The court ruled in favor of three generic drug manufacturers, Andrx Corporation, KV Pharmaceutical, and Eon Labs, the generics subsidiary of Novartis AG.
All three manufacturers are now said to be preparing their own copycat versions of the drug, although it could still take sometime before the generic versions win approval from the FDA.
The patents protecting the drug were due to expire in September 2007, and analysts quoted in the Times Online had projected total revenues from the drug up until that date to be in the region of $2.3 billion.
Shares in AstraZeneca dropped by almost 5% after the surprise court ruling.