Kreipke says that previous drugs to target blood vessel constriction have caused the vessels to dilate too much, which can put a patient at risk of bleeding. Clazosentan, he says, has a more specific action—it blocks a receptor in cells called endothelin receptor A, which is involved in vessel constriction. “This drug doesn’t cause more blood flow,” he says—it just decreases the severity of the drop in flow.

Ross Zafonte, a TBI expert at Spauding Rehabilitation Hospital in Boston, says the concept of targeting blood flow abnormalities in TBI is promising, and adds that this drug, with its specific molecular target, is a “more refined and elegant variant” on this strategy. But he cautions that many TBI treatments developed over the years “have looked good in the laboratory,” including in rodent tests, “yet very few things have been shown to be helpful in humans.”

Clazosentan, which is manufactured by Swiss company Actelion Pharmaceuticals, has recently been investigated as a treatment for brain hemorrhage, but clinical trial results have been disappointing. Kreipke has higher hopes for its efficacy in TBI. Because the drug has already been through safety testing in humans, he hopes to move ahead soon with a clinical trial for patients with moderate to severe TBI.