The Search for Safer Blood Thinners

Drug companies are developing treatments with less risk of causing unintended bleeding

- Rebecca Penty and David Rocks

Blood clots are estimated to cause about one in four deaths worldwide, and the leading blood thinners prescribed to prevent them are among the most widely used medicines. Known under the brands Eliquis and Xarelto, the drugs are called Factor Xa inhibitors after the enzyme they block in the body's natural clotting process. In rare cases, however, switching off Factor Xa can cause unintended consequences, ranging from bruising easily to life-threatening internal bleeding, limiting who can take the medicines. Now drugmakers are working on alternatives that act on a different enzyme to dramatically reduce those risks.

If the emerging treatments are proven safe and effective, they'll allow pharmaceutical companies to target the roughly eight applications where Eliquis and Xarelto can't be used, including, critically, preventing strokes in people who've already had one, says Andrew Baum, an analyst at Citigroup Inc. It will take a few more years before any of them become available: Three of the experimental drugs that have generated buzz-from Bayer, Bristol-Myers Squibb and its partner Johnson & Johnson, and Novartis spinout Anthos Therapeutics-are in late-stage trials. And none would have meaningful sales until around 2028, after Eliquis and Xarelto are set to lose patent protection, Baum says. But the longterm potential is huge. He estimates the new drugs could become a $55 billion category by around 2035.