AstraZeneca has filed a lawsuit in the Delhi High Court against Indian drug maker Dr Reddy’s Laboratories to block it from launching generic versions of Brilinta, its blockbuster medicine for heart ailments.

The UK biopharmaceutical company claims potential launch of copies infringes its existing patent on the drug. Court asked Dr Reddy’s on Tuesday to file a reply to the lawsuit and will hear its arguments on July 31, said lawyers aware of developments. Until then, Dr Reddy’s cannot launch its generic version of the drug, they told ET.

Copies of the drug can be manufactured only after all the patents covering it expire, AstraZeneca’s counsel argued in court on Tuesday.

Brilinta, used to reduce chances of heart attacks or strokes by preventing blood clots in vessels, achieved blockbuster status in 2017 when it raked in over $1billion in global sales for AstraZeneca. Dr Reddy’s generic version was to be marketed as Ticaflo, according to people aware of the development. Dr Reddy’s has not been seen as an aggressivechallenger of drug patents in India

One of AstraZeneca’s key patents for Brilinta expired in India earlier this month, triggering launch opportunities for local drug makers, said people familiar with the development. However, AstraZeneca argued that one patent is still valid and effectively bars commercial launches of copies.