Merck & Co is buying clinical-stage biotech Afferent Pharmaceuticals in a deal worth up to $1.25 billion.

Under the deal, the firm will purchase all outstanding shares of Afferent for an upfront fee of $500 million, and could pay an extra $750 million linked to certain clinical development and commercial milestones.

The moves gives Merck access to Afferent's lead investigational candidate AF-219, a selective, non-narcotic, orally-administered P2X3 antagonist currently being evaluated in a Phase IIb clinical trial for the treatment of refractory, chronic cough, as well as in a Phase II clinical trial in idiopathic pulmonary fibrosis (IPF) with cough.

P2X3 receptors are believed to play a key role in the sensitisation of certain sensory nerves, which become activated under pathological conditions mediated by a common cellular signal, ATP, when it is released in high concentrations due to cellular distress following injury or infection. Afferent's compounds are designed to selectively block ATP activation of P2X3 channels, potentially reducing a range of sensory signs and symptoms.

The prevalence of chronic cough (a cough lasting more than eight weeks) is estimated to be around 10 percent of adults in the US; in up to 40 percent of cases no underlying condition can be identified and thus these patients are typically not responsive to symptomatic treatment. There are currently no approved therapies for the condition.

"Afferent has pioneered the clinical development of novel investigational candidates selectively targeting the P2X3 receptor, an exciting area of research," said Merck Research Laboratories president Roger Perlmutter. "We look forward to advancing these innovative molecules for patients with conditions like chronic cough, an area of significant unmet medical need."

The transaction is expected to close in the third quarter of this year.

FDA panel backs C diff antitoxin
Meanwhile, a US Food and Drug Administration advisory panel has backed approval of Merck's Zinplava (bezlotoxumab), an investigational agent for prevention of Clostridium difficile infection recurrence.

The Antimicrobial Drugs Advisory Committee agreed, with a vote of 10 to five with one abstention, that Merck has provided substantial evidence of the safety and effectiveness in its proposed indication.