A commonly-prescribed multiple sclerosis (MS) infusion medication  Natalizumab  linked to a rare but serious side effect is safer to use when dosing intervals are extended, according to a new study led by MS specialists NYU Langone Health .

The new research Showed That Extending from dosing of natalizumab every 4 weeks to every 5 to 12 weeks Significantly reduced the risk of developing progressive multifocal leukoencephalopathy (PML), a rare but fatal brain infection Potentially.

"Neurologists have been looking for safer ways to administer natalizumab infusions to their patients, but there has been no clear data on whether there is a decrease in the rate of safety," said Lana Zhovtis Ryerson, assistant professor of neurology at NYU School of Medicine .

"Our safety findings are clinically and statistically significant, and we believe that extending the dosing schedule of natalizumab is practice changing and may save lives," Ryerson said.

Natalizumab, a monoclonal antibody , is used to prevent MS relapses, improve quality of life, and slow worsening disability. The medication is indicated to be prescribed in 300-milligram infusion doses every 4 weeks.

Taking the medication longer than two years, however, may increase risk PML, which is caused by the John Cunningham virus (JCV). There have been 756 PML cases reported worldwide as of January 2018, with a global incidence rate of 4.19 per 1,000 PML cases in people treated with natalizumab.

The new study, however, reports safety data through up to 72 months , or 6 years, when the extended dosing regimens were applied, with risk reduction for PML as high as 94 percent .

Researchers reviewed data on the patients who have been exposed to JCV who are enrolled in TOUCH, the US Food and Drug Administration and the Risk Evaluation and Mitigation Strategy (REMS) program for natalizumab that requires manufacturers to document all uses of a medication to ensure that the benefits of a drug outweigh its risks.

Researchers looked at the data in multiple ways, with the primary definition with extended dose history in the last 18 months, the secondary definition with extended dose occurring at any time in the dosing history, and for tertiary definition with how extended dose history affects PML risk . The results showed significant risk reductions with all definitions.

Previous research led by Dr. Zhovtis-Ryerson's group found to be up to 8 weeks ago did not negatively affect the medication's efficacy in a retrospective sample of 2,000 people. The authors are planning prospective efficacy studies of extended dose natalizumab.

Natalizumab is manufactured by Biogen Idec and Elan, and sold under the name Tysabri®. Biogen provided by the researchers access to their data and statistical support. Other infusion disease-modifying therapies approved to treat MS include the drugs alemtuzumab and ocrelizumab. Oral and injectable medications are also prescribed.