Stronger Label for BIIB's Tysabri - Analyst Blog

The US Food and Drug Administration (FDA) recently issued a notice on its website regarding the risk of developing progressive multifocal leukoencephalopathy (PML) with increased use of Tysabri. Tysabri, which is marketed by Biogen Idec (BIIB) and Elan Corp. (ELN), is approved in the U.S. for the treatment of relapsing forms of multiple sclerosis (MS) and moderately to severely active Crohn's disease.

The decision to update the safety information on Tysabri’s label is based on reports of 31 confirmed cases of PML, a rare but serious brain infection. The agency’s move comes a couple of weeks after the European Medicines Agency (EMEA) Committee for Medicinal Products for Human Use (CHMP) arrived at the conclusion that the risk of a patient developing PML increases after having taken the drug for two years or more, though the risk remains low. However, like the FDA, the CHMP maintained that the benefits of the drug outweigh its risks.

Tysabri is administered as a single intravenous infusion every four weeks. It has been observed that the overall worldwide cumulative rate of PML in patients who have received one or more infusions is 0.5 cases per 1,000 patients. This rate increases with the number of infusions received.
 
Until now, no cases of PML have been reported in patients treated with Tysabri for less than 12 months. The overall worldwide cumulative rate of PML in patients who have received at least 24 infusions is 1.3 cases per 1,000 patients (0.8 per 1,000 patients in the US and 1.9 per 1,000 patients outside the US ).

The revised label will not only warn about the risk of developing PML with increased use of Tysabri, it will also contain information regarding the occurrence of Immune Reconstitution Inflammatory Syndrome (IRIS) in patients who developed PML and subsequently discontinued Tysabri. The Tysabri label already includes a black box warning regarding the occurrence of PML.

Tysabri was initially approved in 2004 but was withdrawn from the U.S. market in 2005 due to the PML concern. The drug was reintroduced after a year with a strict warning regarding the occurrence of PML. 

Despite the black box warning, Tysabri sales continue to grow. Biogen recently announced that Tysabri sales crossed $1 billion in 2009. However, we note that the number of new patients adopting Tysabri has been declining over the past few quarters. Additional instances of PML cases could hamper the product’s acceptance in the medical community, thereby limiting its sales growth.

We currently have a Neutral recommendation on Biogen.
 
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