UPDATE 1-U.S. appeals court invalidates Acorda patents on MS drug

(Adds comment from Acorda)

Sept 10 (Reuters) - A U.S. appeals court on Monday invalidated Acorda Therapeutics Inc patents covering its multiple sclerosis drug Ampyra, opening the door to generic competition for the company's flagship product.

The U.S. Court of Appeals for the Federal Circuit affirmed a lower court ruling that four Acorda patents on Ampyra were invalid because they described obvious ideas.

Generic drugmaker Hikma Pharmaceuticals had challenged the validity of the patents.

Acorda's stock dropped more than 22 percent to $21.40 after the ruling.

Acorda Chief Executive Officer Ron Cohen said in a statement the company was disappointed by the decision and reviewing the possibility of a further appeal.

Cohen said Acorda had prepared for generic competition and, as a result, was well-capitalized and focused on the potential launch of Inbrija, its treatment for Parkinsons disease.

Analysts are forecasting $370 million in sales of Ampyra in 2018, according to Thomson Reuters data.

Hikma did not immediately respond to a request for comment. (Reporting by Jan Wolfe Editing by Bill Berkrot and Paul Simao)