SAN FRANCISCO — New York drugmaker Acorda Therapeutics Inc. has tapped Paul Hastings to take on a hedge fund that’s declared war on pharmaceutical patents.

J. Kyle Bass and Dallas-based Hayman Capital Management say that drug firms are using expired or otherwise invalid patents to maintain monopoly pricing of their medicines. Partnering with Erich Spangenberg and patent monetization firm IP Navigation Group LLC, Hayman Capital brought two petitions for inter partes review last month under the name Coalition for Affordable Drugs. Each targeted Acorda Therapeutics and its multiple sclerosis treatment Ampyra.