Novartis reports patient taking Gilenya developed rare brain disease

Expectations for the blockbuster status of Gilenya dimmed today when developer Novartis ($NVS) disclosed that a patient taking the multiple-sclerosis drug has developed a rare brain disease.

The company points out that the patient had previously been treated with Tysabri, a multiple-sclerosis treatment from Biogen Idec ($BIIB) and Elan ($ELN), which has already been tied to the sometimes-fatal brain disease known as PML, Dow Jones reports. The Swiss company acknowledged however, that that did not rule out the possibility that Gilenya may have contributed to the onset of progressive multifocal leukoencephalopathy.

The possible side effects of the only oral treatment for MS are being closely followed after a patient in the U.S. died in the fall within 24 hours of starting treatment. There have also been reports of heart issues associated with taking the drug.

Analysts suggested that the drug could be a big boost to Novartis as it sees revenue from its heart drug and top-seller Diovan get depleted as its patent is shed. There are already 25,000 patients taking the medication, and estimates are that Gilenya sales could top $1 billion a year.

The FDA has been doing a review of the drug in the face of reports of 11 deaths in the U.S. associated with it. The European Medicines Agency, which regulates drugs in the EU, in January began a review of Gilenya's benefits and risks. It is slated to make a ruling on its findings April 20.

- check out the Dow Jones story