Circassia Pharmaceuticals Plc is a holding company, which engages in the development and commercialization of respiratory products. It operates through the NIOX, and US AZ Collaboration segments. The NIOX segment includes a portfolio of products used to improve asthma diagnosis and management by measuring fractional exhaled nitric oxide. The US AZ Collaboration segment relates to the U.S. collaboration agreement with AstraZeneca regarding the commercialization of Tudorza and Duaklir brands. The company was founded by Steven Harris and Charles Stuart Webb Swingland on May 19, 2006 and is headquartered in Oxford, the United Kingdom.