The government is warning that taking the psoriasis drug Raptiva could result in serious brain infection and even death. The Food and Drug Administration cited three confirmed cases, and a possible fourth, of people diagnosed with progressive multifocal leukoencephalopathy (PML) after being treated with Raptiva. "Three of those patients have died," the FDA said in a public health advisory. "All four patients were treated with the drug for more than three years." None was receiving other treatments that suppress the immune system. Raptiva, a once-weekly injection for adults with moderate to severe plaque psoriasis, works by suppressing T-cells -- cells that help fight infection -- in the immune system. Those cells cause the skin inflammation associated with psoriasis.

Raptiva's product labeling was revised in October to highlight a boxed warning about the risks of life-threatening infections, including PML. "At that time, the FDA directed Genentech, the manufacturer, to develop a risk evaluation and mitigation strategy (REMS) to include a medication guide to educate patients about the drug's risks," the FDA's advisory says. In the advisory, issued Thursday, the FDA highlighted the confirmed cases and promised to "take appropriate steps" to ensure that Raptiva's risks do not outweigh its benefits.

Learn more about dangerous Raptiva side effects.