Progressive Multifocal Leukoencephalopathy

Progressive Multifocal Leukoencephalopathy (PML) is a rare, generally fatal brain disease which is caused by the common JC virus.

Three cases of PML were reported in clinical trials of Tysabri. There were two deaths: one in a person with MS was also taking Avonex, and one in a person with Crohn’s disease who was also taking immunosuppressants. Since Tysabri was introduced in to the market in 2006, 95 cases of PML and 20 deaths have been reported. New data suggests that the risk of developing PML increases with longer treatment duration however the risk for people taking Tysabri beyond 3 years is yet to be determined. The risk of PML also increases in people who have been treated with an immunosuppressant prior to receiving Tysabri.

Although the initial cases of PML that occurred in the clinical trials were in participants who were also taking another disease-modifying medication, additional cases of PML in people who were not taking another disease-modifying medication at the same time have been reported in the post-marketing phase.

Tysabri has been found to increase the risk of liver damage, even after a single dose. Anyone experiencing symptoms of liver injury, including yellowing of the skin and eyes (jaundice), unusual darkening of the urine, nausea, feeling tired or weak, and vomiting, should contact his or her physician immediately. Blood tests can be done to check for liver damage.

Tysabri is not recommended for use by anyone whose immune system is weakened by disease or by the use of medications that alter the immune system, including other disease-modifying therapies. Currently, nothing is known about the safety of long-term use of Tysabri or whether additional side effects will emerge in time. People using Tysabri should promptly report any continuously worsening symptoms to their prescriber.

The absolute risk for PML in people treated with Tysabri cannot be precisely estimated and there are no interventions that are known to cure PML once it occurs, but a course of plasma exchange to remove Tysabri from the bloodstream as quickly as possible may provide benefit.

A large-scale study (TYGRIS) is currently investigating the risk of PML in people receiving natalizummab monotherapy for several years. The drug’s manufacturers recommend that people who take Tysabri enroll in the Canadian Tysabri Care Program at 1-888-827-2827.