Agranulocytosis from antithyroid drugs

What it is

The medical management of hyperthyroidism rests on two main drugs: propylthiouracil (PTU) and methimazole, also written thiamazole (MMI). Both are inhibitors of thyroid hormone synthesis, and PTU on top of that inhibits peripheral de-iodination of T4 to T3. Carbimazole is the one given to most patients with a benign hyperthyroid goiter, with symptomatic treatment added for the palpitations and tremor: beta blockers. The class is called the thionamides.

Agranulocytosis is one of the severe side effects these drugs carry, and it is why the blood count is checked in a patient started on them.

How it presents

The side effects of carbimazole are set out as minor and severe.

• Minor: rash, pruritus, hives, hair loss, nausea, decreased taste, joint pain and arthralgia.
• Severe: agranulocytosis, neutropenia, thrombocytopenia, Stevens-Johnson syndrome, cholestatic jaundice and hepatitis.

A second list of thionamide side effects gives hepatitis, agranulocytosis, fever with arthralgias, rash and vasculitis.

The first sign of agranulocytosis is a sore throat, and it appears 2-3 wks after the drug is started.