Construing portions of the Hatch-Waxman Act (H-W), the U.S. Court of Appeals for the Federal Circuit held that the patent term restoration provision encompasses alternative salt and ester forms of an approved drug product, but clarifying that the term restoration provision is limited to registered uses of the approved product. Pfizer Inc. v. Dr. Reddy’s Laboratories, Ltd., Case Nos. 03-1227, -1258 (Fed. Cir. Feb. 27, 2004) (Newman, J.).

Norvasc is marketed as an anti-hypertensive, anti-ischemic drug product having the active ingredient amlodipine and is claimed in U.S. Patent No. 4,572,909 (the `909 patent) assigned to Pfizer, Inc. (Pfizer). The `909 patent term was set to expire in 2003, but was extended under H-W Act for a period equal to that time consumed in gaining regulatory approval. The act balances this term extension benefit to patentees by exempting infringement of generic producers for acts required for regulatory approval and allows use of the patentee’s data to support approval of a generic counterpart.

Pfizer submitted clinical data on both besylate and maleate salts of amlodipine to gain regulatory approval but selected amlodipine besylate to market. Pfizer’s application for term extension identified only amlodipine besylate as the approved product. Dr. Reddy’s Laboratories, Ltd. (Dr. Reddy’s) filed for regulatory approval to market amlodipine maleate for the same uses as Norvasc and also submitted Pfizer’s clinical data. While acknowledging that amlodipine maleate is covered by the `909 claims, Dr. Reddy’s persuaded the district court that the patent term extension applies only to the besylate salt form as the registered product and form identified in Pfizer’s term extension request. Pfizer appealed, arguing that regulatory approval was for "amlodipine" and that amlodipine maleate is within the scope of the statute as a salt or ester of the active ingredient.

Construing the term "drug product" under the H-W Act, the Federal Circuit held that the statutory definition is met by both amlodipine and its salts. The term drug product is defined as "any salt or ester of the active ingredient," where an active ingredient means a molecule responsible for physiological or pharmacological action, excluding appended ester or salt portions. The Court further reasoned that the H-W Act foresaw and avoided circumvention of the patent term extension provision by changing the salt form of the active ingredient. The Court also held that while amlodipine maleate is eligible for patent term extension, the restoration provision of the act is limited to approved uses of the drug product. This provision, therefore, excludes other uses of a drug, but maintains protection for other forms of the approved product that are subject to the extension.

In a dissent that focused on the eligibility requirement that limits term extension to drug products subject to regulatory review prior to commercial marketing, Chief Judge Mayer concluded that amlodipine maleate did not meet this requirement and should be precluded from patent term extension.

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