Can MSN prevail on its patent appeal against Acadia for generic Nuplazid?

Zachary Silbersher

Acadia has been embroiled in a patent dispute with MSN Pharmaceuticals over a generic version of Acadia’s Parkinson’s Disease drug Nuplazid® (pimavanserin).  The lawsuit boiled down to a single dispute over a single legal issue concerning a single patent.  In December 2023, the district court ruled in favor of Acadia.  The case is now on appeal before the Federal Circuit. What are the chances of MSN prevailing on appeal? 

The Double-Patenting Doctrine

MSN’s appeal concerns the legal issue of double patenting.  None of the science behind Acadia’s pimavanserin drug or its patents are at issue in the appeal.  Double patenting is a comparatively esoteric doctrine on the fringes of patent law that rises periodically, but far from frequently.   

The double patenting doctrine prevents an inventor from owning more than one patent on either the same invention or an obvious variant of that invention.  Otherwise, patent holders could extend the monopoly life of one patent by obtaining a second patent—with a later expiration date—based on the same invention or an obvious variation thereof. 

The double patenting doctrine can therefore be used by generics to invalidate a patent asserted in a Hatch-Waxman litigation.  If brand pharmaceutical company owns two patents (Patent 1 and Patent 2) that are obvious variations of each other, and Patent 1 expires before Patent 2, then the double patenting doctrine can invalidate—or cancel—Patent 2 before its natural expiration date.  Rather, Patent 2 will be deemed to have expired as of the earlier expiration date of Patent 1.

Here, Acadia asserted the ‘740 patent against MSN.  The ‘740 patent covers the tartrate salt of pimavanserin.  Acadia also owns the ‘271 patent, which covers using pimavanserin tartrate to treat hallucination or delusion.  The ‘740 patent is not scheduled to expire for a couple years, whereas the ‘271 patent has already expired.  Courts have already held that a method of using an active ingredient compound is an obvious variant of the compound itself under the double patenting doctrine.

Accordingly, if the double patent doctrine applies, as argued by MSN, then the ‘740 patent should be deemed to have expired as of the expiration date of the ‘271 patent, which already happened.  The only issue in this appeal is whether the double patent doctrine applies. 

The Safe Harbor Provision 

The next wrinkle involves what’s called the safe harbor provision.  This is essentially an exception to the double patenting doctrine.  To understand the safe harbor provision requires understanding “restriction requirements” and “divisional applications.”  Wonky words, yes, but still fairly straightforward. 

A patent application must include a disclosure, where the invention is described at length typically using examples, tests, data, different embodiments and so forth.  At the end of the patent application, an inventor must also include “claims.”  The claims define precisely what contours of the patent covers.  The claims literally are the patented invention, whereas the disclosure (otherwise known as the patent’s specification) substantiates and describes different aspects of the invention that may or may not be included in the claims. 

It is not uncommon that a patent applicant will (deliberately or not) include more than one invention in patent application.  If the applicant then “claims” more than one invention, the Patent Office examiner will issue a “restriction requirement.”  The restriction requirement will identify the multiple different inventions that are claimed.  The applicant typically chooses one invention to pursue.  If she wants to pursue the other, unselected inventions, she can file a follow-on patent application, which is known as a divisional application.

Back to the safe harbor provision.  The safe harbor provision provides that, if an applicant for Patent 1 files a divisional application following a restriction requirement, then the patent resulting from that divisional application, which would be Patent 2, cannot be invalidated under the double patenting doctrine by Patent 1.

But wait!  If Patent 2 is a divisional of Patent 1, then presumably both patent applications can claim priority to the same filing date, and therefore, shouldn’t they both expire at the same time?  And if they both expire at the same time, then why would the double patenting doctrine matter at all?  Indeed, when the double patenting doctrine applies, it typically compels Patent 2 to expire earlier than it naturally would have if the doctrine did not apply. 

MSN’s arguments on appeal.

Good question!  The best way to answer that is to look at the patents in Acadia’s case against MSN.  Again, Acadia asserted the ‘740 patent against MSN, but MSN has argued that the ‘271 patent should be used as double patenting reference to cut short the expiration date of the ‘740 patent.  Both the ‘740 patent and the ‘271 patent claim priority to the same original parent patent application.  All else being equal, they should naturally expire at the same time.  

However, in this case, the ‘740 patent received nearly three additional years of patent life, whereas the ‘271 patent received no additional time.  (The ‘740 patent received additional patent life based on Patent Term Adjustment, which is awarded based on delays by the Patent Office, not based on anything meritorious about the patent itself.)  Thus, even though both patents claim priority to the same parent application filed in 2024, the ‘271 patent has already expired whereas the ‘740 patent continues to have roughly two more years of life.  (Very generally, the life of a patent is measured as 20 years from the filing date of the parent patent application, which in this case, was filed in January 2004.)

Here's where it gets complicated (although, it may already be complicated.).  The ‘740 patent (the compound for pimavanserin) was actually the first application to be examined by the Patent Office.  While the application for the ‘740 patent was pending, Acadia filed a follow-on application, which through a series of further follow-on application, eventually became the ‘271 patent. 

The ‘740 patent issued in October 2009, and the ‘271 patent issued in January 2010.  Therefore, the ‘740 patent issued before the ‘271 patent.  MSN is arguing that the ‘271 patent, which is already expired, should cut short the expiration date of the ‘740 patent, which has about two more years of life.  That’s technically backwards from what we described above.  In other words, the ‘271 patent is acting as Patent 1 and the ‘740 patent is acting as Patent 2, even though technically, the ‘740 patent (Patent 2) was filed first, and the ‘271 patent (Patent 1) was filed later.

Can the ‘271 patent cut short the patent life of the ‘740 patent?

The district court found this timing was a problem for MSN’s double patenting argument.  It held that a double patenting reference (Patent 1) cannot cut short the expiration date of patent that expires later (Patent 2) if Patent 1 was actually filed after Patent 2.

On appeal, MSN is arguing that this was reversible error.  MSN cites to caselaw suggesting that nothing stops the double patenting doctrine from applying even if Patent 2 (the ‘740 patent) was filed before Patent 1 (the ‘271 patent.).  MSN needs to win on this argument in order to prevail on its appeal.  Yet, whether MSN can win this argument is not a slam dunk.  The caselaw cited by MSN is not completely conclusive on the issue—i.e., there’s not necessarily binding precedent on this precise issue. 

Moreover, Acadia offers tractable arguments for why the district court’s reasoning was correct in this case.  In particular, the whole purpose of the double patenting doctrine is to prevent inventors from unfairly extending the life of a first patent with a second patent that is an obvious variation of the first patent.  But, according to Acadia, that did not happen in this case.  Indeed, the ‘740 patent did not extend the life of the ‘271 patent.  Rather, the ‘740 patent—which was the first patent to issue—set the original patent life for Acadia’s invention on pimavanserin.  

The ‘740 patent received additional patent life based on Patent Term Adjustment, whereas the ‘271 patent did not receive additional patent life.  But that, according to Acadia, is neither here nor there because Acadia did not exploit the patenting process to extend the life of the ‘740 patent.  Indeed, if double patenting did apply here, then the ‘271 patent would cut short the natural life of the ‘740 patent, which never would have happened if Acadia had never filed for the ‘271 patent in the first instance.  Acadia offers, not without reason, that that’s a bit backwards from the policy behind the double patenting doctrine.

Does the safe harbor provision apply?

Yet, even if MSN wins on its first argument, the district court also held that the safe harbor provision applied to prevent the ’271 patent (Patent 1) from acting as a double patenting reference for the ‘740 patent (Patent 2).  This, unfortunately, is where it gets really weedy and technical. 

For the safe harbor provision to apply, Patent 2 must be filed as a result of a restriction requirement issued during examination of Patent 1.  Technically, that did not happen in this case.   

The ‘271 patent (Patent 1) issued as a result of a follow-on patent application that was filed during examination of the ‘740 patent (Patent 2), but not in response to a restriction requirement.  Indeed, a restriction requirement was in fact filed during prosecution of the ‘740 patent, but not until after the follow-on application that led to the ‘271 patent was filed.  On its face, that should bar application of the safe harbor provision (i.e., favorable to MSN.)

On the other hand, the safe harbor statute technically says that the divisional application was filed “as a result of” the restriction requirement.  Acadia argues that that did happen in this case.  This is where it gets inconveniently technical, but the ‘271 patent issued from an application that was not filed as a divisional in response to a restriction requirement.  But the application was later amended to be deemed a divisional, and that amendment was made in response to the restriction requirement.  The district court found this was sufficient to be “as a result of” the restriction requirement.

This is a very specific legal question far out at the bounds of legal precedent.  Neither party really offers any dispositive caselaw on this point.  Indeed, the district court relied upon a 40-year old case that is technically not binding.  The Federal Circuit could technically go either way on this issue—if it reaches it—but, on balance, the limited caselaw that is available favors Acadia. 

MSN makes a final argument that the safe harbor provision should not apply because the ‘271 patent was not technically filed until after the ‘740 patent issued.  The arguments made by both parties drill down into the statutory text of the safe harbor provision, which is itself a heads-pinning provision.  (Read it for yourself: See 35 U.S.C. § 311).  Again, neither party has dispositive caselaw on its side.   

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This case is highly technical from a legal perspective.  Although the appellate briefs have all been filed, the oral argument has yet to be scheduled.  Listening to the oral argument, as well as the questions posed by the Federal Circuit panel, should offer more transparency into MSN’s chances of prevailing on this appeal.