The removal of Tysabri from the market soon after its introduction is expected to increase scrutiny of other similar drugs in development for multiple sclerosis (MS), says ECRI, a leading, independent health services research agency.
Tysabri, one of a handful of monoclonal antibodies (MAbs) under study as a drug that would modulate the immune system, was approved for marketing in November 2004 under the U.S. Food and Drug Administration's (FDA) accelerated approval process. It was indicated as a treatment for relapsing MS. However, the drug was pulled off the market in early 2005 because in clinical trials there were two confirmed cases (one fatal) of progressive multifocal leukoencephalopathy (PML), a rare and frequently fatal nervous system disorder. In an effort to better understand the risks of PML, the drug's manufacturers (Biogen Idec and Elan Corporation) state that they are consulting leading experts. The outcome of these discussions will be used to determine possible re-initiation of dosing in clinical trials and future commercial availability, according to the companies.
In its Health Technology Forecast, an online horizon-scanning resource for healthcare executives and technology planners, ECRI recognizes that even if Tysabri returns to the market, its potentially fatal effects may temper a physician's willingness to prescribe it. ECRI also predicts that recent concerns raised over the safety of other FDA-approved drugs that were withdrawn from the market may dampen utilization of this drug if it returns to the market.
However, ECRI predicts that if MAbs do eventually prove safe for treating MS, they will be of great interest for other applications because they can be used to specifically target disease organisms and other types of molecules found in the body such as hormones, infectious substances, toxins, and proteins on the surface of normal cells or those uniquely present on the surface of cancer cells.