Judy M. Mohr, PhD

Limitations on patent-term extension under the Act are neatly summarized by the "rule of ones:" one patent extension per product, one patent extension per patent, and one product per patent extension.¹ "One patent extension per product" refers to the statutory requirements that no other patent has been extended for the product,² and that "in no event shall more than one patent be extended for the same regulatory review period of any product."³ "One patent extension per patent" reflects the requirement that the term of the patent has never been extended."⁴ The third rule, "one product per patent extension," derives from the goal of the Act to allow a restoration of patent term only for the product for which regulatory approval was sought. That is, only the product that served as the basis of the extension is exclusively covered by the patent during its extended term.

These rules adequately address most, but not all, patent-term extension issues. This article addresses one of the "ambiguous" outcomes under the rules of one, and how the courts are currently dealing with this issue. The question raised is this: If marketing approval for a particular form of a drug is granted, and the term of patent covering that form of the drug is extended under the Act, is it possible to extend the term of a patent on a different form of the drug, e.g., a different salt or free-base, or free-acid form of the same drug?

This question was considered by the Court of Appeals for the Federal Circuit in Glaxo Operations UK Limited v. Quigg.⁵ Glaxo (now GlaxoSmithKline) sought a patent-term extension for cefuroxime axetil, which had been approved for marketing as a broad spectrum oral antibiotic under the trade name Ceftin. Cefuroxime sodium had been previously approved as an injectable antibiotic, marketed as both Zinacef and Kefurox. Glaxo's patent-term extension for cefuroxime axetil, an ester of cefuroxime, was denied by the US Patent and Trademark Office on the grounds that it was not the initial permitted commercial marketing or use of the product, a violation of the "one patent extension per product" rule. Glaxo argued that cefuroxime axetil is not the same "drug product" as cefuroxime sodium. The court agreed with Glaxo, reasoning that (a) the already approved drug was cefuroxime sodium; (b) a "drug product" under the Act means an "active ingredient of a new drug....including any salt or ester of the active ingredient" (35 U.S.C. § 156 (f)(2)); and (c) cefuroxime axetil is not a salt or ester of the cefuroxime sodium. In other words, cefuroxime axetil was not the same "active ingredient" as the cefuroxime sodium because it was not "a salt or ester" of cefuroxime sodium. This result is not illogical, because different drug forms could be considered to be different "drug products" based on differing pharmacokinetics and, sometimes, pharmacodynamics. That is, the two drugs might be considered to be different "active ingredients." The court's reasoning in Glaxo is not based on any demonstrated distinction between the two compounds at issue. Rather, it appears to rely on the misunderstanding that sodium salt of an active anionic compound cannot have an ester form. This reasoning would lead to diametrically opposed results, depending on whether the drug that was approved originally, was in a salt or acid form.