The US Food and Drug Administration warned health care professionals about the risk of serious liver injury associated with the use of the anti-thyroid drug propylthiouracil (PTU) for the treatment of Graves' disease.

"After analyzing adverse event reports, the FDA has identified an increased risk of liver injury with propylthiouracil when compared to an alternative treatment for Graves' disease, methimazole," said Amy Egan, deputy director for safety, Division of Metabolism and Endocrinology Products, in the FDA's Center for Drug Evaluation and Research. "Health care professionals should carefully consider which drug to initiate in a patient recently diagnosed with Graves' disease. If PTU therapy is chosen, the patient should be closely monitored for symptoms and signs of liver injury, especially during the first six months after initiating therapy."

PTU was approved for marketing in 1947. A total of 32 cases of serious liver injury associated with the use of PTU were reported to the FDA's Adverse Event Reporting System since that system was established in 1969 through October 2008. Of the 22 adult cases, the FDA identified 12 deaths and five liver transplants. Of the 10 paediatric cases, there was one death and six reports of liver transplant.

Graves' disease is an autoimmune disorder that leads to overactivity of the thyroid gland. The thyroid gland, located in the front of the neck just below the Adam's Apple, releases hormones that regulate the rate of the body's metabolism and are critical for body temperature control, energy, weight, mood, and blood calcium levels.

PTU is considered second-line drug therapy, except in certain patients who are allergic to, or intolerant of, methimazole. Because a rare birth defect has been reported with methimazole and not with PTU, PTU may be more appropriate for patients with Graves' disease who are in the first trimester of pregnancy.