The Department of Health warns of the risk of severe or even fatal liver damage from drugs containing propylthiouracil, a pharmaceutical agent used to treat hyperthyroidism.

The US Food & Drug Administration said yesterday due to severe, sometimes fatal, liver injury reports in people using propylthiouracil, or PTU, the addition of a boxed warning to the label for PTU is required to help patients understand the serious risk.

It had identified 34 severe liver injury cases, comprising 23 adults and 11 paediatric patients. Of the former, 13 died and five had liver transplants. Two fatalities and seven transplants were noted in the children's group, and one died while on the transplant list.

In Hong Kong five drugs with PTU - CP-PTU 50mg Tablet (HK-47993), Pyroid 50mg Tablet (HK-59451), Propylthiouracil 200mg Tablet (HK-04961), Propylthiouracil 50mg Tablet (HK-04990) and Propylthiouracil 50mg Tablet (HK-07500) - are registered with the Pharmacy & Poisons Board. They can only be sold in dispensaries on a doctor's prescription and under a pharmacist's supervision.

The surveillance finding has been referred to the board's Registration Committee, which will review the registration requirements for PTU at its next meeting.

The department advises people using drugs containing PTU to consult their doctors should they encounter problems. However, they must not stop taking PTU unless they have been told to do so by their doctor.

Known side effects of PTU include encephalopathy and liver damage ranging from asymptomatic to hepatitis to necrosis.