A patent granted to Swiss giant Roche for a hepatitis C drug has been revoked by an Indian panel.
This move is the latest setback for global pharmaceutical firms in the country's $12-billion medicine market.
The Intellectual Property Appellate Board overturned the patent awarded by the Indian Patent Office to Hoffmann-La Roche's drug Pegasys used to treat hepatitis C -- a disease that can lead to fatal liver problems.
While Roche can still challenge the decision in the Indian courts, patients' advocacy groups called the ruling a significant victory.
"If we get the manufacture of lower-costing generic drugs, millions suffering from hepatitis C -- both in India and globally -- will benefit," said patients' rights lawyer Anand Grover.
"This is a big win for hepatitis C patients," he told AFP.
India is the world's leading exporter and manufacturer of cheap, non-branded medicines -- mainly to other developing countries.
The ruling represents another blow to western drug firms in India that have been looking to the country of 1.2 billion people to boost sales but are worried about the country's patent protection.
Earlier this year, the same board allowed a local firm to produce a vastly cheaper copy of Bayer's patented drug Nexavar for liver and kidney cancer, saying the $5,300 price charged by the German company was "exorbitant".
The decisions involve interpretation of stricter drug patent protection rules introduced by India in 2005 to comply with World Trade Organization regulations.
The patent appeal board ruled on Friday there was nothing new in the development of Pegasys.
"In the end, the invention is held to be obvious," the board said, declaring the patent "set aside".
The ruling was in response to an appeal against the patent filed by a Mumbai non-profit group, The Sankal Rehabilitation Trust, which helps drug users who frequently contract hepatitis C through use of dirty needles.
Hepatitis C -- a viral disease transmitted largely through infected blood that can lead to liver cirrhosis and cancer -- represents a huge public health problem in India and globally.
Some 10 million to 12 million Indians, including 50 percent of injecting drug users, are infected with the virus, but many receive no treatment because of the high cost, according to the Sankal trust.