Daniel Kazhdan


At least since 1819, courts have prohibited double patenting—where an inventor has two patents on the same or obvious variations of the same invention. There have always been two basic justifications for prohibiting double patenting. The first focused on the patentee: bad actors might try to improperly extend their patent monopoly by filing serial applications. The second focused on the public’s rights: the bargain of the patent is that in exchange for the inventor getting a term-limited patent, the public is entitled to use the claimed invention (and its obvious variations) once the patent expires. This public-rights rationale is broader, and it applies independent of whether the patentee’s filing of serial applications allows her to extend the patent term.

The patentee-based justification had more purchase in the olden days—when a patent’s term was determined by its issue date. Every new patent that issued would get a new term. Since 1995, though, a patent’s term is 20 years from the earliest effective filing date—a date that stays the same independent of whether the inventor strings out her patent applications—so the inventor cannot really game the system. On the other hand, the public still cannot receive the fruit of its bargain if it cannot use a claimed invention as soon as a patent expires.

The previously low-stakes debate about the reason for prohibiting double patenting now matters. Most significantly, is there a double-patenting problem for a parent patent where the parent gets patent-term adjustment, but the child does not? On the patentee-based justification, there may well not be a problem for the parent, but on the public-rights based justification, there would be. Inventors that receive patent-term adjustment on a parent patent have to decide whether to pursue continuation applications, as continuation applications are likely to not receive the same amount of adjustment. Depending on how the law on double patenting evolves, the continuation patents may cut short the term of the parent patent—what this article will call patent patricide. For patents on pharmaceutical drugs, the question of patent patricide can be worth billions of dollars.