Pfizer Inc. v. Purepac Pharmaceutical Co.

395 F. Supp. 2d 153, 2005 U.S. Dist. LEXIS 37857
CourtDistrict Court, D. New Jersey
DecidedAugust 25, 2005
DocketNo. MDL NO. 1384(JCL); No. CIV.A.00-293(JCL)
StatusPublished
Cited by1 cases

This text of 395 F. Supp. 2d 153 (Pfizer Inc. v. Purepac Pharmaceutical Co.) is published on Counsel Stack Legal Research, covering District Court, D. New Jersey primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Pfizer Inc. v. Purepac Pharmaceutical Co., 395 F. Supp. 2d 153, 2005 U.S. Dist. LEXIS 37857 (D.N.J. 2005).

Opinion

MEMORANDUM AND ORDER

LIFLAND, District Judge.

Plaintiffs Pfizer, Inc., Warner-Lambert Co., and Godecke Aktiengesellschaft (collectively, “Warner-Lambert”) brought suit against Defendants Purepac Pharmaceutical Co. and Faulding Inc. (collectively, “Purepac”) alleging infringement of U.S. Patent No. 6,054,482, entitled “LactamFree Amino Acids” (“ ’482 patent”).1 [155]*155Purepae moves for summary judgment of noninfringement. For the reasons set forth herein, Purepac’s motion will be denied.

BACKGROUND

Neurontin® is sold by Warner-Lambert as an aid in the treatment of epileptic seizures and other cerebral disorders. The active ingredient in Neurontin® is a chemical compound called gabapentin. The chemical makeup of gabapentin allows the molecule, under certain conditions, to undergo an internal chemical reaction that results in a new compound called “gaba-pentin lactam.” Gabapentin lactam, which is more than twenty-five times as toxic as gabapentin, actually causes rather than prevents seizures. Given the serious risks posed by gabapentin lactam, Warner-Lambert scientists sought to minimize its formation. They did so by way of a process ultimately disclosed in the ’482 patent.

A. Development of Neurontin

Warner-Lambert scientists discovered that a stable formulation of gabapentin required careful limiting in two areas. First, it was critically important to ensure that the gabapentin itself was relatively pure. Second, the nature and amount of other additives in a gabapentin formulation affected stability. The former is pertinent to this Motion.

When making a drug to market commercially, pharmaceutical companies generally prefer to use a “salt” of a drug in order to promote good stability and solubility, and to ensure that it is not irritating at the site of administration. A “salt” is formed as a result of the reaction between an acid and a base wherein a hydrogen ion from the acid is transferred to the base. Drugs that are “basic,” like gabapentin, form a salt with hydrochloric acid (HC1). Upon discovering that the hydrochloride salt of gabapentin turned to lactam more quickly than gabapentin itself, Warner-Lambert scientists turned their attention from using the hydrochloride salt to using “free” gabapentin.

Gabapentin hydrochloride salt can be converted back to the neutral form of ga-bapentin through a process called ion exchange. Ion exchange involves a solution of gabapentin hydrochloride in water being passed through a column of ion exchange resin prepared in the “basic” form. (Bartlett Decl. ¶ 15). The hydrochloric acid (HC1) stays on the column while the neutral form of gabapentin comes out the bottom. (Id.). Removal of HC1 from ga-bapentin hydrochloride salt via ion exchange is a very efficient process. In a sample that has been prepared from gaba-pentin hydrochloride by ion exchange, there is a one-to-one correspondence between the number of chloride ions and the number of gabapentin molecules that remain in the acidic form. (Bartlett Decl. ¶ IT).2

B. The %82 Patent

The ’482 patent includes eleven claims-three independent claims (1,3,7) and eight dependent claims. Every claim in the ’482 patent includes the limitation that gaba-pentin have “less than 20 ppm” of an anion of a mineral acid or that an anion of a mineral acid does “not exceed 20 ppm.” [156]*156An anion is a negatively charged ion. Mineral acids include nitric, sulfuric, and hydrochloric acids. An anion of hydrochloric acid, for example, is chloride.

Claims 1 through 6 of the ’482 patent are process claims. (’482 patent, col. 6,1. 55 to col. 8, 1. 28). Independent claim 1 concerns a process for making gabapentin. Claim 1 specifies that the gabapentin compound resulting from the process must contain “less than 20 ppm” of an anion of a mineral acid. (’482 patent, col. 6, 11. 56-67; col. 7, 11. 1-20). Claim 2 depends from claim 1 and, accordingly, includes the “less than 20 ppm” limitation. (Id. at col. 7, 11. 21-22). Claim 3, the next independent claim, concerns a process for making a pharmaceutical composition containing ga-bapentin. Claim 3 specifies that the anion of a mineral acid remaining in the gaba-pentin compound produced during the process must “not exceed 20 ppm.” (Id. at col. 7,11. 23-57; col. 8,11. 1-16). Claims 4, 5, and 6 depend from claim 3 and, therefore, include the “not exceed 20 ppm” limitation.

Claim 7 of the ’482 patent, the only independent product claim, covers a pharmaceutical composition containing gaba-pentin:

7. A stable and pure pharmaceutical composition in unit dry medicinal dosage form consisting essentially of:
(i) an active ingredient which is gaba-pentin in the free amino acid, crystalline anhydrous form containing less than 0.5% by weight of its corresponding lac-tam and less than 20 ppm of an anion of a mineral acid and
(ii) one or more pharmaceutically acceptable adjuvants that do not promote conversion of more than 0.2% by weight of the gabapentin to its corresponding lactam form when stored at 25 C and an atmospheric humidity of 50% for one year.

(Id. at col. 8, 11. 29-40 (emphasis added)). Claims 8-11 depend from claim 7 and, therefore, incorporate all the limitations of claim 7, including the “less than 20 ppm” limitation.

The written description of the ’482 patent states that “[t]he proportion of remaining hydrochloride admixtures should thereby not exceed 20 ppm. The same also applies to other mineral acids.” (Id. at col. 5,11. 27-29).

C. The %82 Patent Prosecution History

The Godeeke scientists applied for a German patent on their discovery in August 1989. They filed a corresponding United States patent application in August 1990. The grant of the ’482 patent, on April 25, 2000, came after a series of continuation United States patent applications and multiple reviews by the patent examiner.

None of the claims as originally filed included the “less than 20 ppm” or “not exceed 20 ppm” limitation. Claim 8 in the application became patent claim 1. Application claim 8 did not initially include the “less than 20 ppm” limitation. Only after the patent examiner rejected claim 8 as being unpatentable due to the prior art did Warner-Lambert insert the “less than 20 ppm” limitation into claim 8.

Application claim 10 became patent claim 3. Claim 10 initially specified that “the proportion of remaining mineral acid admixtures does not exceed 20 ppm.” The examiner rejected claim 10 as being unpat-entable due to prior art and for failing to satisfy the definiteness requirement for patentability. Among other things, the examiner believed that the language “the proportion of remaining mineral acid admixtures does not exceed 20 ppm” was ambiguous. Ultimately, Warner-Lambert [157]*157amended application claim 10 to state that “the proportion of remaining anion of a mineral acid does not exceed 20 ppm.”

Application claim 5 provided the foundation for patent claim 7. During prosecution, Warner-Lambert canceled claim 5 and replaced it with claim 21, and subsequently canceled claim 21 and replaced it with claim 24. Application claim 24 issued as patent claim 7. Pharmaceutical claim 5 referred to and incorporated compound claim 1.

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Related

In Re Gabapentin Patent Litigation
395 F. Supp. 2d 153 (D. New Jersey, 2005)

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Bluebook (online)
395 F. Supp. 2d 153, 2005 U.S. Dist. LEXIS 37857, Counsel Stack Legal Research, https://law.counselstack.com/opinion/pfizer-inc-v-purepac-pharmaceutical-co-njd-2005.