On April 22, 2014, the US Court of Appeals for the Federal Circuit issued an opinion in Gilead Sciences, Inc. v. Natco Pharma Ltd., vacating the US District Court for the District of New Jersey's ruling that Gilead's later-issued but earlier-expiring patent could not qualify as an obviousness-type double patenting reference that could limit the term of Gilead's later-expiring patent (No. 2013-1418, (Fed. Cir. Apr. 22, 2014)).

Gilead owns US Patent Nos. 5,763,483 ('483 patent) and 5,952,375 ('375 patent). Both patents are directed to antiviral compounds and methods of use and have substantially similar disclosures. However, the patents do not claim priority to a common patent application and, therefore, have different expiration dates, with the '483 patent expiring 22 months after the '375 patent. After the '483 patent issued, Gilead filed a terminal disclaimer in the application that led to the '375 patent, disclaiming any portion of the '375 patent term that extended past the expiration date of the '483 patent. Gilead did not, however, file a terminal disclaimer for the '483 patent in view of the '375 patent.

Gilead sued Natco for infringement of the '483 patent under the Hatch-Waxman Act after Natco filed a request with the US Food and Drug Administration to market a generic version of Gilead's Tamiflu product. In defense, Natco asserted that the '483 patent was invalid for obviousness-type double patenting over the '375 patent. Gilead responded that the '375 patent could not serve as a double patenting reference because the '375 patent issued after the '483 patent, even though the '375 patent expired 22 months before the '483 patent. The district court agreed with Gilead and entered the parties' stipulated judgment of infringement. Natco appealed.

On appeal, Gilead argued that the '375 patent could not serve as a double patenting reference because:

The Federal Circuit rejected Gilead's argument and held that a patent that issues after but expires before another patent can qualify as a double patenting reference. The court reasoned that:

In his dissent, Chief Judge Rader objected to the court's expansion of the doctrine of obviousness-type double patenting. Rather than creating a new rule to address this novel situation, he would not have applied the double patenting doctrine at all because the case did not raise the typical concerns the doctrine is meant to address, including:

Judge Rader also noted that, by not claiming priority to the '375 patent family, Gilead gave up roughly ten months of priority for the '483 patent. As part of the bargain, Gilead should be afforded the extra 22 months of the '483 patent's exclusivity beyond the '375 patent.