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Introduction

In February 2026, the Division Bench of the Delhi High Court delivered a landmark judgment in Boehringer Ingelheim Pharma GmbH v. Controller of Patents & Anr. (LPA 129/2025). The case dealt with two important questions of patent law. First, whether a revocation petition under Section 64 of the Patents Act, 1970 can survive after the petitioner has already pleaded invalidity of the patent as a defense under Section 107(1) in an infringement suit. Second, whether such a petition can continue after the patent itself has expired. The Court held that revocation petitions are independent remedies, distinct from defenses under Section 107, and that they remain maintainable even after the expiry of the patent.

Facts of the Case

Boehringer Ingelheim was granted Indian Patent (IN 243301) on 21 August 2022 for the pharmaceutical product Linagliptin. On 17 February 2022, Macleods Pharmaceuticals filed a revocation petition under Section 64(1) of the Patents Act before the Delhi High Court, seeking to revoke Boehringer’s patent. Two days later, on 19 February 2022, Boehringer filed an infringement suit against Macleods in the Himachal Pradesh High Court. In its written statement in that suit, Macleods raised invalidity of the patent as a defense under Section 107(1).

The patent expired on 18 August 2023 by efflux of time. Boehringer then filed applications before the Delhi High Court seeking dismissal of the revocation petition. It argued that the petition was barred because Macleods had already raised invalidity under Section 107 in the Himachal suit, and further that the petition could not survive once the patent had expired. On 15 January 2025, a Single Judge of the Delhi High Court dismissed Boehringer’s applications, holding that revocation and invalidity defenses are distinct, and that revocation petitions survive expiry of the patent. Boehringer appealed this decision to the Division Bench.

Argument in Favour

Macleods Pharmaceuticals argued that the revocation petition was maintainable despite the Section 107 defense and despite the expiry of the patent. It submitted that revocation under Section 64 operates retrospectively, effacing the patent from the register as if it never existed. By contrast, a Section 107 defense only operates between the parties in the suit. Macleods emphasized that Section 64 refers to “a patent” and not “a patent in force.” The legislature did not restrict revocation petitions to live patents, and the Court should not supply words that Parliament omitted.

Macleods further argued that even after expiry, the patentee can sue for damages for past infringement. Therefore, the defendant remains a “person interested” under Section 2(1)(t), with a real interest in seeking revocation to shield itself from damages. It stressed that Section 107 is a shield, while Section 64 is a sword, and the Act does not prohibit pursuing both remedies unless a counter-claim has already been filed. Finally, Macleods relied on Section 151 of the Patents Act, which distinguishes between entries made in the register upon revocation (removal of the patent) and entries made upon invalidity findings in suits (supplemental record). This distinction, it argued, shows that both remedies serve different purposes.

Argument Against

Boehringer contended that the revocation petition was unsustainable. It argued that once a patent expires, it ceases to exist, and revocation of an expired patent is meaningless, akin to “flogging a dead horse.” A patent only grants monopoly while alive, and after expiry the invention enters the public domain, making revocation unnecessary. Boehringer also warned that allowing both a Section 107 defense and a revocation petition would lead to conflicting judgments in different courts and unnecessary duplication of litigation.

Boehringer relied on Aloys Wobben v. Yogesh Mehra [(2014) 15 SCC 360], where the Supreme Court held that once an infringement suit is filed, the defendant must either raise invalidity under Section 107 or file a counter-claim; a separate revocation petition is barred. It also cited Ajay Industrial Corporation v. Shiro Kanao of Ibaraki City [AIR 1983 Del 496] and Star Textile Engineering Works Ltd v. James Mackie Holding Ltd [1977 SCC OnLine Cal 280], arguing that revocation after expiry is impermissible.

Court’s Decision

The Division Bench dismissed Boehringer’s appeal and upheld the Single Judge’s findings.

On the issue of patent expiry, the Court held that revocation operates retrospectively, wiping out the patent from the date of grant. Since patentees can claim damages for past infringement even after expiry under Section 108, defendants retain a live interest in seeking revocation to invalidate such claims. The Court noted that Section 2(m) defines “patent” as “a patent for any invention granted under this Act,” which does not require the patent to be currently in force.

On the issue of Section 107 versus Section 64, the Court clarified that Section 107 is a defense in personam, affecting only the parties in the suit. Success under Section 107 results in dismissal of the suit but does not remove the patent from the register. Section 64 revocation, by contrast, operates in rem, removing the patent entirely from the register and preventing assertion against any party. The Court distinguished Aloys Wobben v. Yogesh Mehra, holding that the bar applies only when a counter-claim has been filed, not when invalidity is merely pleaded under Section 107.

The Court relied on Virgin Atlantic Airways Ltd v. Zodiac Seats UK Ltd [EWCA Civ 1062], which supported the principle that revocation operates retrospectively and in rem. It also considered Star Textile Engineering Works Ltd v. James Mackie Holding Ltd [1977 SCC OnLine Cal 280], but held that revocation of expired patents is not barred. Ajay Industrial Corporation v. Shiro Kanao of Ibaraki City [AIR 1983 Del 496] was discussed but not accepted as binding precedent against revocation of expired patents.

Conclusion

The Delhi High Court’s ruling in Boehringer Ingelheim Pharma GmbH v. Controller of Patents & Anr. is a landmark clarification of patent law. The Court affirmed that revocation petitions under Section 64 are standalone remedies, distinct from defenses under Section 107. It held that revocation petitions survive even after the expiry of the patent, because they operate retrospectively and in rem, effacing the patent from the register as if it never existed. Defendants retain a live interest in pursuing revocation to shield themselves from damages claims for past infringement.