Cara Therapeutics' (NASDAQ: CARA) stock has been on a tear following news that Vifor Fresenius Medical Care Renal Pharma Ltd. licensed certain ex-U.S. rights to Korsuva, Cara Therapeutics' treatment for chronic kidney disease-associated itching in dialysis patients. Since the news was reported, Cara Therapeutics shares have risen from less than $12 per share to over $17 per share, including a gain of as much as 12.5% on Friday.Korsuva is a kappa opioid receptor agonist that relieves pain by targeting nerves in sensory nerves.