Pfizer Inc v. Ajanta Pharma Ltd

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Pfizer Inc. (Delaware) and Pfizer Limited (England)
  • Defendant: Ajanta Pharma Ltd. (India)
  • Plaintiff’s Counsel: Morris, Nichols, Arsht & Tunnell LLP
• Case Identification: 1:18-cv-00188, D. Del., 02/01/2018
• Venue Allegations: Venue is asserted on the basis that Defendant is a corporation organized under the laws of India and that, upon approval, its generic product will be marketed and distributed in Delaware.
• Core Dispute: Plaintiff alleges that Defendant’s filing of an Abbreviated New Drug Application (ANDA) for a generic version of the erectile dysfunction drug Viagra® constitutes an act of infringement of a patent claiming a method of using sildenafil citrate to treat erectile dysfunction.
• Technical Context: The technology concerns oral pharmaceutical treatments for male erectile dysfunction, a field with significant commercial value.
• Key Procedural History: The complaint notes that the patent-in-suit, U.S. Patent No. 6,469,012, has a significant history. The asserted claims (25 and 26) were confirmed as patentable by the USPTO during reexamination proceedings. Furthermore, in prior litigation against a different defendant, a U.S. District Court found these same claims to be valid, enforceable, and infringed.

Case Timeline

Date	Event
1993-06-09	'012 Patent Priority Date
2002-10-22	'012 Patent Issue Date
2010-11-02	'012 Patent Reexamination Certificate Issued
2011-XX-XX	Prior litigation (Pfizer Inc v. Teva Pharma USA Inc) finds claims 25 and 26 valid and infringed
2017-12-23	Ajanta sends ANDA Notice Letter to Pfizer
2018-02-01	Complaint Filing Date
2019-10-22	'012 Patent Original Expiration Date
2020-04-22	Viagra® Pediatric Exclusivity Expiration Date

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 6,469,012 - "Pyrazolopyrimidinones for the Treatment of Impotence"

• Patent Identification: U.S. Patent No. 6,469,012, "Pyrazolopyrimidinones for the Treatment of Impotence," issued October 22, 2002.

The Invention Explained

• Problem Addressed: The patent describes a lack of effective and convenient treatments for male impotence. At the time of invention, available therapies included direct injection of vasoactive substances into the penis, which could cause side effects like pain and fibrosis, or less effective topical patches. (’012 Patent, col. 1:22-39).
• The Patented Solution: The patent discloses the unexpected discovery that a class of compounds known as pyrazolopyrimidinones, which are potent inhibitors of cGMP-specific phosphodiesterase (cGMP PDE), are effective in treating erectile dysfunction when administered orally. (’012 Patent, col. 1:61-66). This selective enzyme inhibition elevates cGMP levels, which relaxes the corpus cavernosum tissue and facilitates penile erection. (’012 Patent, col. 5:36-42).
• Technical Importance: The invention provided a basis for the first widely adopted oral therapy for erectile dysfunction, a common condition previously treated primarily with invasive or less reliable methods. (’012 Patent, col. 1:22-29).

Key Claims at a Glance

• The complaint asserts independent claim 25 and dependent claim 26. (Compl. ¶14).
• Independent Claim 25 recites:
  • 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 compound selected from a Markush group of nine specific chemical structures, or a pharmaceutically acceptable salt or composition thereof.
• Dependent Claim 26 narrows the compound of Claim 25 to a single chemical entity, 5-[2-ethoxy-5-(4-methyl-1-piperazinylsulphonyl)-phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one (sildenafil).

III. The Accused Instrumentality

Product Identification

The accused instrumentality is Ajanta’s generic sildenafil citrate tablets in 25 mg, 50 mg, and 100 mg dosages, for which Ajanta filed ANDA No. 206401 with the FDA. (Compl. ¶8, 18).

Functionality and Market Context

• Ajanta’s ANDA seeks approval to market its tablets for the treatment of erectile dysfunction. (Compl. ¶18). This is an artificial act of infringement under 35 U.S.C. § 271(e)(2), which makes the submission of an ANDA for a patented drug an act of infringement to create federal court jurisdiction.
• Ajanta’s ANDA filing included a “Paragraph IV” certification, alleging that its proposed generic product “will not infringe any valid or enforceable claims” of the ’012 patent, thereby seeking to enter the market before the patent's expiration. (Compl. ¶19). The complaint characterizes Pfizer's Viagra® as a "revolutionary" treatment. (Compl. ¶2).

No probative visual evidence provided in complaint.

IV. Analysis of Infringement Allegations

The complaint alleges that Ajanta’s filing of its ANDA constitutes infringement of claims 25 and 26. A key allegation is that Ajanta’s "Factual and Legal Basis" document, submitted with its Paragraph IV certification, "does not contain a noninfringement argument with respect to the Asserted Claims." (Compl. ¶21). This suggests Ajanta’s challenge may focus exclusively on the patent's validity.

’012 Patent Infringement Allegations

Claim Element (from Independent Claim 25 and Dependent Claim 26)	Alleged Infringing Functionality	Complaint Citation	Patent Citation
A method of treating erectile dysfunction in a male human…	Defendant’s ANDA seeks approval for its generic sildenafil citrate tablets specifically for the "treatment of erectile dysfunction."	¶18	col. 10:25-30
…comprising orally administering…	Defendant’s product is formulated as oral tablets.	¶18	col. 6:61-64
…an effective amount of a compound… [namely] 5-[2-ethoxy-5-(4-methyl-1-piperazinylsulphonyl)-phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one…	Defendant’s ANDA product contains sildenafil citrate, the compound specified in claim 26.	¶18	col. 12:35-40

Identified Points of Contention

• Statutory Infringement: In this Hatch-Waxman context, infringement is not based on a technical mismatch but is a statutory act triggered by the ANDA submission itself. The core question is whether Ajanta's proposed product, if marketed, would infringe. Given that the drug, dosage form, and indication appear identical to the claimed method, the primary dispute will likely shift away from infringement.
• Validity Challenge: The central point of contention will likely be Ajanta's challenge to the validity of claims 25 and 26. A question for the court will be whether Ajanta can present evidence of anticipation or obviousness sufficient to overcome the patent’s presumption of validity, which has been reinforced by prior successful reexamination and litigation. (Compl. ¶14).

V. Key Claim Terms for Construction

In ANDA litigation involving a bioequivalent drug for an identical indication, extensive claim construction disputes are less common than in other patent cases. However, the scope of the claimed method remains fundamental to the validity analysis.

• The Term: "treating erectile dysfunction"
• Context and Importance: This term defines the purpose and scope of the claimed method. Its construction is critical to the obviousness analysis, as the court must determine what a person of ordinary skill in the art would have understood this method to entail in 1993. Practitioners may focus on this term because the heart of the case is whether applying a known compound to this specific treatment method was an inventive step.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The patent specification broadly defines impotence as "an inability to obtain or sustain an erection adequate for intercourse." (’012 Patent, col. 1:11-14). This language could support a construction covering any condition meeting this functional definition, regardless of its underlying cause.
  • Evidence for a Narrower Interpretation: The background section notes that a majority of impotent males suffer from problems of "organic rather than of psychogenic origin." (’012 Patent, col. 1:20-21). A party challenging the patent might argue this context limits the scope of "treating erectile dysfunction" to only organically-caused conditions, potentially making the claim more susceptible to an obviousness challenge based on prior art related to physiological mechanisms.

VI. Other Allegations

• Indirect Infringement: The complaint alleges that upon approval, Ajanta will actively induce infringement by providing a product label that instructs physicians and patients to use the generic tablets in the patented manner. (Compl. ¶27). It further alleges contributory infringement, stating the tablets are especially adapted for this infringing use and have no substantial non-infringing use. (Compl. ¶28).
• Willful Infringement: The complaint alleges that Ajanta knew of the ’012 patent when it filed its ANDA. (Compl. ¶25). Plaintiff also requests a judgment that the case is "exceptional" under 35 U.S.C. § 285, which is the statutory basis for awarding enhanced damages and attorneys' fees, often predicated on a finding of willful infringement. (Compl., Prayer for Relief D).

VII. Analyst’s Conclusion: Key Questions for the Case

The dispute appears to be a classic Hatch-Waxman challenge, where infringement is straightforward and the case hinges on validity.

• A central question for the court will be one of patentability: was the claimed method of using sildenafil to orally treat erectile dysfunction obvious to a person of ordinary skill in the art as of the 1993 priority date, particularly in light of prior art disclosing the compound's cGMP PDE-inhibiting properties for cardiovascular conditions?
• A key evidentiary and procedural question will be the weight accorded to the patent’s history: can Ajanta’s validity challenge succeed in overcoming the high deference given to a patent that has not only survived USPTO reexamination but has also been previously adjudicated as valid and infringed in a separate federal court action?