New blood thinners will prevent blood clots without causing bleeding

livemint.com:

A new class of anticoagulant drugs on the horizon is taking fresh aim at one of cardiology’s toughest challenges: how to prevent blood clots that cause heart attacks and strokes, without leaving patients at risk of bleeding. At least a half-dozen experimental blood thinners are in development that inhibit a protein called factor XI, one of several blood factors that regulate how the body forms clots. The challenge is this: The body generates two types of clots—good ones that plug holes in blood vessels to stop bleeding caused by external injuries, and bad ones that grow inside arteries and veins.

These can block blood flow to critical organs, potentially leading to injury or death. For decades, drugs developed to prevent the bad clots have targeted proteins involved in forming both types of clots. As a result, preventing clots often comes at the price of a higher risk of bleeding, causing many patients to refuse to take, or stop taking, the medicine.

“Too low of a dose, you clot; too high of a dose, you bleed," says Dr. Michael Gibson, cardiologist and CEO at the nonprofit Baim Institute for Clinical Research at Harvard Medical School. “Our goal is to keep people from falling off the balance beam.

This is what we have been chasing for years." Factor XI, it turns out, is crucial for the formation of the bad clots inside blood vessels, what doctors call thrombosis. But researchers now believe that factor XI, unlike other blood factors, plays a minimal role in forming the good clots that stop bleeding. That suggests drugs against it could prevent the bad clots without significantly disrupting the process that causes good clots, and thus minimize excess bleeding associated with anticoagulants and other blood thinners.