How safe is natalizumab for long-term multiple sclerosis (MS) treatment?

Answer From Dean M. Wingerchuk, M.D.

Natalizumab (Tysabri) is a drug treatment for people with relapsing forms of MS. It's approved as a monotherapy, which means it's not to be taken in combination with any other disease-modifying drug. Studies show that natalizumab is associated with a reduced risk of disability progression, improved cognitive performance and fewer relapses.

However, natalizumab has also been associated with complications, most notably a rare but serious condition known as progressive multifocal leukoencephalopathy (PML). PML is a central nervous system disorder caused by infection with JC virus (JCV). This virus infects 60 to 80 percent of the world's population without consequences but can cause PML in people who have immunocompromised conditions.

Because natalizumab increases the risk of PML, your doctor should consider whether the expected benefits of taking it are sufficient to offset this risk. The main PML risk factors include:

  • Presence of anti-JCV antibodies
  • Prior use of immunosuppressant medications
  • Treatment with natalizumab for more than two years

Based on the risk factors, treatment recommendations have been proposed that include testing for JCV antibodies prior to starting treatment with natalizumab, every six months during treatment, and for at least six months after discontinuing treatment.

Other more commonly reported side effects of natalizumab are not as serious. They include fatigue, anxiety, sore throat, sinus congestion, swelling and allergic reactions.

Although it's not a common side effect, some people have developed serious liver injury after their first natalizumab treatment. These liver complications normally appeared after the first treatment and went away after discontinuing natalizumab therapy.


Dean M. Wingerchuk, M.D.

Feb. 17, 2018 See more Expert Answers