The market is taking advantage of the exciting deal and $50m stake as the share price shoots 14% higher to 99.5p.
Circassia will acquire certain rights to chronic obstructive pulmonary disease (COPD) products Tudorza and Duaklir for $230m.
It also includes future sales-based royalties on commercialisation of Duaklir in US, which aims for approval from the Food and Drug Administration in 2019.
Circassia hopes the agreement will support its expansion into the US and attract future product acquisitions and in-licensing opportunities.
The company had a difficult time in 2016 after its main cat allergy treatment failed during clinical trials.
Following the disappointing results, management decided to transition from an allergy-focused biotech to a speciality pharmaceutical firm.
Cantor Fitzgerald analyst Brian White says: ‘Having suffered a significant setback with its lead immunotherapy programme last year, we see this as a positive step for Circassia as it seeks to exploit the commercial infrastructure it has in place in the US respiratory market.’
Tudorza is sold in 60 countries worldwide including the US, with AstraZeneca revenues from global sales reaching $170m with $80m generated in the US alone last year.
Duaklir is in Phase III development in the US for the treatment of COPD, although it has already been approved in the European Union and 50 other countries.