As part of the 1984 legislative package making it easier for manufacturers of generic drugs to obtain FDA approval to market these drugs, Congress provided for extensions of the terms of patents in some cases to enable the pharmaceutical industry to obtain an extension of the term of patents for new drugs to compensate for the time taken to obtain FDA approval before they could be marketed.

A single extension of the term of a patent may be obtained if the patent relates to the active ingredient of a human or animal drug product or a combination of such active ingredients, a medical device, a food additive or a color additive or to methods of manufacturing or using such products and the product is subject to regulation under the Food, Drug and Cosmetic Act. [227]

A patent relating to one of these regulated products is a candidate for an extension if the date of first marketing the product, or in the case of a process using recombinant DNA technology the first use of the process, was delayed as a result of regulatory review. Subject to a statutory maximum discussed below and subject to the applicant having been diligent in seeking regulatory approval, the extension shall be for the same period as marketing was delayed as a result of the regulatory review. [228]

The regulatory period is defined in different ways for the five different categories of product covered by this provision: (1) new drugs for human use, (2) new food or color additives, (3) new medical devices, (4) new animal drugs and (5) new veterinary biological products. The basis for the differences is that the approval procedures differ between these classes of products. By way of example, it may be noted that for new drugs for human use, the regulatory period is one half of the term starting on the date on which an investigational new drug exemption is granted, thereby permitting clinical testing in the United States, and ending on the date on which a request for marketing approval is filed plus the entire period during which the request for marketing approval is pending. [229] It may therefore be useful for those resident outside the United States to file an IND for a new drug earlier than might otherwise have been the case in order to maximize the benefits they may obtain from the law.

A petition for extension of the term of a patent must be filed within 60 days of the marketing approval being given and must be filed before the patent expires. [230]

Extensions of patents under the act are, however, subject to two types of limitation: a maximum duration of extension and a limitation on the scope of the patent during the extended period.

The limitations on the duration of the extension are twofold. First, the extension shall not result in the final expiration of the patent occurring more than 14 years after sale of the product is approved. [231] Second, the actual duration of the extension shall not exceed 5 years if the patent issued after the new law came into effect or no permitted clinical investigation prior to filing a formal request for approval of the new product was carried out before the new law came into effect. However, if the patent had issued before the new law came into effect and such preliminary testing had been carried out, but no approval for commercial marketing had been issued by that date, the maximum period of extension is two years. [232]

The scope of protection during the extension is limited to the product, which has been approved following the regulatory review, an approved use thereof or a method of manufacturing the approved product depending on the claims of the patent. [233] Thus, if one has three patents relating to drug X, one for the product per se and describing its use in the treatment of disease Y, a second for an improved means of producing drug X and a third for use of drug X in the treatment of disease Z, and one submits two applications to the FDA for approval of drug X, one for its treatment of disease Y and the other for its treatment of disease Z only two of the three patents may be extended, one for each of the two review periods.

Failure to disclose all relevant facts in a petition for an extension is a ground for invalidating the extension. [234]

A subsequent law relating to an extension of terms relating to animal drugs is modeled on the provisions that already exist for human drugs. As with human drugs provision is made for the filing of an Abbreviated New Drug Application with the Federal Food and Drug Administration to expedite the marketing of generic animals drugs once patent protection for them has expired. It is, however, expressly provided that the new provisions do not apply to any new animal drug "which is primarily manufactured using recombinant DNA, recombinant RNA, hybridoma technology or other processes involving site specific genetic manipulation techniques". [235]

The abbreviated procedure will not apply for a period of five years after first approval under "normal" FDA procedures for any active ingredient unless the application for the ANDA contains a certificate showing that no valid patent will be infringed in which case a four year delay period before the abbreviated procedure can be used shall apply. In cases where a second application for a particular compound has already been approved (for example, as a result of its being approved for a different use) a period of three years from the original approval of the new use will apply before an abbreviated new drug application will be approved.

The law also provides for release of certain safety and effectiveness data in connection with new animal drug applications to be made available to members of the public for certain limited purposes and also introduces limitations on the distribution of animal drugs by requiring that certain of them can be supplied only "upon the lawful or written or oral order of a licensed veterinarian in the course of veterinarian's professional practice."

Finally, the law provides for extension of the patent term in respect of patents relating to new animal drugs to compensate for the time taking in obtaining regulatory review and approval. These terms are calculated in essentially the same way as for human drugs and are subject to the same overall limitation that the maximum term of extension is five years.

The question of how to determine whether a patent was capable of extension came up in Hoechst-Roussel Pharmaceuticals v. Lehman. [236] Warner-Lambert had received FDA approval to market a drug for treatment of Alzheimer’s disease whose active ingredient is tacrine hydrochloride. Hoechst-Roussel sued Warner-Lambert for infringement of its patent claiming 1-hydroxytacrine and a method of treating a patient in need of memory enhancement by administering an effective amount of 1-hydroxytacrine. Tacrine hydrochloride, after ingestion, metabolizes into, inter alia, 1-hydroxytacrine. Warner-Lambert entered into a consent judgment in which it admitted that tacrine hydrochloride infringes certain claims of Hoechst-Roussel’s patent.

Hoechst-Roussel applied for an extension of the term of its patent under the provisions of the Patent Term Extension Act which provides for the availability of an extension of the term of a patent if the claimed product must undergo regulatory review before it can be marketed. The Commissioner of Patents and Trademarks denied the application on the basis that Hoechst-Roussel’s patent did not claim tacrine hydrochloride or the method of using tacrine hydrochloride.

Hoechst-Roussel appealed the decision to the Court of Appeals of the Federal Circuit and the decision of the lower court was affirmed. The Federal Circuit stated that the issue was whether the patent claimed the product that was subject to regulatory review, not whether the marketing of the product would infringe the claims of the patent.