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Multiple Sclerosis Health Center

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MS Drug: No More Rare Disease Cases

Researchers Find No New Cases of PML During Tysabri Drug Trial
WebMD Health News
Reviewed by Louise Chang, MD

March 1, 2006 -- Researchers have found no new cases of a rare disease in patients who took the multiple sclerosis drug Tysabri before the drug's suspension last year.

The FDA approved Tysabri in November 2004 to treat relapsing forms of multiple sclerosis (MS). On Feb. 28, 2005 Tysabri was suspended over cases of a rare, disabling neurological disease called PML in patients taking Tysabri.

In February 2006 the FDA allowed Tysabri's clinical trials for MS treatment to resume. However, the drug isn't back on the market.

PML, or progressive multifocal leukoencephalopathy, affects the central nervous system, usually in people with unhealthy immune systems. PML is caused by a common virus, but most people with the virus don't get PML.

Now, researchers say they've found no new cases of PML in more than 3,000 patients who took Tysabri in the drug's clinical trials. Their report appears in The New England Journal of Medicine.

Combing the Records

The researchers did a detailed review of 3,116 patients who took Tysabri in clinical trials. Most patients had gotten nearly 18 monthly doses of the drug. The patients either had MS, Crohn's disease, or rheumatoid arthritis. Before its suspension, Tysabri was being studied as a possible treatment for Crohn's disease and rheumatoid arthritis.

The patients got medical exams, brain scans using magnetic resonance imaging (MRI), and a test of cerebrospinal fluid to check for the virus that causes PML. Their medical records were also examined.

A total of 44 patients were referred to experts to check for possible PML. All but one of those patients turned out not to have PML. Complete data wasn't available for the one exception, so PML wasn't confirmed in that person, either.

The only confirmed cases of PML in people taking Tysabri are the three cases that had previously been reported, according to the review.

Review's Conclusions

The review had three key findings:

  • The group had no new cases of PML.
  • About one in 1,000 trial participants who took Tysabri for 18 months got PML.
  • PML risk beyond 18 months isn't known.

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