Grant of a patent gives the patentee exclusive rights to prevent others from developing, using, or selling the patented product or process without authorization. In order to claim granted patent rights, an inventor must show that the product or process is novel, non-obvious and capable of commercial application. The application for registration of a patent also needs to set out specific claims identifying the elements of the product or process over which the inventor desires exclusivity. In order to claim infringement of a granted patent, the patent holder or anyone claiming under it needs to show that all the essential elements of the patent are being infringed.

However, a close imitation or rather, a similar invention with similar claims that performs the same functions as the original one, may not fall under the ambit of ‘infringement'. Yet, such exploitation essentially vitiates the objective of providing an inventor with exclusivity over their patent. A strict and literal construction of the contents of a patent claim virtually allows an infringer to find ways around the claims. In order to safeguard the rights of an inventor and provide relief for such matters, courts developed the doctrine of equivalents, allowing them to hold a party liable for infringement for the use of elements, which although not part of a claim in a granted patent, were equivalent to them in a subsequent application made.

The doctrine of equivalents was developed by the United States Supreme Court in Winans vs. Denmead1 , observing that infringement of a patent could occur in cases where the infringer had tried to avoid the literal language of a claim, but the resultant product or process was equivalent to the original invention, if not exactly the same. Subsequent judgments saw the evolution of this doctrine, with the United States Supreme Court laying down the ‘triple test'2 and ‘all elements test' 3 to determine potential “indirect” infringement of patents.

The doctrine, although not dealt with specifically in India, has been recognized by the courts on several occasions. The Delhi High Court in Raj Parkash vs. Mangat Ram Chowdhry4 applied the doctrine of pith and marrow, observing that even if there was no direct infringement of patent claims, an action for infringement would succeed if the pith and substance of patented subject matter was replicated. The concept was formally recognized by Indian Courts in Ravi Kamal Bali vs. Kala Tech, with the Bombay High Court observing that mere superficial difference or existence of altered non-essential elements could not distinguish a product from a patented invention.5


More recently, the Delhi High Court reiterated the doctrine of equivalents in FMC Corporation vs. Natco Pharma Limited, denying FMC Corporation's (“FMC”) claim for patent infringement against Natco Pharma Ltd (“Natco”). FMC registered a process patent bearing no. 298645 (“IN' 645”/ “Suit Patent”) for “Method for preparing N-Phenylpyrazole-1-Carboxamides” along with several other patents related to the manufacture of Chlorantraniliprole (“CTPR”). 

FMC filed a suit for infringement of its patent IN' 645 by Natco6 before the High Court of Delhi alleging that Natco's patent application bearing no. PCT/IN2019/050321 (“Natco's patent application”) with claims for a “method of preparing CTPR”, were equivalent to its claims made under IN'645. Vide order dated September 19, 2022, the Ld. Single Judge refused to grant ad-interim injunction in FMC's favor.7 The Ld. Single Judge had prima facie observed that Natco had made use of thionyl chloride in the process, whereas FMC Corporation had claimed a process utilizing sulfonyl chloride. Such difference, in the eyes of the Ld. Single Judge, was not “minor or insubstantial”. Aggrieved by the order dated September 19, 2022, FMC Corporation filed an appeal before a Division Bench of the High Court of Delhi.

FMC, although admitting that the process used by Natco (“Natco's Process”) was not identical to claims made in IN'645, submitted that due to application of the doctrine of equivalents, Natco's Process infringed their patent. FMC reiterated that the changed reagent i.e., the usage of sulfonyl chloride was not essential to IN'645 and Natco's Process was thus equivalent to the suit patent i.e. IN'645 as it performed substantially the same function.

In response, Natco argued that FMC's actions amounted to ever-greening of their expired patent rights. It was submitted by Natco that the process claimed in its patent application is different as it is a twostep process requiring two reactors and unlike IN'645, its patent application did not produce any toxic by-products. Such dissimilarities, stated Natco, could not be considered as non-essential. Furthermore, Natco also averred that the scope of equivalents was limited in case of process patents.

While rejecting the Appeal filed by FMC, the Division Bench refused to interfere with the findings of the Single Bench. It was observed by the Division Bench that the “doctrine of equivalents, in essence, seeks to address infringers who introduce minor variations as subterfuge to defeat patent rights. The doctrine is applied to ascertain whether there is an infringement by excluding any insubstantial, minor, or trivial changes that are designed to deprive the patentee of the benefits of his invention”. The Court also discussed whether equivalents are required to be determined by applying the triple test - the function served by a particular element; the manner in which the function is performed; and the results obtained by the element - or by applying the test whether the differences are substantial. A device which substantially performs the same function, in substantially the same way, and accomplishes the same result, may infringe the patent rights. However, when it comes to a process or a method, this test may require to be suitably adapted. In a case where a method of achieving a result is the essence of the patent, achieving substantially the same result would clearly not be relevant. The method with which the result is obtained would be material to determine whether the patent has been infringed.

The Division Bench, applying the triple test to processes, observed that the test of substantial identity of the competing methods must necessarily be viewed by identifying the essential elements and steps of the said process and then examining the manner in which the key elements interact in each essential step that the process/method entails to yield the given result. The Court also observed that the doctrine of equivalents had to be applied to each element of the process.

Upon introspection, the Court concluded that sulfonyl chloride was essential to Natco's process as it resulted in high yields. Additionally, it was specifically mentioned in the claims and thus, had to be treated as an essential component of the process. This view was further exacerbated by the acute differences in process, specifically due to the two-step nature of the Natco's Process. Upon a comparison of the two processes, the Division Bench concurred with the judgment of the Ld. Single Judge, dismissing FMC's appeal.


In a significant ruling, the Single Bench as well as the Division Bench have contributed to the growth and evolution of the doctrine of equivalents in India. The Division Bench, rightly recognizing the limited applicability of the triple test to processes, adapted and laid down a more suitable test, thereby setting precedent for the comparison of processes and methods. While the doctrine of equivalents although has been validated by Courts worldwide, was not examined in detail by the Indian Courts till this case. The judgment of the Division Bench has also provided more clarity on the test for essentiality of elements of a process, streamlining the path for future matters along similar lines.

However, the Single Bench as well as the Division Bench have seemingly taken a very strict approach to the interpretation of FMC's claims. Although the claims specifically mentioned that the process could occur in any sequence, the Court used the “most preferrable” sequence as mentioned in the claim for comparison and restricted FMC's claim accordingly. Considering this narrow interpretation, it becomes important to be wary of mentioning preferred sequences in claims and such observations may pose a hurdle to several registered process patents, should infringement be tested per the doctrine of equivalents.


1 Winans v Denmead, 56 U.S. 330 [1853]

2 Graver Tank & MFG Company v Linde Air Prods Inc., 339 U.S. 605 [1950]

3 Warner-Jenkinson Co., Inc v Davis Chemical Co., 520 U.S. 17 [1997]

4 ILR (1977) 2 Del 412

5 Ravi Kamal Bali v Kala Tech & Ors, (2008) 38 PTC 435

6 FMC Corporation & Ors. vs Natco Pharma Limited, CS (COMM) 349/2022

7 2022 SCCOnLine Del 2994

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