TYSABRI clinical trial results:

In a 2-year clinical trial of relapsing MS patients, 627 people were treated with TYSABRI versus 315 with placebo. TYSABRI decreased the number of relapses by 67% compared with placebo (TYSABRI 0.22 vs placebo 0.67).

10 years of results

What is the TYSABRI Observational Program?

In addition to the clinical trial for TYSABRI, it was further studied in the ongoing TYSABRI Observational Program (TOP). We now have the 10-year interim results. 

What was studied?

This analysis studied the long-term safety and efficacy of TYSABRI in 6148 patients with relapsing multiple sclerosis. These patients took 300 mg of TYSABRI every 4 weeks. 

  • These 6148 patients were at different points in their journey, and took TYSABRI for various lengths of time. For example, 3210 people discontinued TYSABRI and the remaining may have not yet reached the end of the 10-year period
  • Patients had 3 or fewer TYSABRI infusions before being enrolled in the study and data were collected from patients at regular doctor visits every 6 months

What are the limitations to the study?

  • This study has limitations and may not be as reliable as a controlled clinical trial. The findings are not included in the full Prescribing Information for TYSABRI
  • Unlike a clinical trial, all observed patients were treated with TYSABRI, so there was no comparison vs placebo
  • Patients participated in countries outside of the United States, so results may not have been the same in the United States

What was discovered?


Findings were consistent with the previous studies of TYSABRI for up to 10 years of treatment.

  • 13.5% (829 of 6148 patients) experienced at least 1 serious adverse event. The most common were infection and infestations (PML, pneumonia, urinary tract infection, and herpes zoster) with an incidence of 4.1%
  • 4.7% (290 of 6148 patients) had at least 1 serious treatment-related side effect


reduction in average number of relapses in the first year of the study,* and the reduction remained the same through all 9 years

*Compared to average number of relapses in the year before they started TYSABRI (1.99 vs 0.24).