Safety of Avonex Treatment in Multiple Sclerosis Patients With Neutralizing Antibodies to Interferon Beta Therapy

Inclusion Criteria: * Relapsing-remitting MS according to Poser criteria(CDMS or LSDMS)30 or MS according to McDonald criteria * Disability equivalent to an EDSS of 6.0 or less at screening * Neutralizing antibody titre \> 20 and \<500 in two consecutive NAb tests. One must be from before screening * previous treatment with either subcutaneous administered interferon-b-1b (Betaferon®) or interferon-b-1a (Rebif TM) prior to enrolment * A priori has been decided to be treated with AVONEX Exclusion Criteria: * Is NAb positive on AVONEX * History of major depression * Cardiac insufficiency, cardiomyopathy, significant cardiac dysrhythmia, unstable or advanced ischemic heart disease (NYHA III or IV), or significant hypertension (BP \> 180/110 mmHg) * Renal insufficiency defined as serum creatinine \> 1.5 times the upper normal reference limit * Any systemic disease that can influence the patient's safety and compliance, or the evaluation of the disability * Women who are pregnant, breast-feeding or have the possibility for pregnancy during the trial. To avoid pregnancy, women have to be postmenopausal, surgical sterile, sexually inactive or practice reliable contraceptives