* 95 PML cases, 20 deaths reported since 2007 relaunch
* Estimated incidence of PML per 1,000 patients now 1.16
NEW YORK, Feb 18 (Reuters) - Ten more patients taking Biogen Idec’s (BIIB.O) multiple sclerosis drug Tysabri developed the serious brain infection known as PML last month and there were reports of four more deaths, according to a monthly update by the U.S. biotechnology company.
The new cases of potentially fatal progressive multifocal leukoencephalopathy, or PML, were detected between Jan. 7 and Feb. 2, bringing the total number of confirmed cases to 95 and deaths to 20 since the drug was reintroduced into the market in July of 2007, Biogen said.
Biogen, which markets the drug with Ireland-based partner Elan Corp Plc ELN.I, said the overall rate of PML cases per 1,000 patients has edged slightly higher to 1.16. In November it had been 1.0.
The number of new PML cases per month has been climbing. Four new cases were reported in November and six in December.
“We know, and have known for some time, that PML increases with duration of time you are on therapy,” Biogen spokeswoman Naomi Aoki said. “As we see patients on therapy longer, it’s not surprising that you see new cases.”
Tysabri, considered the most important growth driver for Biogen and Elan, is given by infusion typically one a month.
For patients who have received between one and 12 Tysabri infusions the incidence of PML is just 0.01 per 1,000. That rises to 0.4/1,000 for between 13 and 25 infusions and to 1.64/1,000 for patients who have been on the drug between two and three years, the company said.
“Within these treatment intervals we’ve seen those numbers stay fairly steady,” Aoki said.
Tysabri was briefly pulled from the U.S. market over concerns about the brain infection.
But the drug was considered to be so effective compared with other available treatments that MS patients considered the risk worth taking and clamored for its return.
Health regulators relented and allowed a relaunch of the drug with certain restrictions, including close monitoring of patients and regular reporting of PML cases.
Reporting by Bill Berkrot; Editing by Richard Chang