A recent ruling from one of India’s High Courts offers a reminder that a position taken to secure a patent cannot be walked back during its enforcement.
What was once optional became essential
In the original patent application, a dyeing agent was included only in a dependent claim. But when faced with novelty and inventive step objections by the patent office during prosecution, the plaintiff amended the claims and incorporated the dyeing agent into the independent claims. It was now framed as solving a real-world problem by helping farmers visually confirm herbicide application. This strategic amendment then helped distinguish the invention from cited prior art and secure the patent.
Reinforced again to survive post-grant opposition
In post-grant opposition proceedings by an opponent, the plaintiff again relied on the dyeing agent to differentiate the claimed invention from cited prior art. This consistent narrative solidified the dyeing agent’s role as an essential element.
A reversed stance in enforcement
Later, when initiating infringement proceedings against a competitor whose product did not contain the dye, the plaintiff changed course. The dyeing agent was now described as non-essential, an adjuvant at best. The plaintiff invoked the Doctrine of Equivalents to argue that the defendant’s product still fell within the scope of the patent, even without the component it had previously emphasized.
Why the Court refused to follow
The Court rejected this stance, citing prosecution history estoppel. Plaintiff’s prior reliance on the dyeing agent during prosecution and opposition bound them to its essentiality. “The plaintiff cannot be allowed to approbate and reprobate,” the court ruled, denying the interim injunction.
Strategy across the patent lifecycle must align
This ruling reinforces a practical truth that claim amendments and prosecution arguments are not temporary tactics. They shape the enforceable scope of a patent. A feature relied on to overcome prior art becomes part of the patent’s identity. It cannot be discarded when the enforcement strategy demands broader coverage.
You truly can’t have your patent cake and eat it too.
Case: Crystal Crop Protection Limited v. Safex Chemicals India Limited [May 07, 2025]
