"A commonlyprescribed multiple sclerosis MS infusion medication 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 dosing of natalizumab from every  weeks to every  to  weeks significantly reduced the risk of developing progressive multifocal leukoencephalopathy PML a rare but potentially fatal brain infection. The authors presented their findings February  at the Americas Committee for Treatment and Research in Multiple Sclerosis ACTRIMS Forum  in San Diego. The findings could influence how neurologists prescribe the medication. Neurologists have been looking for safer ways to administer natalizumab infusions to their patients but there hasnt been clear data on whether decreasing dosing frequency improves safety says first study author Lana Zhovtis Ryerson MD httpsnyulangone.orgdoctorslanazhovtisryerson assistant professor of neurology at NYU School of Medicine and an attending neurologist at NYU Langones Multiple Sclerosis Comprehensive Care Center httpsnyulangone.orglocationsmultiplesclerosiscomprehensivecarecenter. 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. 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 milligram infusion doses every  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  PML cases reported worldwide as of January  with a global incidence rate of . per  PML cases in people treated with natalizumab. Patients who test JCV antibodypositive are typically either told to not to start natalizumab or have had treatment stopped after two years when risk was deemed to be too high. The new study however reports safety data through up to  months or  years when the extended dosing regimens were applied with risk reduction for PML as high as  percent.  How the Study Was Conducted Researchers reviewed data on all patients who have been exposed to JCV who are enrolled in TOUCH the U.S. Food and Drug Administrationmandated 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. Since the optimal extended dose schedule is not known researchers chose to look at the data in multiple ways with the primary definition looking at extended dose history in the last  months the secondary definition looking at extended dose occurring at any time in the dosing history and for tertiary definition looking primarily at how extended dose history affects PML risk. The results showed clinically and statistically significant risk reductions with all definitions.  The new study did not look at drug efficacy comparing extended to standard doses. However previous research led by Dr. ZhovtisRyersons group found extending the dose up to  weeks did not negatively affect the medications efficacy in a retrospective sample of  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 the researchers access to their data and statistical support.  Other infusion diseasemodifying therapies approved to treat MS include the drugs alemtuzumab and ocrelizumab. Oral and injectable medications are also prescribed.  The study was carried out in collaboration with Biogen and academic collaborators from NYU School of Medicines Division of Biostatics University of Alabama at Birmingham School of Medicine and Rocky Mountain Multiple Sclerosis Clinic in Utah.  In addition to Dr. ZhovtisRyerson Ilya Kister MD associate professor of neurology Judith D. Goldberg professor of population health and environmental medicine and Xiaochun Li PhD research scientist of biostatistics were coauthors at NYU Langone Health. Other coauthors include Dr. John Foley Dr. Ih Chang Professor Gary R. Cutter Dr. Ryan Metzger Dr. Evan Riddle Dr. Bei Yu Dr. Zheng Ren Dr. Christophe Hotermans Dr. PeiRan Ho and Dr. Nolan Campbell."