From the Guidelines
Yes, it is contraindicated to trial propylthiouracil (PTU) in a patient with a history of carbimazole-induced agranulocytosis. These medications share cross-reactivity, and a patient who has experienced agranulocytosis with carbimazole has a high risk of developing the same potentially life-threatening reaction with PTU. Agranulocytosis is characterized by severely decreased neutrophil counts, leaving patients vulnerable to serious infections. The cross-sensitivity between thionamide drugs (carbimazole, methimazole, and PTU) is well-established, with estimates suggesting a high chance of similar reactions occurring with alternative thionamide medications 1.
Key Considerations
- Agranulocytosis is a serious side effect of thioamides, usually presenting with sore throat and fever, and requires immediate discontinuation of the medication and a complete blood cell count 1.
- The goal in managing hyperthyroidism in patients with a history of carbimazole-induced agranulocytosis is to maintain euthyroidism while minimizing the risk of recurrent agranulocytosis.
- Alternative treatment options for hyperthyroidism should be pursued instead, including radioactive iodine therapy or thyroidectomy.
- In urgent situations where thyroid hormone levels must be controlled while arranging definitive therapy, non-thionamide medications such as beta-blockers, corticosteroids, and cholestyramine may be used for symptomatic management.
Management Approach
- Avoid the use of PTU in patients with a history of carbimazole-induced agranulocytosis due to the risk of cross-reactivity and recurrent agranulocytosis.
- Consider alternative treatments for hyperthyroidism, such as radioactive iodine therapy or thyroidectomy, in consultation with an endocrinologist.
- Use non-thionamide medications for symptomatic management in urgent situations, with close monitoring of the patient's condition and laboratory parameters.
From the Research
Propylthiouracil (PTU) Contraindication in Patients with Carbimazole (Methimazole) Induced Agranulocytosis
- The use of PTU is contraindicated in patients with a history of carbimazole (methimazole) induced agranulocytosis, as it is possible for these patients to have the same complication with PTU 2.
- Agranulocytosis is a rare but serious complication of antithyroid drugs, including methimazole and PTU, and can be life-threatening if not promptly diagnosed and treated 3, 4.
- Patients who develop agranulocytosis with one antithyroid drug may be at risk of developing it with another, highlighting the need for careful monitoring and alternative treatment options 5, 2.
- In cases of methimazole-induced agranulocytosis, treatment with PTU is not recommended, and alternative treatments such as saturated solution of potassium iodide (SSKI), beta-blockade, cholestyramine, and granulocyte colony stimulating factor may be considered 3.
- The incidence of agranulocytosis due to antithyroid drugs is relatively rare, but it is a potentially serious complication that requires prompt attention and treatment 6.