Genentech has notified physicians of the first case of progressive multifocal leukoencephalopathy (PML) in a patient taking ocrelizumab (Ocrevus), MedPage Today has learned.

The case occurred in a JC virus-positive patient who had stopped taking natalizumab (Tysabri) in February after being on the drug for three years, and switched to ocrelizumab with a first dose given in April.

The patient was involved in a compassionate use program in Germany, according to a Genentech spokesperson.

It's unclear if the PML case stemmed from the natalizumab treatment -- the drug has long been known to increase the risk and was briefly taken off the market in consequence -- or whether the switch to ocrelizumab played a role. But the Genentech spokesperson said the treating physician ruled it as a carry-over from natalizumab.

âPatient safety is Genentech and Rocheâs highest priority and we are gathering more details about the case and the patientâs history,â the company said in a statement to MedPage Today. âWe will continue to share information with healthcare providers and global health authorities as we know more.â