Real world data from over ten years of natalizumab use shows the drug continues to be effective in relapsing-remitting MS and without any new or unexpected safety signals.

The Tysabri Observational Program (TOP), which last reported after five years of data, has now reported on more than 6,000 patients from 17 countries including Australia.

Led by Professor Helmut Butzkueven, from Monash University and head of MS at the Alfred Hospital, the study found median exposure to the drug was 3.3 years but as long as 11.6 years.

Patients who came off the drug did so mostly due to a positive anti-JCV antibody serostatus (46.3%).

Lack of efficacy was rarely given as a reason for stopping the drug.

The study found early improvements in the annualised relapse rates (ARRs) on natalizumab were maintained long-term.

“During the 10 years of follow-up, the on-natalizumab ARR was 0.15 (95% CI 0.14 to 0.15), a 92.5% reduction from the ARR of 1.99 (95% CI 1.97 to 2.02) in the year prior to starting natalizumab,” the study said.

Improvements in ARR occurred regardless of age, baseline EDSS score, or the number of DMT’s prior to natalizumab initiation.

The cumulative probability of remaining relapse free at 10 years was 45.8%.

The study found 13.5% of patients experienced one or more serious adverse events but only 4.5% were thought to be related to the treatment.

The most common SAEs were infections and infestations, with an incidence of 4.1%; PML, pneumonia, urinary tract infection and herpes zoster were the most commonly reported infections.

“The results demonstrate excellent long-term safety and substantial disease control,” the study concluded.

“Long-term treatment was associated with a very low risk of non-PML opportunistic infection and cancer rates similar to those expected in the general population. The planned continued follow-up of TOP patients for up to 15 years will provide further data on real-world outcomes in natalizumab-treated patients.”