From the Guidelines
Carbimazole can cause several serious side effects, including agranulocytosis, hepatitis, vasculitis, and thrombocytopenia, which can be life-threatening and require immediate medical attention. Although the provided study 1 does not directly mention carbimazole, it discusses the side effects of thioamides, a class of medications that includes carbimazole. According to the study, agranulocytosis, a side effect of thioamides, usually presents with sore throat and fever, and if these symptoms develop, a complete blood cell count should be obtained, and the thioamide should be discontinued. Other side effects mentioned in the study include hepatitis, vasculitis, and thrombocytopenia.
Common Side Effects
- Nausea
- Mild skin rashes
- Itching
- Headaches
- Joint pain
- Altered taste sensation
Serious Side Effects
- Agranulocytosis (severe reduction in white blood cells)
- Liver inflammation (hepatitis)
- Vasculitis (blood vessel inflammation)
- Thrombocytopenia (reduced blood platelet counts) It is essential to monitor patients regularly with blood tests, especially during the first months of treatment, and inform healthcare providers immediately if experiencing fever, sore throat, unusual bleeding or bruising, yellowing of the skin or eyes, or severe skin reactions, as these can be signs of serious side effects 1.
From the Research
Side Effects of Carbimazole
The side effects of carbimazole, an antithyroid medication, can be categorized into common and rare adverse reactions.
- Common side effects include:
- Dose-dependent hypothyroidism, which requires repeated thyroid function checks while on the medication 2
- Pruritus and rash, which may necessitate switching to an alternative antithyroid drug like propylthiouracil 2
- Mild dose-dependent neutropenia 2
- Arthralgias, which may develop in 1-5% of patients and could be a symptom of more serious immunologic side effects 2
- Rare but serious side effects include:
- Severe allergy-mediated agranulocytosis, typically occurring within the first three months of treatment, with an incidence of 3 per 10,000 patients 2
- Aplastic anemia 2
- Asymptomatic transient increase in liver enzymes or severe liver injury of cholestatic or hepatocellular pattern, more commonly associated with propylthiouracil but also possible with methimazole (the active metabolite of carbimazole) 2, 3, 4, 5, 6
- Drug-induced polyarthritis and ANCA-positive vasculitis, more commonly observed with long-term exposure to propylthiouracil but can also occur with thioimidazoles like carbimazole 2
- Teratogenic effects, such as aplasia cutis congenita, which may be more significant with thioimidazoles, leading to a preference for propylthiouracil during pregnancy 2
Management of Side Effects
In cases of side effects, management strategies may include:
- Discontinuation of carbimazole and potential switching to an alternative antithyroid drug like propylthiouracil 2, 3
- Administration of granulocyte colony-stimulating factor for severe neutropenia 4, 5
- Supportive treatment and monitoring for resolution of symptoms and laboratory abnormalities 3, 4, 5, 6