You can take Tysabri for as long as you want providing you tolerate it well, have not developed any serious side effects, and Tysabri is still preventing relapses if you have multiple sclerosis (MS) or reducing symptoms, if you have Crohn’s disease. For people with MS, some response is noted at 12 weeks, but it may take up to 2 years for the full effects to be seen. People with Crohn’s disease should discontinue Tysabri if there is no benefit after 12 weeks.

Recently the results of a 10-year observational study investigating the long-term benefits of Tysabri in MS were reported.

• An 88% reduction in the number of relapses during the first year of the study was reported, which persisted through all 9 years. The number of relapses went from an average of 1.99 in the year before starting Tysabri to 0.24 the year after starting treatment.
• 6148 people with relapsing MS started the study and 3210 people discontinued Tysabri during the study. The dosage was 300mg of Tysabri every 4 weeks.
• 13.5% (829 of 6148 patients) experienced at least 1 serious adverse event. Infections (such as progressive multifocal leukoencephalopathy [PML], pneumonia, urinary tract infection, or herpes zoster) accounted for 4.1% of these adverse events.
• 4.7% (290 of 6148 patients) had at least 1 serious treatment-related side effect, such as an allergic reaction.

Tysabri may be used to treat adults with multiple sclerosis or Crohn's disease and is given once every four weeks through an infusion center registered with the Touch Prescribing Program. A headache, fatigue, joint pain, and infections are the most common side effects reported although rarely, it may cause more serious side effects such as liver failure, severe herpes infections, or PML. It may not be suitable for people who already have a weakened immune system.