The manufacturer of a drug that treats psoriasis has issued new safety information for doctors and patients.

EMD Serono Canada says Raptiva has been associated with a risk of serious infections, including progressive multifocal leukoencephalopathy, a rare and sometimes fatal brain disorder.

Raptiva suppresses the body's immune response to reduce psoriasis inflammation; however, the company says that by diminishing the body's natural defence system, it can also increase the risk of serious infections in some patients.

Signs and symptoms of PML may include difficulty thinking, walking or speaking, or other behavioural changes, weakness, loss of balance or co-ordination, visual impairment, partial paralysis of one side of the body, or seizures.

Other serious infections may be indicated by fever, weakness, cough, flu-like symptoms, warm, red or painful skin, or open sores on the body.

If people taking Raptiva develop any of these symptoms, they should contact their health-care professional, the drugmaker said, but they shouldn't change or stop treatment without first speaking to the doctor.

The company said infections — some serious and leading to hospitalizations or deaths — have been observed in patients treated with Raptiva, also known as efalizumab.

PML occurs almost exclusively in people with severe immune deficiency, said the Serono Canada statement posted on Health Canada's website.

Two deaths from PML have been reported in the United States in patients who were being treated with Raptiva for longstanding psoriasis.

Both cases occurred in patients aged 70 or older who received Raptiva continuously for approximately four years. One of the affected patients had also received another medication that suppresses the immune system for a short time, three years prior to the diagnosis of PML.

The patients were diagnosed with PML about four years after starting Raptiva.

A direct cause and effect between Raptiva and the infections hasn't been established, but cannot be ruled out, the company said.

Prescribing information for Raptiva will be revised in Canada to include more information on serious infections including PML.

In October, the U.S. Food and Drug Administration announced that Raptiva would begin carrying a black box warning — the most serious kind — about the risk of life-threatening infections, including PML.

In early December, the Ontario Public Drug Program, which provides coverage for seniors, residents in long-term and special-care homes, cancer patients and others, said it was adding Raptiva to its list of insured drugs.

The drug company estimates that about 46,000 patients have been treated with Raptiva worldwide since it was first authorized.

Adverse reactions should be reported to EMD Serono Canada Inc. or Health Canada.