Case law has defined prosecution laches as an affirmative defense against an infringement assertion. Specifically, the case law indicates a patent that is being asserted is unenforceable when the patentee caused an unreasonable and unexplained delay in prosecution of the patent. Symbol Tech v Lemelson Medical, No. 04-1451 (Fed. Cir. 2005). There is relatively little case law on the specifics of laches. However, in 2021, the Federal Circuit said: “we now hold that, in the context of a § 145 action, the PTO must generally prove intervening rights to establish prejudice, but an unreasonable and unexplained prosecution delay of six years or more raises a presumption of prejudice”. Gil Hyatt v. Hirshfeld (Fed. Cir. 2021). What does this – or might this – mean beyond the Hyatt case? The pharmaceutical area may provide an insightful perspective on the potential reach of this dicta, given that pharmaceutical patents are frequently relied upon to at least partly justify billions of dollars of investment for research and development. Therefore, this study investigates patents that were listed in the Orange Book or Purple Book as protecting the top 20 pharmaceuticals, in terms of revenue.

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