Merck & Co. has agreed to pay up to US$1.25 B to acquire Afferent Pharmaceuticals in return for the latter’s proprietary P2X3 receptor based assets. Afferent will receive US$500 M upfront in cash and an additional consideration of US$750 M that is linked to the attainment of certain clinical and commercial milestones of Afferent’s pipeline which includes AF-219, a selective small molecule and an orally-administered P2X3 antagonist, that is in Phase IIb trials for the treatment of refractory chronic cough.