This study is to find out the safety and effectiveness of Avonex (interferon-beta-1a) Therapy in patients who have developed neutralizing antibodies during previous interferon-beta treatment

This is a multi-centre, prospective, open label, non-comparative phase IV trial. Eligible patients will receive treatment with IFN-beta-1a AVONEX® 30 mcg i.m. once weekly for 12 months.The patients will be examined clinically and NAb titres will be performed at screening and after 12 months. Adverse event source verification will be performed during the documentation period.

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