The Subject matter Suit pertains to infringement of Plaintiff's patent under Indian Patent No. 298645 (IN 645). The subject matter Suit relates to claim construction of a process patent and applicability of Doctrine of Equivalence in this regard.

The Plaintiff filed the subject matter Suit basing it's right in IN 645 which was a process Patent. The allegation of the Plaintiff in this case was that the Defendant was infringing the process patent of the Plaintiff. On the other hand, the defendant was, off course denying the infringement of the process Patent of the Plaintiff. This was the issue which was to be decided by the Hon'ble High Court of Delhi.

Vide its Judgement dated 19.09.2022 passed in Suit bearing CS COMM 349 of 2022 , the Hon'ble High Court of Delhi, in the matter titled as FMC Corporation and Ors Vs Natco Pharma Limited not with dealt with the issue of applicability of doctrine of equivalence in a process patent but also clarified this position as to what weightage has to be given to expert opinion of Scientific advisers appointed by the Court.

The subject matter Indian Patent No. 298645 (IN 645) was granted by the Controller of Patents, in favour of the Plaintiff on 06.12.2005. As per assertion of the Plaintiff, this Patent was a novel method for preparing "anthranilic diamide insecticide compounds" with a total of 12 claims.

This Patent was a process Patent for preparing "anthranilic diamide insecticide compounds" in which a carboxylic acid compound, an aniline compound and a sulfonyl chloride are combined together.

This case was filed against the Defendant alleging that the Defendant was also using similar method of activation of carboxylic acid moiety, in substantially the same way, i.e., coupling of carboxylic acid with aniline to achieve the same result, i.e., yield CTPR.

However the Defendant denied by asserting that in the Plaintiff's Patent, sulfonyl chloride is used as reagent for coupling carboxylic acid intermediate with aniline intermediate in a single step.

While Defendant's process involves two separate and discrete stages , carboxylic acid intermediate is converted to an acid chloride using thionyl chloride in a first reactor and the bio-products so formed viz. SO2 and HCl gases are scrubbed in caustic soda solution to give NaCl and NaHSO3, which are useful in food and cosmetic industries.

Then acid chloride of this step is reacted with amide intermediate in a second reactor to obtain CTPR. Thus allegation of infringement of Patent was denied by the Defendant.

The Plaintiff invoked the doctrine of equivalence to allege that even if the Defendant's process does not literally infringe the suit patent, it may be found to infringe on the bedrock of 'equivalence. The Doctrine of Equivalents mandates that in the absence of literal infringement, a product may be found to infringe a patented product, if it is found to be its substantial equivalent.

While Defendant was asserting that element to element test has to be applied. The basic foundation of the Defendant argument was that the reagent used by the Plaintiff in the subject matter Patent i.e. sulfonyl chloride was an essential element in Plaintiffs' process, on the contrary the Defendant uses thionyl chloride as the reagent.

Now the question was that , whether the Defendant can evade the doctrine of equivalence as alleged by the Plaintiff by relying upon this fact that the reagent used by the Plaintiff in their Patent was sulfonyl chloride and that the reagent used by the Defendant is thionyl chloride , which is different.

The Hon'ble High Court of Delhi summarized the applicability of Doctrine of Equivalence as advanced by the Plaintiff and Doctrine to element to element test, as argued by the Defendant by observing that the Doctrine of Equivalents must be applied to individual elements of the claim and an analysis of the role played by each element in the context of the specific patent claim will thus inform the enquiry as to whether a substitute element matches the function, way and result of the claimed element or whether the substitute element plays a role substantially different from the claimed element.

In such a situation , the role of different reagent applied by the Plaintiff in their process became important. For this Scientific advisors were appointed by the Hon'ble High Court of Delhi , who given their finding to the effect that sulfonyl chloride is an essential element of the suit patent. Thionyl chloride used as a reagent in the Defendant process, differs from sulfonyl chloride in its physical and chemical properties.

As Scientific advisers gave their finding to the effect that the essential element used by the Plaintiff and the Defendant in their respective Patent and respective product , i.e. sulfonyl chloride and Thionyl chloride are different in their physical and chemical property, the natural consequence would be that allegation of infringement has to fail.

The Hon'ble observed that weightage of of Scientific advisers has to be given and that Courts are not experts and should not substitute their views or opinion for those of the experts or specialists in the field. Thus Court declined the injunction to the Plaintiff as the Plaintiff was unable to establish that the process used by the Defendant in their product was equivalent to the Suit Patent Process.

From the afore mentioned discussion it is apparent that in cases pertaining to Process Patent, the Plaintiff is required to establish that the process used by the Defendant in its product is equivalent to the process used in the Plaintiff's Process Patent.

Doctrine of Equivalent does not require the element to element comparison of Plaintiff's and Defendant's Process. What court is required to see whether the essential feature of Defendant's process and Plaintiff's process are same or different? In doing so , the trifling differences has to be ignored. Thus if the Defendant imitates the essential feature of the Plaintiff's Process Patent then the same falls within the trap of Doctrine of equivalence.

Case Law Discussed:
FMC Corporation and Ors Vs Natco Pharma Limited
Judgement Date:19.09.2022
Case No. CS [COMM] 349 OF 2022
Hon'ble High Court of Delhi: Jyoti Singh, H.J.


Written By: Ajay Amitabh Suman, IPR Advocate, Hon'ble High Court of Delhi.
[email protected], 9990389539