Understanding "Prior Art"


"Prior art" is the mass of pre-existing knowledge that an invention must distinguish over to qualify for a patent. Distinguishing over "prior art" often leads to creative ways to express or define an invention, but the threshold question is: What actually constitutes prior art?

Prior art has been generically defined as "technology already available to the public," but a better definition is anything that can be cited against a patent (or patent application) to challenge the novelty or "nonobviousness" of the invention. The most common forms of prior art are other patents, published literature, and information generally known or accessible to those knowledgeable in the field in which the invention resides. Prior art also includes knowledge that is not public or publicly accessible, such as commercial operations and offers for sale of what is later claimed as the subject matter of an invention, even if the particulars of the commercial operation are maintained as a trade secret or the offer is made on a confidential basis. Prior art commercial operations and offers for sale are more limited in scope than publication-type prior art: commercial operations and offers for sale must take place within the United States to qualify as prior art. Nevertheless, commercial operations and offers will qualify as prior art even if neither the public at large nor anyone in the relevant industry has actual knowledge of their occurrence or the ability to obtain such knowledge.

A third type of prior art is one that is even more difficult to detect––the simple "making" of an invention in the United States by an earlier inventor before the later inventor (who applies for a patent) conceives of the invention. This "making" is prior art even if the one doing the "making" never applies for a patent and neither publishes the invention, uses it commercially in the United States, or offers the subject of the invention for sale in the United States. The prior "making" of an invention can thus constitute prior art even if neither the later inventor, the industry, nor the scientific community in general has any way of knowing that this "making" occurred either at the time that it did occur or at any time before the later inventor applied for a patent. Since it is so obscure, however, this prior "making" of an invention has a special limitation: it will qualify as prior art only if has not been "abandoned, suppressed, or concealed." How does one show that a prior making of an invention has not been abandoned, suppressed, or concealed?

These questions came up in a patent infringement lawsuit, recently affirmed on appeal, relating to enalapril maleate, a pharmaceutical compound used in the treatment of high blood pressure. A known problem with this drug was its instability in the presence of the excipients needed for formulating the drug as a tablet. Stability could be improved by converting the enalapril maleate to enalapril sodium salt, but this required suspending the enalapril maleate in water, adding an alkaline sodium compound, and mixing the suspension until the acid-base reaction was complete. This was both time-consuming and detrimental to product quality since it caused hydrolysis of the active ingredient. The initial patents on the drug itself were owned by Merck and Co. Several years after the Merck patents were granted, Merck's competitor Apotex Corporation obtained U.S. patent coverage for a quicker and safer process for converting the maleate to the sodium salt: dry blending the components, adding only enough water to moisten the blend, then simply drying the moistened blend. Upon discovering that Merck was using the process, Apotex sued for patent infringement.

Among the defenses that Merck raised was a prior art defense, claiming that Merck itself had discovered and tested the process at its laboratory in West Point, Pennsylvania, well before Apotex had conceived of the process. Despite the successful test, Merck did not itself apply for a patent on the process, and the only commercial operations in which it used the process were outside the United States. As its defense, Merck claimed that its laboratory tests were a prior "making" of the invention in the United States and therefore prior art against Apotex, and the court agreed. The next step was to determine whether Merck had abandoned, suppressed, or concealed this knowledge. Apotex responded by stating that after Merck had performed the testing, five years passed before Merck took any steps to make the information accessible to the public. This was sufficient to raise an inference of suppression or concealment. Merck acknowledged the delay but maintained that the delay ended when various disclosures were made by that Merck before Apotex' invention date. The court agreed, and Apotex' patents was declared invalid over the prior art. Thus, while the challenger must show that a prior "making" of an invention was not abandoned, suppressed or concealed, this form of "prior art" is particularly difficult for inventors to find on their own.