Tysabri (natalizumab)


Tysabri (natalizumab) is an injectable disease-modifying treatment, delivered by intravenous infusion every four weeks, approved by the FDA for the treatment of relapsing forms of MS to delay progression of disability and reduce frequency of exacerbations and is produced by Biogen Idec and Elan Pharmaceuticals. Tysabri is generally recommended for use in people who have had an inadequate response to, or who have not tolerated, other disease-modifying treatments.


How does Tysabri work?

Tysabri is a humanized monoclonal antibody that serves as a receptor antagonist against the alpha 4 integrin cell adhesion molecule present on the surface of all leukocytes (a type of white blood cell that plays an important role in the immune system). Tysabri attaches to alpha 4 integrin and, by doing so, inhibits the leukocyte from carrying out its function as a part of the immune response. Although we don’t understand exactly how Tysabri works to reduce exacerbations and slow progression of disability in MS, by inhibiting the function of leukocytes, it appears to interfere with the abnormal immune response thought to be involved in MS.


How is Tysabri taken?

Tysabri is taken as an intravenous (IV) infusion given over 1 hour every 4 weeks. The recommended dose of Tysabri is 300 mg. Tysabri is only available in the US through doctors who are enrolled in the TOUCH Prescribing Program (TYSABRI Outreach: Unified Commitment to Health). The TOUCH Program ensures that Tysabri is prescribed and infused in a safe manner.


What evidence do we have that Tysabri works?

Tysabri was tested in people with MS in two randomized, double-blind, placebo-controlled studies. The studies included people with MS who had had at least 1 exacerbation during the year before the study and a certain level of disability as measured by the Kurtzke Expanded Disability Status Scale (EDSS).

Participants in Study 1 were randomly assigned to receive Tysabri 300 mg (n=627) or placebo (n=315) every four weeks for up to 28 months (30 infusions). Study 2 included people who had had 1 or more exacerbations while taking Avonex (interferon beta-1a) during the year before the study. Participants in Study 2 continued to receive Avonex weekly and were randomly assigned to receive Tysabri (n=589) or placebo (n=582) every four weeks for 28 months.

In both studies, the groups that received Tysabri (in Study 1, Tysabri alone, and in Study 2, Tysabri + Avonex) had significantly longer periods of time to sustained increase in disability and fewer exacerbations compared with the placebo groups (in Study 1, placebo alone, and in Study 2, Avonex + placebo).


Is there a generic form of Tysabri?

A generic form of Tysabri is not available.