It has been found that a commonly-prescribed 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, changing the dosing from 4 weeks to 5-12 weeks reduces the risk for Progressive Multifocal Leukoencephalopathy (PML). PML is a rare but potentially fatal brain infection. 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 hasn't been clear data on whether decreasing dosing frequency improves safety", said first author Lana Zhovtis Ryerson.

Lana continued, "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 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. Patients who test JCV antibody-positive 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, reported safety data through up to 6 years, when the extended dosing regimens were applied, with risk reduction for PML as high as 94 percent.