according to Biogen: “Accumulating experience indicates that the risk of PML increases with longer treatment duration. In addition, patients treated with an immunosuppressant (IS) prior to receiving TYSABRI have an increased risk of PML; IS use includes agents such as mitoxantrone, azathioprine, methotrexate,cyclophosphamide, mycophenolate and cladribine. This increased risk appears to be independent of TYSABRI treatment duration and is based on the fact that 46% of TYSABRI patients with PML had been treated with an IS prior to receiving TYSABRI. From the TYGRIS Observational Study, it is estimated that 20% of TYSABRI-treated patients (13% in US and 24% in EU) have been treated with an IS prior to receiving TYSABRI. Hence, there appears to be a disproportionate representation of prior IS use in the patients with PML compared to the TYSABRI-treated population overall,
The data indicate that patients with prior IS use have ~4-fold greater risk of PML compared with patients without prior IS use.
Patients with prior IS use have ~2-3 fold greater risk of PML compared with the overall TYSABRI-treated population, and patients without prior IS use have ~50% lower risk of PML compared with the overall TYSABRI-treated population. The US TYSABRI prescribing information now reflects these observations. Nevertheless, the overall worldwide incidence of PML associated with TYSABRI therapy since reintroduction remains generally consistent with the rate previously observed in clinical trials (1). Databeyond 3 years are limited.”