Hepatotoxicity from antithyroid drugs

We review the cases of hepatic injury from propylthiouracil, methimazole and carbimazole in the English language literature and compare them to cases of agranulocytosis in a recent review. The data on hepatotoxicity confirm the findings for agranulocytosis that low-dose methimazole is safer than propylthiouracil and that methimazole toxicity is more common over 40 years old. In contrast, propylthiouracil hepatotoxicity often occurs in younger patients. Most cases of hepatic injury occur in the first few months of drug therapy as with agranulocytosis. The reason that methimazole typically causes cholestatic hepatitis while propylthiouracil causes cytotoxic hepatitis remains unknown.