Table 4.

Key events surrounding withdrawal and reintroduction of Tysabri

Product	Year	Event
Tysabri	2004	FDA approves Tysabri (natalizumab) for relapsing-remitting Multiple Sclerosis (RRMS)
	2004	Biogen reports 3 cases, 1 fatality, of progressive multifocal leukoencephalopathy (PML)
	2005	Tysabri withdrawn from the market
	2006	Clinical trial participants tested for PML; safety data gathered and reviewed by drug sponsor and FDA
	2006	FDA studies evidence, recommends Tysabri reintroduced via restricted distribution program “TOUCH”
	Post-2006	Analyses of TOUCH data, clinical trial data, and continued research help clarify risk of PML; Health care providers have risk model to quantify and rank vulnerability to PML for patients
	Post-2006	Physicians and patients know more about the risk of PML to Tysabri; The number of patients on Tysabri remains well short of expectations.