The decision clears the way for a generic copy of the drug produced by rival firm Actavis.
The ruling compounds the big fall in sales looming for AstraZeneca due to patents expiring on various drugs and medicines.
This expected slump prompted a $2.3bn (£1.5bn) restructuring plan and further job losses announced by chief exec Pascal Soriot last month.
AstraZeneca said yesterday it strongly disagreed with the court’s decision and was considering next steps, including lodging an appeal.
The District Court for the District of New Jersey ruled in favour of Actavis, which has developed a generic version that it now intends to launch immediately.
The verdict will not change AstraZeneca’s revenue guidance for 2013, which is that the company anticipates a mid to high-single digit decline in sales.
But Britain’s second-biggest drugmaker said additional generics entering the US market would materially impact royalties received on sales of Teva’s existing generic version of Pulmicort Repsules.
Analysts at Panmure Gordon yesterday cut their 2013 adjusted earnings forecasts by 3.7 per cent, describing the lower court ruling as a blow.
Total branded and generic sales of Pulmicort Repsules were around $1.2bn in the United States in the 12 months to January, Actavis believes.