A US appeals court has ruled that the expiration dates of two patents owned by Gilead that protect Tamiflu (oseltamivir) are important when determining whether they overlap with each other. If the generics manufacturer Natco is successful in the next stage of the dispute, the company may be able to file for regulatory approval of generic oseltamivir 22 months earlier than originally anticipated.

Credit: Aloysius Patrimonio/Alamy

Natco asserted that Gilead had committed so-called obviousness-type double patenting (OTDP) with regard to two Tamiflu patents (US 5763483 and US 5952375). This doctrine prevents an unjust extension of the length of patent protection by stating that the claims of one patent must be distinct from the claims of a second patent (that shares a common inventor). Normally, the reference patent on which OTDP is based issues before and expires before the second patent. But in the current case, the court had the unusual task of deciding whether a patent (the '375 patent) that expires before yet was issued after another patent (the '483 patent, which expires 22 months after the '375 patent) qualifies as a reference for OTDP.

In agreeing with Natco, the court said that expiry dates as well as issuance dates should be taken into account when deciding OTDP; therefore the '375 patent could serve as a double patenting reference for the '483 patent even though it was issued later. Relying only on the issuance date, said the court, could create quirks in the patent system, meaning that a patentee could then circumvent the intended purpose of OTDP and obtain an unwarranted patent extension.

The appeals court remanded the case to a district court to decide whether the '483 patent overlaps with the '375 patent.

Gilead et al . versus Natco