Klawiter and Cross, in the journal Neurology, argue that the risk of progressive multifocal leukoencephalopathy (PML) with Tysabri means that we have to examine this much more rigorously. In their paper, entitled The present efficacy of multiple sclerosis therapeutics: is the new 66% just the old 33%? (referring to the supposed better performance of Tysabri in relapse rate reduction than standard DMDs), they argue that because patient populations were markedly different in the trials, with patients with more benign illness in the Tysabri trials, the improved performance of Tysabri may be just an illusion, and it may in fact be comparable in efficacy with the DMDs. Interesting question, and certainly worth debating, given the potentially fatal complication of PML with Tysabri.
There is considerable debate about whether Tysabri actually reduces relapse rate by more than standard DMDs.