As I have mentioned in the past, for an invention to be patentable, it must be both novel and inventive; the invention must be new and have some technical feature that renders it non-obvious over existing technology. In the chemical field, a new compound that is structurally different from any existing compound is usually sufficient to obtain patent protection. Once that compound has been patented, you could be forgiven for thinking that no further development on the compound is warranted. However, there are several strategies that can warrant further research and development on compounds that have been already been disclosed and/or patented.

As a result of the expense of developing new and innovative medicines, pharmaceutical companies often attempt to patent improved forms of the original medicine. The discovery of new crystalline forms of existing drugs, known as polymorphs, is one such area of research in which companies attempt to gain additional patent protection on existing drugs. Crystalline polymorphs may possess significant benefits, such as improved efficacy or lower toxicity, over the original compound. Usually, the specific crystalline form and the associated benefits cannot be predicted in advance and require research and development. For example, polymorphs of the antibiotic clarithromycin were successfully patented on the basis that the new forms possessed higher thermodynamic stability and higher solubility. Ultimately, the patentability analysis is the same — is the subject matter novel and inventive? In the case of the polymorphs of clarithromycin, the particular crystal structure was novel as it had not been discovered before and the associated stability and solubility properties provided the inventive aspect over the original drug. Courts in both Canada and the United States have confirmed that polymorphs of existing drugs constitute patentable subject matter. Patenting new crystalline forms provides a 20-year term of patent protection for the specific polymorph. However, the new patent would not prevent someone from selling the original form of the drug if that particular patent had expired.  

Another strategy for lengthening patent protection involves the discovery and selection of compounds within a broad genus that has already been disclosed. If you’ve ever reviewed a chemical patent for a compound or polymer, you’ll know that patent is drafted broadly and generically discloses millions of different compounds, which are described by using the generalized chemical symbols known as Markush structures. Obviously, the inventors of the original patent did not synthesize all of the disclosed compounds. If compounds or polymers are subsequently discovered that fall within the original Markush structure and which have an advantageous property over the initial disclosure, patent protection can be obtained for those compounds that have already been “disclosed.” It’s important to note that any subsequent compounds must not have been explicitly disclosed in the prior patent, even if the advantage had not been recognized. The second best-selling drug of all time, the blood-thinning medication Plavix, was the subject of a selection patent, the validity of which was confirmed by the Supreme Court of Canada (SCC) in 2008. While a somewhat unusual case, the SCC confirmed that the selection of one enantiomer from a known racemate, with the disclosure that the selected enantiomer had better activity, constituted a valid selection. The Plavix patent was filed in 1988 at a time when the selection and isolation of enantiomers were still relatively new. Today it’s unlikely that the selection of one enantiomer from a known racemate would result in patent protection as it is well known that different stereoisomers can have much different activity.

Finally, old compounds or polymers can be put to new use, and if that new use is not obvious, then patent protection can be obtained. It is well known that Viagra was initially developed as a medication for certain forms of hypertension, when an interesting side effect was observed. Pfizer subsequently patented the use of sildenafil for the treatment of erectile dysfunction. When preparing a patent application, it can be important for chemical inventors to be cognizant of potential non-obvious uses of a new compound, which are not the focus of the initial patent. Such non-obvious uses could eventually be the subject of patent protection and provide an additional term of protection.  

Mike Fenwick is a patent lawyer with Bereskin and Parr LLP in Toronto and holds a master’s degree in organic chemistry.