During prosecution of its patent application covering TRUSOPT, Merck filed a terminal disclaimer to voluntarily cut-short the duration of its patent's validity. The terminal disclaimer helped Merck overcome some of its own prior-art that might have obviated the invention. Later, because of delays in FDA regulatory approval, Merck was able to tack-on an additional 3+ years -- moving the expiry date from Dec '04 to Apr '08.
HI-TECH filed a Paragraph IV certification requesting approval for a generic version of the glaucoma treatment and asserting that Merck's patent was expired and invalid. The district court dismissed the case -- holding that the Hatch-Waxman term-extension was not canceled by the terminal disclaimer.
Law: 35 USC 156 provides that the term of a patent "shall be extended ... from the original expiration date of the patent" if the proper conditions are met. Section 156 makes no mention of terminal disclaimers.
Holding: On appeal, the CAFC found that it is permissible -- and in-fact mandatory -- to tack-on Section 156 extensions to the term of a terminally disclaimed patent.
Analysis: The statute says the term "shall be extended." That wording implies a duty to extend once the requisite conditions are met. According to the CAFC, since a terminal disclaimer is not an explicit exception to the rule, it cannot be read-in. This reading of the statute is buttressed by the fact that terminally disclaimed patents are explicitly excluded from 154(b) term adjustments. (expressio unius).