Background Natalizumab (NAT) is a recombinant humanised anti-α4-integrin antibody used in treating Relapsing Remitting (RR) Multiple Sclerosis (MS).

Purpose To evaluate the long-term safety and efficacy of NAT in Cypriot patients, to assess the frequency of anti-JC Virus (JCV) antibodies and implement a strategy for the prevention of PML.

Materials and Methods Twenty-two patients were studied prospectively for 3 years.

The patients received 300 mg of NAT intravenously every 4 weeks. MRI examinations were performed at study entry and 12–24 months after the start of treatment. JCV antibody testing was performed after two years of treatment.

Results Six patients (27.3%) discontinued the study due to: Severe allergic reaction (9%), generalised atony, fatigue and weakness (4%), recurring herpes infection (4%), family planning (4%) and presence of anti-JCV antibodies (anti-JCV positive) due to previous immunosuppressive therapy (4%).

Most frequently reported side effects were: cardiovascular (41%), general (41%), laboratory abnormalities (41%), gastrointestinal (23%), neurological (18%), allergic reactions (18%) and depression (14%).

After three years of NAT treatment, a 55.2% decrease from the baseline mean annual relapse rate was observed, as well as improvement of 0.3 points on the mean Expanded Disability Status Scale (EDSS) Score.

87.5% of the patients completing the study had repeat MRI scans. Of those, 85.7% were found to have no new or gadolinium-enhancing lesions.

JC Virus antibody testing was performed after two years of NAT. Of the thirteen samples, eight (61.5%) tested positive. Two of those (25%) discontinued NAT due to previous IV mitoxantrone treatment. The remaining patients continued treatment under close supervision by the attending neurologist.

No cases of Progressive Multifocal Leukoencephalopathy were reported.

Conclusions Long-term therapy with natalizumab proved to be safe and effective in our population. Strict follow-up criteria were implemented for JCV antibody-positive patients remaining on treatment with natalizumab for more than two years.

No conflict of interest.