The FDA’s scheduled March 29 decision on Biogen Idec and Elan’s Tysabri will be delayed by as much as 90 days, the drug makers said this week.An FDA advisory panel ruled unanimously March 9 that Biogen Idec’s multiple sclerosis drug Tysabri should return to the market with safeguards to monitor patient complications. Tysabri marketers pulled the drug in February 2005 after two patients developed progressive multifocal leukoencephalopathy, or PML, a rare and often fatal brain infection. A third patient was later discovered to have PML. Two of the three patients died.