Extra patent protection for Enbrel could keep cheaper versions off the market until 2029. Credit: Bloomberg via Getty Images

Amgen has received another 17 years of patent protection on its blockbuster autoimmune drug Enbrel (etanercept)—which could mean that it will be on the market for 30 years before it faces competition from biosimilars. The patent (US8,063,182) came in November 2011 and was a surprise to many in industry; Merck, of Whitehouse Station, New Jersey, had already announced plans to develop and commercialize a biosimilar version of the drug, plans that are now likely to be shelved.

Enbrel is a recombinant human tumor necrosis factor (TNF)-alpha receptor fused to an IgG fragment that inhibits tumor necrosis factor signaling. Its approval in 1998 for the treatment of rheumatoid arthritis was followed by several other approvals for autoimmune diseases. With global projected sales of $7.8 billion in 2011, the drug is a key product for Amgen of Thousand Oaks, California, and Pfizer of New York, and the world's biggest-selling biologic.

Amgen was granted this unexpected stretch in patent protection because its '182 patent was filed in May 1995 under old rules that applied to patents filed before mid-1995. Those rules, which have now lapsed, awarded patents 17 years from the date of issue. This means the new patent will expire in November 2028. Current standards give patents 20 years from the date of filing.

The 16-year delay between the filing of the '182 patent and its issuance is probably due to a combination of a heavy workload and the backlog at the Alexandria, Virginia–based US Patent and Trademark Office (USPTO). According to Leslie Meyer-Leon, a patent attorney at IP Legal Strategies Group in Boston, who specializes in biotech patents, Amgen itself is unlikely to be culpable for the delay. “I don't think Amgen acted in a way that unfairly manipulated the system; if anyone is at fault in having this patent issued so late, it is the USPTO. Because of inadequate funding, they have a huge backlog of pending applications, especially for those applications whose initial rejection is appealed [which happened with the '182 patent] and so it can take a very long time for a patent to issue.” Meyer-Leon notes that the slow pace of patent prosecution can still occur under the current system.

Another change in US patent legislation has played in Amgen's favor. In 2000, the USPTO began to make pending patent applications publically available, and Amgen's filing preceded this. “The issuance of this patent has shock value “because the application was filed at a time when applications were not published and the prosecution records are not available online; thus, there is a surprise factor....” says Meyer-Leon. Some commentators believe it is unlikely there are many patents still pending entitled to a 17-year term from issuance (Nat. Rev. Drug Disc. 11, 9, 2012).

It had been anticipated that Enbrel would be subjected to generic competition soon after another key patent protecting Enbrel (US5,610,279) expired in October of this year. Indeed, in June 2011 Merck struck a deal worth up to $720 million with the Seoul, South Korea, company Hanwha Chemical to develop and commercialize HD203, a biosimilar version of Enbrel, in phase 3 trials that aim to show safety and equivalence in patients with rheumatoid arthritis. Merck has not commented on whether it intends to challenge the new Enbrel patent.