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
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
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
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 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
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
, 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
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
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
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