In a Complete Response Letter (CRL) to Biogen, the U.S. FDA said it is unable to approve the company's supplemental Biologic License Application (sBLA) for a subcutaneously delivered form of Tysabri, a drug used in the treatment of relapsing multiple sclerosis.
According to Biogen, the CRL indicates that the FDA is unable to approve the filing in its present form; the drugmaker is evaluating the agency's response and will determine next steps in the U.S. The drugmaker did not reveal why the sBLA was rejected and has turned down media requests for further explanation.
An intravenous formulation of Tysabri was approved by the FDA in 2004. The new formulation is a subcutaneous injection. The injections are dosed at 300 mg every four weeks by a health care provider, with the goal of treating patients in a clinical setting beyond infusion centers.
The subcutaneous delivery of Tysabri was approved by the European Commission in March 2021 after regulators ruled the drug had comparable efficacy and safety to the intravenous formulation with reduced administration time.
Biogen plans to pursue regulatory filings of the new formulation in additional countries.
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