The Food and Drug Administration (FDA) has added a black box warning to the label of propylthiouracil, a drug used to treat hyperthyroidism. The warning states that severe liver injury and acute liver failure (which has resulted in fatalities in some cases) have occurred in some adult and pediatric patients who received the drug. Between 1969 and 2009, 34 cases of severe liver damage were reported to the FDA. The creation of the black box warning was a follow-up to the June 2009 Information for Healthcare Professionals issued by the FDA that warned of this possible adverse event.

The black box warning states that in patients newly diagnosed with hyperthyroidism and requiring drug therapy, propylthiouracil should be reserved for those who cannot tolerate methimazole (the other approved antithyroid medication), radioactive iodine therapy, or surgery. Methimazole has also been the subject of a few reports of severe liver injury, but the FDA has concluded that propylthiouracil carries a higher risk of serious liver damage.

Unlike propylthiouracil, methimazole has been associated with fetal craniofacial malformations when used during the first trimester of pregnancy; propylthiouracil should therefore be used as first-line therapy if the patient is trying to become pregnant or is in the first trimester of pregnancy. Nurses should teach patients who've been prescribed propylthiouracil to be alert for signs of liver toxicity, such as loss of appetite, nausea, vomiting, tiredness, itchy skin, jaundice, and dark tea-colored urine, and to notify their prescriber if these signs or symptoms occur. Nurses should also instruct patients to read the medication guide accompanying each prescription for information on possible adverse effects. For more information from the FDA, go to http://bit.ly/bGjBOU.