The Interplay of Patent Term Extension (PTE) and Reissue: Merck v. Aurobindo and Its Implications, Part II

As discussed in our preceding article, the Federal Circuit in Merck Sharp & Dohme B.V. v. Aurobindo Pharma USA, Inc., 130 F.4th 1363 (Fed. Cir. 2025), concluded that Patent Term Extension (PTE) for a reissue patent that originally contained claims covering an approved drug product, and which was reissued to include narrower claims to that drug product, should have the term extension under 35 U.S.C. § 156 calculated using the issue date of the original patent, not the issue date of the reissued patent. However, a patent holder may file a reissue application for reasons not addressed in Merck. This article explores such alternative grounds for reissue and considers the potential applicability of Merck in those scenarios.

As one example, a patent holder may reissue a patent to correct misjoinder of inventors. See Ex parte Scudder, 169 U.S.P.Q. 814, 815 (B.P.A.I. 1971) (holding that 35 U.S.C. § 251 authorizes reissue to correct misjoinder where the remedy of 35 U.S.C. § 256 is inadequate). Alternatively, a patent holder may pursue reissue to add claims containing features not recited in the original claims as a “hedge against possible invalidity of” those original claims. See In re Handel, 312 F.2d 943, 945 n.2 (C.C.P.A. 1963).

Merck did not address whether its holding would apply to patents that are reissued under the conditions described above, which may similarly raise the question of whether the original issue date or the reissue date should be used to calculate PTE under 35 U.S.C. § 156. Nevertheless, the Merck court’s reasoning suggests that the original issue date should be used in each of these scenarios—at least, as long as both the original patent and the reissued patent include a claim directed to the approved drug product for which PTE is sought. Specifically, when the court concluded that, “in the context of reissued patents, ‘the patent’ in subsection 156(c) refers to the original patent,” it constrained that conclusion to an “original patent that includes claims that are directed to [an approved] drug product” (130 F.4th at 1372) (emphasis added), as Merck’s ’340 patent did. The court remarked that “[d]ifficult questions arise in cases where the original patent did not include any claims directed to the drug product and was later reissued to include broader claims directed to such products,” but it acknowledged that “[t]hose questions are not presented” by the Merck case itself. 130 F.4th at 1372, n.11.

Aside from imposing the requirement that both the original patent and the reissue patent contain claims directed to the FDA approved drug product, Merck did not appear to restrict its conclusion to a particular basis for pursuing reissue. Indeed, the court’s statutory construction analysis focused on subsection 156(c), which is part of the PTE section of the patent statute, not one of the reissue sections, and on Congress’s intent in drafting Section 156. Merck, 130 F.4th at 1368-72. Additionally, the court emphasized that the PTE statute “should be liberally interpreted to achieve [the] end” of “a patentee receiving time lost in its patent term by reason of FDA delay” (id. at 1370 (quoting Merck & Co. v. Kessler, 80 F.3d 1543, 1552 (Fed. Cir. 1996)), a rationale that may also support applying Merck’s holding to alternative reissue fact patterns.

The Merck court also acknowledged that guidance in Section 2766 of the Manual of Patent Examining Procedure (M.P.E.P.), though not binding on the court, “substantially tracks” with its analysis. Id. at 1372. With respect to calculating the amount of PTE to which a reissue patent is entitled, Section 2766 states “so long as the original patent claimed the approved product and the reissued patent claims the approved product, the original patent grant date would be used to calculate the extension to which the reissued patent would be entitled.” Section 2766 does not limit that reasoning to any specific basis for reissuing a patent. Thus, the Merck court’s embrace of Section 2766—which the court stated “comports with the statutory scheme of the Hatch-Waxman Act” (Merck, 130 F.4th at 1372)—further suggests the court’s reasoning may extend beyond the scenario where a patent is reissued solely to add dependent claims.

In yet another scenario, a patent owner may cancel original claims outright and replace them with a set of narrower claims. The Federal Circuit addressed that situation in In re Rosuvastatin Calcium Patent Litigation, 703 F.3d 511 (Fed. Cir. 2012), which involved U.S. Pat. No. 5,260,440 (“the ’440 patent”), which was reissued as RE37,314 (“the RE’314 patent”). The ’440 patent’s claims related to HMG-CoA reductase inhibitors, including rosuvastatin. The calcium salt of rosuvastatin is the active ingredient in Crestor®, the regulatory review of which gave rise to PTE for the RE’314 patent. Id. at 514-516, 519. The ’440 patent issued with genus claims, but, during reissue, the patent holder cancelled all of the original claims and introduced new claims narrowly directed to rosuvastatin. Id. at 535. Reasoning that the patent holder “had the right to a reissue in which it claimed only rosuvastatin and its salt,” the Federal Circuit concluded that the scope of the reissue was in accordance with the law. Id. at 524, 527.

The Merck court recognized one reissue scenario where Section 156 “would not apply,” which is where an “original patent included claims directed to a drug product subject to regulatory review and the patent owner subsequently cancels those claims.” Id. at 1372, n.10. The court’s statement could be interpreted to mean that, if original claims directed to drug product are cancelled during reissue and new claims directed to that drug product are added—as occurred in In re Rosuvastatin Calcium Patent Litigation—then the reissued patent is ineligible for PTE. However, that interpretation would be inconsistent with both M.P.E.P. § 2766 and the Merck court’s statement that the PTE statute “should be liberally interpreted” to compensate a patent holder for patent term loss occurring “by reason of FDA delay” (Merck, 130 F.4th at 1370). Additionally, while that issue was not the subject of In re Rosuvastatin Calcium Patent Litigation, the prosecution of the RE’314 patent fits that fact pattern, and the RE’314 patent received PTE. Moreover, the term extension for the RE’314 patent was calculated using the original issue date of the ’440 patent.

We instead interpret the Merck court’s footnote remark as describing a circumstance where an original patent claimed a drug product and, during reissue, those claims were cancelled without adding new claims to the drug product. That scenario would not meet the requirement, set forth in both Merck and M.P.E.P. § 2766, that both the original and reissued patents claim the drug product. Nor would it meet the statutory requirement of 35 U.S.C. § 156(a) that a patent (whether original or reissued) must claim “a product, a method of using a product, or a method of manufacturing a product” to qualify for PTE in the first place. Thus, we assume it was this scenario, in which a patent originally contained claims covering an approved product but no such claims remain after reissue, that the Merck court was contemplating in its footnote remark.

Merck provides patent owners with clarity regarding the proper calculation of PTE for a patent that claims a drug product and is reissued to add narrower claims to that drug product.

While we consider it likely that the Merck holding will be applied to additional reissue scenarios, for example, to those discussed herein, we will continue to monitor this intersection of PTE and reissue case law, including whether district courts and the Federal Circuit apply Merck to situations where a patent is reissued on different grounds.