Gilead Sciences Inc. has been ordered to pay Merck & Co. $2.54 billion in royalties in a patent lawsuit over Gilead’s blockbuster hepatitis C drugs Sovaldi and Harvoni.

A federal court jury in Delaware found Thursday Merck’s patent, originally issued to Idenix Pharmaceuticals, a company Merck bought in 2014, was valid and that Gilead “willfully” infringed on it. The lawsuit was filed by Idenix in 2013.

The decision was Merck’s second victory over Gilead. It won a $200 million verdict against Gilead in March in another patent infringement case involving the hepatitis C drugs, but that verdict was overturned.

Gilead, based in Forest City, California, said it would appeal.

Merck sought 9 percent royalties on Harvoni and Sovaldi going forward.

“The jury’s verdict upholds patent protections that are essential to the development of new medical treatments,” Merck said in a statement.

“The patent at issue in this case facilitated significant advances in the treatment of patients with [hepatitis C] infection and was appropriately granted. Achieving these advancements required many years of research and significant investment by our subsidiary and its partners.”

Harvoni, which combines Sovaldi’s active ingredient with another drug, and Solvadi cured hepatitis C in 90 percent of patients but at a price. Harvoni lists for $1,125 per pill. A 12-week regimen runs $94,500. In 2015, Gilead made $20 billion from the two drugs.

The decision sent Gilead stock down 1.8 percent in after hours trading.

The decision came as Express Scripts added Harvoni to its 2017 national formulary but did not say whether it would be covered. Negotiations are still underway between Express Scripts and Gilead.

Some 25 million people suffer from hepatitis C, a liver infection that can result in chronic disease. The virus is spread by contact with contaminated blood. Most people have no symptoms, and those who do suffer fatigue, nausea, loss of appetite and yellowing of the eyes and skin.