Pfizer Inc. and Spark Therapeutics Inc. said their investigational drug SPK-9001 produced "dramatic reductions" in bleeding in 15 hemophilia B patients.
The patients are participants in a phase 1/2 clinical trial of SPK-9001 for severe or moderately severe hemophilia B.
According to study results as of May 7, all 15 patients showed a 98% reduction in annualized bleeding rate, the number of bleeding events divided by a certain length of time, with a 99% reduction in annualized infusion rate. An infusion therapy refers to a drug administered intravenously or through a non-oral route.
All participants have discontinued prophylactic clotting factor infusions. None of them experienced serious side effects. There were no thrombotic events — blood clots inside a blood vessel — or factor IX inhibitors, substances that suppress the activity of clotting factor IX.
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Two patients, one of whom received SPK-9001 manufactured using an enhanced process, reported related side effects of elevated transaminases, a type of enzyme, and were treated with a tapering course of oral corticosteroids, anti-inflammatory medicines that treat allergic reactions. The patients experienced no symptoms, and one of the adverse events was resolved.
One additional participant received oral corticosteroids, with gradual reduction of dosage over time, for an increase in liver enzymes temporally linked to falling levels of factor IX activity.
Philadelphia-based Spark expects to complete the transition of a hemophilia program, called SPK-FIX, to New York-based Pfizer in the summer, and anticipates delivering a batch of drug substance to Pfizer, allowing the drugmaker to launch a phase 3 clinical trial of SPK-9001.

