Under Korean law, the scope of a patent during the patent term extension (PTE) period is restricted to covering the "specific use" of the original approved product on which the PTE is based,^[1] unlike some foreign jurisdictions where the patent scope during PTE covers all types of use. However, the exact meaning of "specific use" has been the subject of much litigation in Korea in recent years.

The Supreme Court clarified several years ago in the Vesicare® decision that the scope of the PTE for the compound patent covering Astellas' Vesicare® product (main ingredient: solifenacin succinate) still covered generic products containing a different solifenacin salt (fumarate), which closed off one strategy used by Korean generic companies to try to enter the market before the expiration of PTE for compound patents by using salt forms different from the specific approved product. Since then, generics have tried using a different strategy for early entry by arguing that the scope of PTE is limited to the specific indications initially approved for the original product, as the meaning of the "specific use" of the original product, and then seeking approval only for subsequently approved indications for their products.

For example, about 70 local generic companies filed a record 213 scope confirmation actions against a single patent, the compound patent covering K-CAB Tab. (tegoprazan), arguing that the scope of the PTE for this patent was limited to the specific indications that were initially approved for the product (and excluding indications that were subsequently added to the approval). However, the Korean Intellectual Property Trial and Appeal Board (IPTAB) recently rendered decisions in all 213 cases, affirming that the PTE in this case still covered indications that were subsequently added to the approval.

The patentee filed a PTE application for the tegoprazan compound patent based on the initially approved indications (i) erosive gastroesophageal reflux disease and (ii) non-erosive gastroesophageal reflux disease. The additional indications (iii) gastric ulcer, (iv) antibiotic combination therapy for eradication of helicobacter pylori in patients with peptic ulcers and/or chronic atrophic gastritis, and (v) maintenance therapy after treatment of erosive gastroesophageal reflux disease were subsequently approved as well.

The generic companies argued that "specific use" under the Korean Patent Act meant the specific indications included in the original approval, and therefore the scope of the patent during PTE did not cover the subsequently approved indications. However, the IPTAB ruled in favor of the patentee that "use" referred to the therapeutic effect of the approved product, not merely the "indications" of the product, and that the scope of the compound PTE therefore continued to cover generic products used for subsequently approved indications in addition to the original indications.
 
The IPTAB's detailed reasoning was as follows: 

• Article 95 of the KPA stipulates that during the PTE period, the scope of the patent is limited to "acts of practicing the patented invention" related to the product whose approval was the basis for the term extension, though including the "specific uses" for which the product was approved. In other words, the statute limits PTE scope to practice of the patented invention, not the specific approved "product" (as determined by the Supreme Court decision in January 2019 in the Vesicare® case). Therefore, PTE scope is not limited only to "indications" which are specific to the product, but should be determined based on whether the therapeutic effect or use is substantially identical to the approved product underlying the PTE.
• According to the specification of the patented invention, the technical significance of the invention was in the creation of a novel tegoprazan compound that can be used for "acid-related diseases treated by inhibiting gastric acid secretion." Both the initially approved indications and the subsequently approved indications involved using tegoprazan to inhibit gastric acid secretion in the treatment of acid-related diseases.
• In view of (a) literature such as textbooks, guidelines, and academic publications, (b) the approval details of other medications belonging to the P-CAB (Potassium-Competitive Acid Blocker) Class, like K-CAB, and (c) the developmental history and approval status of previous generations of acid secretion inhibitors, it is clear that the initial and subsequent approved indications are substantially identical insofar as involving treating "acid-related diseases through the inhibition of gastric acid secretion."
• The argument that PTE scope only covers the initial approved indications, despite the initial and subsequent indications having substantially identical therapeutic effects or uses, is contrary to the purpose of the PTE system and the proper interpretation of Article 95 of the KPA. It should be noted that the initial approved indication is determined based simply on which clinical trial data happens to be available and submitted first.

These IPTAB decisions should have significant impact by affirming that "specific use" in Article 95 of the KPA should not be narrowly limited to only the initially approved indications. The decisions make clear that innovator drug companies, who have invested considerable effort in new drug development, are entitled to protection against generic companies seeking to simply bypass PTE protection without any substantive contribution to drug development. Most of the affected generics have appealed these decisions to the IP High Court, and the K-CAB case is expected to be the first appeal to decide the issue of the meaning of "specific use" under Article 95 of the KPA, so innovator drug companies would be well-advised to monitor further developments in this case.

^[1]   Article 95 of the Korean Patent Act ("KPA")