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Propylthiouricil

posted Jun 16, 2010, 6:15 PM by Medhavi Jogi

The United States Food and Drug Administration (FDA) has added a Boxed Warning to the label for propylthiouracil (PTU), a drug used to treat hyperthyroidism, to include information about reports of severe liver injury and acute liver failure, some of which have been fatal, in adult and pediatric patients using this medication. Approximately 15,000 adults are, therefore, estimated to begin PTU therapy per year. If the frequency of PTU-related severe liver damage is approximately 0.1% in adults, based on available data, approximately 15 adults will develop related severe hepatic injury annually in the United States. If 10% of these individuals develop liver failure resulting in liver transplantation or death (1:10,000 incidence), each year one or two individuals with Graves’ disease in the United States will die or require a liver transplant after PTU exposure

The new, official warning also states that for patients being started on treatment for hyperthyroidism it may be appropriate to reserve use of propylthiouracil for those who cannot tolerate other treatments for hyperthyroidism. These other treatments for hyperthyroidism include such as methimazole, radioactive iodine or surgery. 

Indications for PTU are:

  1. Pregnant women during their first trimester  or just prior to the first trimester (where the risk of methimazole-associated birth defects might outweigh the risks of PTU).  There are 4 million births per year in the United States, and with a 0.1% frequency of Graves’ disease in pregnancy, approximately 4000 women per year would be expected to be treated with antithyroid drugs. Most of them would be treated with PTU, per current practice guidelines. Consequently, it can be estimated that four women per year will have severe PTU-related hepatic complications, based on generally reported rates of severe liver injury in adults, although no pregnancy-specific data are available.
  2. Patients with life-threatening thyrotoxicosis or thyroid storm (because of PTU's ability to inhibit peripheral conversion of T4 to T3)
  3. Patients with adverse reactions to MMI (other than agranulocytosis) who are not candidates for radioiodine or surgery.


References:

Bahn, RS, Burch, HS, Cooper, DS, et al. The Role of Propylthiouracil in the Management of Graves' Disease in Adults: report of a meeting jointly sponsored by the American Thyroid Association and the Food and Drug Administration. Thyroid 2009; 19:673.

Cooper, DS, Rivkees, SA. Putting propylthiouracil in perspective. J Clin Endocrinol Metab 2009; 94:1881.



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