The federal judge overseeing the patent battle between Amgen and Roche has ordered that an expert be appointed to recommend how to compare the dosing and prices of their anemia drugs, Reuters reports.

Last October, a federal court jury in Boston found that patents on Amgen’s anemia drugs were valid and that Roche’s Mircera, which has since been approved by the FDA for treating anemia in kidney disease patients, infringed three patents. But US District Court Judge William Young declined to issue a permanent injunction barring Mircera sales in the US and may instead impose a licensing deal allowing Roche to launch its drug - which is administered less often than Amgen’s Epogen and Aranesp - if certain terms are met.

Roche offered to pay a 22.5 percent royalty to Amgen and agreed not to charge more than rivals. Amgen, however, rebuffed the offer. Even though Amgen prevailed in the patent case, a compulsory license is now a possibility, following a 2006 US Supreme Court decision in eBay vs. MercExchange, which weakened the powers of courts to issue injunctions barring firms from using infringing technology, Reuters writes. Judge Young has said it may not be in the public interest to ban Mircera.

UPDATE: Meanwhile, Amgen has now filed a motion asking the judge to allow for a trial to determine compensation if Roche is allowed to sell Mircera in the US, unless Young issues a permanent injunctdion. Amgen would withdraw its motion if an injunction is granted. This is the motion.

In an order filed today, Young wrote he “continues to grapple with complex issues related to Amgen’s request” for a permanent injunction and ordered the appointment of a “special master” to make recommended findings regarding price parity, as well as the dose conversion ratios for Mircera and Epogen. He gave Amgen and Roche 15 days to submit a list of candidates and the expert will have 60 days after that to make the requested findings.

An Amgen spokesman writes us to say: “Amgen believes a permanent injunction is the appropriate remedy in this case. We will recommend candidates as the court has requested and look forward to providing facts on pricing and dose conversion to the appointed Special Master.”

Last week, a federal appeals court ruled that Roche’s Mircera anemia med could be imported - so long as it wasn’t for sale, but reversed a decision from the International Trade Commission that it couldn’t rule on whether the importation infringed on patents held by Amgen.