I received a letter from a reader asking about the current status of the reexamination request on Pfizer’s Viagra (sildenafil citrate) patent (U.S. Pat. No. 6,469,012). I always appreciate hearing from readers and don’t mind trying to answer questions (when I can) so I reviewed the file history. The proceedings are now merged (consolidated into one) and the actions to date are summarized below.

In October 2002, Pfizer Inc., Pfizer Limited, and Pfizer Ireland Pharmaceuticals filed a patent infringement lawsuit against ICOS, Lilly ICOS, and Lilly in the United States District Court for the District of Delaware. Pfizer contends that the use, offering for sale, selling, manufacture, or importing into the United States of Cialis for the treatment of erectile dysfunction by any of the defendants infringes claim 24 of Pfizer’s U.S. Patent No. 6,469,012, and seeks a declaratory judgment to that effect. Pfizer also seeks a permanent injunction, attorneys’ fees, costs, and expenses.

The USPTO subsequently ordered the reexamination of the Pfizer Patent (Reexam. C.N. 90/007,478). Under the reexamination process, the PTO is required to reconsider the validity of a patent if substantial new questions of patentability are raised by any party including by the PTO itself. The District Court stayed, or suspended, the patent infringement lawsuit, pending the outcome of the reexamination. Subsequently, Lilly ICOS and other parties filed several reexamination requests regarding the Pfizer Patent, which were merged with the USPTO-ordered reexamination. The first office action issued by the PTO rejected claim 24 of the Pfizer Patent. Claim 24 reads:

A method of treating erectile dysfunction in a male human, comprising orally administering to a male human in need of such treatment an effective amount of a selective cGMP PDEv inhibitor, or a pharmaceutically acceptable salt thereof, of a pharmaceutical composition containing either entity.

The Examiner rejected claim 24 on the basis that certain prior art rendered the claimed invention not new, and therefore unpatentable under 35 U.S.C. §102(b), and obvious and unpatentable under the judicially created doctrine of obviousness-type double patenting. This broad claim would cover treatment by any cGMP PDEv inhibitor (read: Cialis) and was rejected over the references Korenmann, 41 J. Am Geriatrics Soc. 363 (1993) and Yin et al., 10(6) Yunnan J. Traditional Chinese Medicine 13 (1989).

On September 15, 2005, the USPTO issued a second office action that rejected Pfizer’s arguments made in response to the first office action, reaffirmed the initial rejection of claim 24, and entered new grounds for rejecting claim 24. The second office action also maintained the obviousness-type double patenting rejection of the other claims. Pfizer’s response to the second office action was due by November 15, 2005. The time for taking any action by a patent owner in an ex parte reexamination proceeding can be extended only for sufficient cause and for a reasonable time specified. Any request for such extension must be filed on or before the day on which action by the patent owner is due, but in no case will the mere filing of a request effect any extension.

Therefore, the time for response has passed but it is possible that Pfizer will file with an extension of time or that the response has just not made it to the file wrapper as yet. If a response has been filed, the USPTO could issue a further action, which may finalize the rejections of claim 24, withdraw the rejections of that claim, or allow an amended claim to be entered. In any event, Pfizer may challenge the result of a final office action within the PTO and subsequently in court.

ICOS and Lilly also have initiated or are defending lawsuits and/or administrative proceedings against Pfizer in other jurisdictions around the world regarding patents corresponding to Pfizer’s U.S. “method of use” patent. The corresponding patent in the UK was found invalid as obvious by the Court of Appeal in Lilly ICOS Ltd v. Pfizer Ltd. (2002) EWCA Civ 1 and Civ 2 and in Australia in Eli Lilly v. Pfizer (2005) FCA 67.

UPDATE: Dr. Vivien Santer, a patent attorney with Griffith Hack in Australia, sent a note pointing out that the case was litigated in Australia, and at first instance claim 10 was held by the Federal Court of Australia to be invalid for lack of inventive step and for lack of fair basis (analogous to lack of support in the specification under US Section 112). Claim 10 is the equivalent of US claim 24, and would have encompassed Cialis. However, the Full Federal Court held on appeal that the invention as claimed was novel and not obvious, but then it upheld the finding of invalidity of claim 10 on the ground of lack of fair basis. A case of winning the battle but losing the war. The appeal decision can be found here.

We’ll keep you posted on any further actions on this matter.

See the Nonfinal Office Action here.

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