FDA Warning About Thyroid Drug Propylthiouracil / PTU

Black Box Warning Recommends Limits on Use of PTU

Doctor explaining prescription medication to patient in clinic
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Propylthiouracil -- also known as PTU -- came into use in 1947 as an antithyroid drug to treat hyperthyroidism. PTU and methimazole -- which also goes by the brand name Tapazole -- are the two antithyroid drugs available in the US to treat hyperthyroidism.

In 2010, the US Food and Drug Administration (FDA) added what's known as a "black box" warning to the label for PTU. Based on identification of several dozen cases of severe liver injury, including death, associated with use of PTU in adults and children, the FDA determined that use of propylthiouracil is associated with a higher risk for clinically serious or fatal liver injury compared to methimazole.

The FDA's warning does indicate that PTU may be appropriate to use in two specific situations:

  • When a patient cannot tolerate the other antithyroid drug treatment such as methimazole (Tapazole), or other treatments for hyperthyroidism, such as radioactive iodine (RAI) or thyroid surgery. The FDA says that PTU should not be administered to children unless the child is allergic to or unable to tolerate methimazole, and other treatment options are not available.
  • When a woman is in the first trimester of pregnancy-- because there is an increased risk of birth defects in babies whose mothers have taken the thyroid drug methimazole during the first trimester of pregnancy. Experts typically recommend that after the first trimester of pregnancy, a woman should switch back to methimazole. 

If you are taking PTU, the FDA recommends that your doctor monitor you for signs and symptoms of liver injury, particularly during the first 6 months after beginning treatment.


Additional Information for Patients

The following is the FDA's "Additional Information for Patients" regarding PTU:

  • Be aware that severe liver injury has occurred in patients taking propylthiouracil.
  • Read the Medication Guide when picking up a prescription for propylthiouracil. It will help you understand the potential risks and benefits of this medication.
  • Contact your healthcare professional if you have fever, loss of appetite, nausea, vomiting, tiredness, itchiness, dark colored urine, or yellowing of your skin or eyes while taking propylthiouracil.
  • Propylthiouracil may be the treatment of choice during and just before the 1st trimester of pregnancy (weeks 1-12). Talk to your healthcare professional if you are pregnant (or plan to become pregnant) and are taking a medication to treat hyperthyroidism.
  • Tell your healthcare professional about any medication you are taking or medical conditions you may have before taking propylthiouracil.
  • Do not stop taking propylthiouracil unless told to do so by your healthcare professional.

Additional Information for Healthcare Professionals

The following is the FDA's "Additional Information for Healthcare Professionals" regarding PTU:

  • Be aware that severe liver injury and acute liver failure, including fatal cases, have been reported in adult and pediatric patients taking propylthiouracil.
  • When initiating hyperthyroid treatment, propylthiouracil should be reserved for patients who cannot tolerate methimazole or for patients for whom radioactive iodine therapy or surgery is not appropriate treatment.
  • Propylthiouracil may be the treatment of choice when an antithyroid drug is needed during and just prior to the 1st trimester of pregnancy. Fetal abnormalities have been seen with methimazole use during the first trimester of pregnancy.
  • Propylthiouracil is not recommended for use in pediatric patients, except in rare instances in which other alternative treatments are not appropriate.
  • Encourage patients to read the Medication Guide when picking up their prescription for propylthiouracil.
  • Review the newly revised label for complete information on the use of propylthiouracil.

Read the FDA's PTU Medication Guide

You can read the full "Medication Guide" for PTU at the FDA's site, in PDF format here.

Source: FDA Drug Safety Communication: New Boxed Warning on severe liver injury with propylthiouracil, 04-21-2010

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