The US Food and Drug Administration (FDA) are warning health care professionals about the risk of serious liver injury linked to the anti-thyroid drug propylthiouracil that is used to treat Graves' disease, an autoimmune disorder that results in overactivity of the thyroid gland.

The FDA posted a warning on its website on 3 June that says the agency has received reports of 32 cases of serious liver injury associated with the use of propylthiouracil, a drug that was approved for marketing in 1947.

22 of the cases were in adults, and these included 12 deaths and 5 liver transplants, said the FDA.

10 cases were in children, including one death and six liver transplants.

The reports came through the FDA's Adverse Event Reporting System which was established in 1969 and cover the period from then until 2008. The warning came after the FDA analyzed adverse event reports in the system.

Dr Amy Egan, deputy director for safety, Division of Metabolism and Endocrinology Products, in the FDA's Center for Drug Evaluation and Research explained:

"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."

Graves' disease causes the thyroid, a gland that sits just under the Adam's apple at the front of the neck, to become overactive. The thyroid releases hormones that help to control metabolism, body temperature, energy use, weight, mood, and the amount of calcium in the blood.

"Health care professionals should carefully consider which drug to initiate in a patient recently diagnosed with Graves' disease," said Egan, adding that:

"If propylthiouracil 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."