A U.S. judge handed AstraZeneca Plc a huge victory Tuesday, finding that the patent on its multibillion-dollar cholesterol fighter Crestor is valid, sending the the British drugmaker’s shares up 9 percent.

Judge Joseph Farnan, of the U.S. District Court in Delaware, ruled that generic drugmakers who challenged the patent failed to prove it was invalid because it was an obvious invention.
Farnan further ruled that privately held Canada-based generic drugmaker Apotex may be held liable for infringing the patent on AstraZeneca’s biggest product, known chemically as rosuvastatin.

While industry observers widely believed AstraZeneca was likely to win the case, billions of dollars were at stake since more than 80 percent of a branded drug’s sales evaporate when faced with generic competition.

Crestor, which belongs to the world’s most widely used class of medicines called statins, had sales of $4.5 billion in 2009 and is forecast to reach $6.5 billion in 2013, according to estimates compiled by Thomson Reuters.

“Judgment will be entered in favor of plaintiffs and against defendants on the issues of invalidity and unenforceability of the 314 patent,” Farnan wrote in his 44-page ruling.

AstraZeneca shares traded on the New York Stock Exchange closed up $4.02, or 9 percent, at $48.74.