BOSTON (Reuters) - Two more patients taking Biogen Idec Inc’s multiple sclerosis drug Tysabri have developed a potentially deadly brain infection known as PML, the company said on Wednesday.
The Cambridge, Massachusetts-based biotechnology company said in its latest monthly update that as of October 1, there have been 70 confirmed cases of PML, up from 68 as of September 2.
Of those, 14 have died and 56 are alive with varying degrees of disability ranging from mild to severe. There were no additional deaths in October.
Tysabri, which Biogen sells in partnership with Irish drugmaker Elan Corp Plc, is an important growth driver for both companies, and is battling for share of an increasingly competitive market.
U.S. regulators recently approved the first oral MS drug, Gilenya, made by Novartis AG, which, while not as effective as Tysabri, is more convenient, since Tysabri must be infused roughly once a month.
Genzyme Corp, which recently reported five-year follow-up data from its experimental MS drug Campath, shows even greater efficacy than Tysabri but also carries worrisome side effects.
Tysabri was temporarily withdrawn from the market in 2005 after it was linked with PML, but reintroduced in 2006 with stricter safety warnings. Since its reintroduction, the overall incidence of PML, based on the 70 cases, is estimated to be 0.91 per 1,000 patients, up from 0.90 in September.
As of June 30, about 71,400 patients had received Tysabri since it was launched.
Biogen is developing a test that it hopes will be able to identify patients at higher risk for developing PML. In the meantime, the risk has been shown to increase with duration of therapy.
For patients who received more than 24 infusions of the drug, the rate of PML was 1.87 per 1,000 patients in October, up from 1.86 in September. The rate for patients receiving between 13 and 24 infusions was 0.38 per 1000, down from 0.39 in September. For patients who received between 25 and 36 infusions, the rate was 1.44 per 1,000, down from 1.46 in September.
Reporting by Toni Clarke; Editing by Gary Hill