–0.5% and due to cross reactivity between the two antithyroid medications, agranulocytosis with one drug is an absolute contraindication to trialling the other
  • cholestatic hepatitis
  • Polyarthritis
  • ANCA-positive vasculitis
  • use in pregnancy
    • carbimazole during pregnancy has been associated with birth defects, including aplasia cutis and 'carbimazole embryopathy', characterised by choanal atresia or oesophageal atresia.
    • it is usually recommended that propylthiouracil be used in the first trimester and then changed to carbimazole in the second trimester 2)
  • other effects see documentation
carbimazole.txt · Last modified: 2020/01/27 17:19 (external edit)