Tysabri, which is primarily a treatment for patients with multiple sclerosis (MS),  was returned to the US market last July. It had been withdrawn in Feb 2005 after adverse results involving a small number of patients who had developed a rare brain disease

Irish drugs firm Elan Corporation and US biotech company Biogen Idec announced today data that show Tysabri (natalizumab) maintained remission in Crohn's disease patients (CD) treated for longer than 2 years.

These data, presented this week at the 14th United European Gastroenterology Week (UEGW) in Berlin, Germany, and at the Annual American College of Gastroenterology (ACG) in Las Vegas, Nevada, were part of an open label extension study of patients who participated in the ENACT-2 trial.

Ninety-three percent (93%) of Tysabri patients who were in remission at month 12 of ENACT-2, were still in remission following 6 additional Tysabri infusions in the open-label extension study (OLE) and 86% were still in remission after 12 additional infusions.

These results were based on approximately 90 patients who were in remission after 15 months of continuous Tysabri therapy in the ENACT-1 and ENACT-2 trials and elected to enroll in an open-label extension trial. A subpopulation of 22 patients was previously exposed to infliximab therapy. In this subpopulation, 91% were in remission after additional 6 and 12 infusions of Tysabri, and 82% who had previously failed therapy with infliximab were in remission at the same time points.

"What is truly exciting is that patients who enter remission on Tysabri may remain in remission in the long-term without loss of efficacy over time. These data are a significant advance for the field and suggest that Tysabri may be an alternative biologic outside the anti-TNF class for patients suffering from Crohn's disease," said Remo Panaccione MD, Director, Inflammatory Bowel Disease Clinic, University of Calgary, Calgary, Canada, who presented the data at UEGW.

Incidence of adverse events (AE's) and infection was similar to CD clinical trials, in which most common adverse events were headache, nausea, nasopharyngitis, and abdominal pain. In short-term controlled studies in CD, the incidence of serious infection was comparable between Tysabri and placebo treatment groups. In longer-term, open-label clinical trials, one case of progressive multifocal leukoencephalopathy (PML) was observed.

ENACT-2 OLE Study Trial Design

Patients who completed the ENACT-2 trial were eligible to enroll in an open-label extension study. The primary objective of the two-year OLE study was to examine the long-term safety and tolerability of Tysabri. Secondary efficacy endpoints included evaluation of the ability of Tysabri to maintain remission. This analysis included patients who were in remission after 15 months of continuous Tysabri therapy in both ENACT-1 and -2 trials and elected to enroll in the OLE study and receive additional Tysabri therapy. Approximately 90 patients met the criteria for analysis, 22 of which had previous exposure to anti-TNF. Remission rates were calculated using last observation carried forward.