A patent protecting AstraZeneca’s (AZN) Pulmicort Respules asthma drug in the U.S. was deemed invalid on Tuesday, paving the way for a generic version of the drug to hit store shelves.

The company said on Tuesday a district court in New Jersey ruled in favor of generic drugmaker Actavis (ACT), which already developed a copy of Pulmicort Respules. Actavis, which is based in Parsippany, N.J., announced that it expects to launch its version of the drug immediately.

London-based AstraZeneca has recently seen its revenue decline, while fighting to keep patent protection for top selling drugs like cholesterol treatment Crestor. The company won a lawsuit over Actavis last month to hold off generic competition until 2016.

Also last month, the company said it plans to cut thousands of jobs as part of a $2.3 billion restructuring plan.

In an effort to keep its U.S. patent for Pulmicort Respules, AstraZeneca argued a new generic version would materially impact the royalties it receives on sales of a separate copy marketed by Teva Pharmaceutical Industries (TEVA), which has made its own version of the drug after striking a deal with AstraZeneca in 2008.

AstraZeneca made around $260 million in royalties last year, according to the company.

AstraZeneca said the ruling will not impact its broader 2013 revenue guidance, a percentage sales decline in the mid- to high-single digits.

According to Actavis, U.S. sales of Pulmicort Respules totaled $1.2 billion.

Shares of AstraZeneca were up 39 cents at $50.50 in pre-market trading Tuesday. Actavis shares closed Monday at $92.46 and were inactive in pre-market trading.

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