Assessing long-term drug safety: lessons (re) learned from raptiva.

Efalizumab was approved for moderate to severe psoriasis in 2003 based on studies in approximately 2700 patients, of whom only 218 were exposed to the drug for more than 1 year. In 2009, after more than 46,000 patients were exposed to efalizumab, the drug was withdrawn from the market after 3 confirmed and 1 suspected case of progressive multifocal leukoencephalopathy (PML) were spontaneously reported. As PML is very rare, it is extremely unlikely that the 4 reported cases were due to chance and given that PML occurs primarily in patients who are immunosuppressed, the association is likely causal. The identification of PML as a serious, but statistically rare risk of efalizumab demonstrates the strengths and weaknesses of the current drug approval and pharmacovigilance processes for fully measuring the safety of a drug. Patients and clinicians need to be aware of the relative completeness and limitations of existing safety data of a drug when selecting a treatment.