There are dozens of ways a patent can be invalidated or rendered unenforceable. Some of these may be best characterized as "traps" that could be readily avoided but are nevertheless often discounted or ignored. Among these is the Double Patenting Trap - a situation that arises when the USPTO grants an applicant more than one patent on the same invention or on patentably indistinct inventions without a pre-issue terminal disclaimer or 35 USC §121 "safe harbor" exception. Most commonly, the double patenting trap occurs in: large application families (applications having multiple continuations, divisionals, CIPs); big projects having multiple applications with overlapping disclosures; and companies spreading disclosures among multiple outside law firms. Practitioners often fail to take the double patent issue seriously, but they should!

A former client got embroiled in a cross-licensing negotiation with a large competitor. Among the stack of patents involved was a strong, broad patent covering a valuable segment of the market. Unfortunately, they also had a prior patent that had different inventors, a different practitioner, a different examiner, ... and broad claims giving rise to a statutory double patenting problem. It was sloppy work, creating potential grounds for inequitable conduct and a significant degree of embarrassment for the competitor. Those patents disappeared from the negotiation - no concessions required!

That was the first time I saw what I considered to be a good patent killed by the Double Patenting Trap. But it wasn't the last! I urge my clients, trainees, and colleagues to be vigilant on this issue. Don't just assume that the examiner will catch it, and don't forget to disclose related applications even when they aren't "prior art" -- they can still be "material to patentability".

The first type of double patenting is "same scope" or "statutory double patenting". Two patent claims have the same scope when any invention embodiment that infringes either of the two patent claims also infringes the other of the two patent claims. It is easy to avoid if you're paying attention, but practitioners should beware synonyms or different phrasing that amounts to the same scope. Statutory double patenting cannot be cured with a terminal disclaimer.

The second type of double patenting is "nonstatutory double patenting" (NDP). There are 3 tests for NDP: anticipation, one-way obviousness, and two-way obviousness. NDP IS curable with a terminal disclaimer IF: (1) common ownership or common enforcement can be assured; (2) if the disclaimer is for the later-expiring patent; AND (3) if filed before issuance of the later patent.* Alternatively, it can be avoided by canceling the duplicative claims during prosecution.

 *With regard to requirement (3) above, it is unclear whether a terminal disclaimer after the issuance of the second patent will serve to cure NDP. The USSC precedent Miller v. Eagle Mfg Co., 151 U.S. 186, 198 (1894) clearly states that the "second patent is void". However, that precedent predates the 1952 Patent Act, which created terminal disclaimers (35 USC §253). (The 1952 Patent Act also specifies that any invalidity analysis must be performed on a claim-by-claim basis rather than treating each patent as a whole.) The 1952 Patent Act itself has no mention of NDP, but in testimony to congress one of the Act's authors suggested that terminal disclaimers might address one of the reasons the courts created the NDP doctrine. Before the Federal Circuit was created, some appeals courts found post-issue terminal disclaimers to be ineffective at curing NDP, but the Federal Circuit has indicated in dicta that post-issue terminal disclaimers should be effective. Perricone v. Medicis Pharm. Corp., 432 F.3d 1368, 1375 (Fed. Cir. 2005) (suggesting a post-issuance terminal disclaimer can cure NDP); Boehringer Ingelheim Int'l GmbH v. Barr Labs., Inc., 592 F.3d 1340, 1347 (Fed. Cir. 2010) (“Even where a patent is found invalid for obviousness-type double patenting, … a patentee may file a terminal disclaimer”); Eli Lilly & Co. v. Teva Parenteral Medicines, Inc., 845 F.3d 1357, 1375 (Fed. Cir. 2017) (quoting Perricone and Boehringer). Yet, as noted in Chisum on Patents 3A 9.04[4][b] (2023), "No decision considers squarely whether a terminal disclaimer entered after the issuance of the second patent will cure a double patenting objection.” When squarely faced with this issue, the Federal Circuit may well find that the facts of the case dictate against a cure. Chisum echoes one commentator “The net effect of an unreasonable delay in filing a terminal disclaimer may … be a form of the very ‘extension of monopoly' the terminal disclaimer provision was intended to avoid.” Id.

A recent Federal Circuit case departs with the long-held view that the double patenting trap only operates against the later-issued patent. In Gilead Scis. v. Natco Pharma Ltd., 753 F.3d 1208 (Fed. Cir. 2014), the court held the first issued patent invalid for NDP over the later-issued patent on the basis that the first-issued patent was also the later-expiring patent and in their view the analysis should be based on expiration date rather than issue date. This holding is at least arguably inconsistent with USSC precedent, as the Underwood v. Gerber, 149 U.S. 224 (1893) held the second patent invalid even though it did not extend the patent monopoly. In any case, the Federal Circuit even more recently moved to limit the scope of the Gilead holding to only cases from different patent families. Within a given family of related cases all entitled to the same priority date, the Gilead holding does not apply. Allergan v. MSN Labs., slip op. 24-1061 (Fed. Cir. 2024).

The evolution of double patenting case law raises uncertainties that most clients would prefer to avoid. The attendant issues are not necessarily limited to the second-issued patent, but can also raise enforcement concerns for the first-issued patent, particularly if the patents don't share identical inventorship and ownership/control. Even inconsistent statements in the prosecution histories may be a cause for concern, and an unreasonable delay in submitting any terminal disclaimers may create laches. I strongly recommend that any practitioners who may have been inattentive to double patenting issues immediately revise their drafting checklist and their pre-issuance review checklist to include considering the double patenting question in connection to any related patents having common ownership or a shared inventor.