Tysabri® (natalizumab)

Parent companies: Biogen Idec and Elan Pharmaceuticals, Inc.

• Administered via intravenous infusion every four weeks. Dose is 300 mg. Approved for individuals with relapsing types of MS. This drug is generally recommended for patients who have not responded adequately, or who cannot tolerate, another treatment for MS.


• Tysabri has been shown to reduce the number of relapses and slow disease progression. It also reduces the number of lesions in the brain as seen on repeated MRI scans.


• This laboratory-produced monoclonal antibody acts against a molecule involved in the activation and function of lymphocytes and their migration into the central nervous system (CNS). Recent data suggest that it may also enhance myelination and stabilize damage to the myelin sheath. Preliminary results suggest that the drug may actually produce an improvement in function.


• Recent studies indicate that the drug increases the cumulative probability of achieving a sustained improvement in disability in RRMS, and substantially reduced clinical and MRI activity after breakthrough disease on other therapies.


• Following a suspension of the drug after two patients developed Progressive Multifocal Leukoencephalopathy (PML), an often-fatal viral infection of the brain, Tysabri was re-released. All patients now receive the drug through safety monitoring programs such as the Tysabri Outreach: Unified Commitment to Health (TOUCH™) Prescribing Program and registered infusion centers and pharmacies; and the international Tysabri Global ObseRvation Program In Safety (TYGRIS). Approximately 56,700 patients have been treated with the drug worldwide, with about 35,000 currently taking it; there have been 10 reported cases of PML since the re-release, in addition to the two cases seen in the early trials. Studies are ongoing to see if it is possible to predict which individuals may be at risk for this condition.


• Some side effects include liver damage, a three-fold increased incidence of herpes zoster infections, occasional infections of a variety of types, and rare instances of anemia that are easily treatable.


• The drug shows continued effectiveness, as measured by a reduction in relapses, favorable MRI data, and a reduction in progression of disability. It also shows promise as a therapy in patients who had a previously poor response to other disease-management agents. It significantly improves patients' perception of health-related quality of life, reduces MS-associated pain, has at least a mild positive effect on fatigue and depression, improves fatigue and cognitive function, and may reduce loss of vision associated with RRMS.