A federal jury in California has ruled in favour of US drug maker Merck in a high-profile patent dispute with rival Gilead Sciences over sofosbuvir, the active ingredient in a new blockbuster hepatitis C treatment.

The unanimous ruling on Mar. 22 declared Merck’s patents were valid and came a month after a federal judge ruled that Gilead’s hepatitis C drugs Solvadi and Harvoni infringed Merck’s intellectual property.

Sofosbuvir is the active ingredient in Solvadi and Harvoni which were launched in 2013 and 2014, respectively, becoming blockbusters overnight.

The court fight started in 2013 when Merck staked a claim for 10% of Gilead’s earnings because sofosbuvir infringed two patents that cover related compounds. Gilead filed the lawsuit in 2013, seeking for Merck’s patents to be declared invalid.

Merck is now seeking more than $2 billion in damages as well as a 10% royalty on sales of the two drugs which generated more than $19 billion in global sales for Gilead last year, accounting for nearly two-thirds of its total 2015 revenue.

“The jury’s verdict accurately reflects the evidence in this case,” said Merck which won US approval in January this year for its own hepatitis C drug, Zepatier.

Gilead responded by saying it was disappointed by the verdict and that there were a number of remaining issues that had to be decided by the judge and jury. It is expected to appeal the ruling.

Merck had been a dominant manufacturer of hepatitis C treatments until Gilead’s drugs were approved. Those drugs, as well as Merck’s and new ones from rival firms, have transformed treatment for the liver disease.

The new therapies cure about 95% of patients in eight to 12 weeks compared with the older versions that required a year of treatment yet barely cured half of patients.