Natalizumab (Tysabri) appears to be a highly effective disease-modifying treatment for PwMS. Given by monthly infusion, it has been shown in clinical trials to markedly reduce relapse rate.
However, because of the risk of the often fatal nervous system infection, progressive multifocal leukoencephalopathy (PML), a risk that grows with continuing use of the drug, it is considered a second line therapy when others don't appear to be effective, and is not thought to be suitable as a lifelong medication.
It has been known however, that stopping the drug can result in a return to the level of disease activity that was present when the drug was started. Some have even shown a rebound effect on stopping Tysabri, where disease activity is increased to a level above that present when starting the drug.
Italian researchers have now examined clinical and radiological data from 54 patients beginning two years before starting Tysabri, data while on treatment, and data for a year after stopping Tysabri.
Their results confirm the concerns about disease reactivation after stopping the drug. This group of PwMS had particularly active disease, that presumably being the reason they were started on this drug. Their relapse rate as a group was around 1.7 relapses a year prior to starting Tysabri. The drug appeared highly effective in controlling this disease activity, with the relapse rate falling for the group to around 0.2 per year while on the drug, staying at this level for the first three months after stopping the drug. But then, the disease activity increased markedly for the group, climbing to a relapse rate of around one per year. This was still below the pre-treatment level of around 1.7 per year, but represented a very marked reactivation of the disease process.
Importantly, treatment with any of the immune modifying therapies after stopping Tysabri did not prevent this increase in disease activity, except re-starting Tysabri, which was effective. However, this is clearly not a feasible option as for many PwMS, the drug was being stopped because of the risk of staying on it for too long.
So while Tysabri appears a very effective therapy for those with very active disease, careful consideration needs to be given before starting treatment to these issues around stopping the drug.