Last year, the Korean Supreme Court ruled in a case interpreting the scope of the compound patent covering Astellas' Vesicare® product (main ingredient: solifenacin succinate) during the patent term extension (PTE) period that the Vesicare PTE covered generic products using different salt forms of the active ingredient in Vesicare. The Korean Patent Court has now further refined the reasoning of Vesicare in a subsequent set of cases concerning the scope of the compound patent PTE covering Pfizer's Champix® product (main ingredient: varenicline tartrate), holding that the generics in these cases remained within the scope of the Champix PTE even though they claimed their products had different formulation properties compared to the Champix product, and/or that it was not easy to select the salt forms used in their products.   

Brief Summary of Vesicare Decision¹ 

The Supreme Court Vesicare decision was the first in Korea to interpret the statutory limitation of PTE scope to "executing the patented invention on the products on which approval, etc. is the basis for registration of the extension," and established a two-part test for determining whether an accused generic product should be considered within the scope of a compound patent during PTE covering an original approved product. First, it should be determined whether the therapeutic effect exhibited through the pharmacological mechanism of the active ingredient in the accused product is substantially the same as that of the original approved product. Second, it should be determined whether it would have been easy for a person skilled in the art to select the salt form used in the accused product.

Facts and Issues in the Champix Case

21 generic companies filed scope confirmation actions against the Champix patent seeking decisions that their products (which used oxalate, fumarate, benzenesulfonate and salicylate salts of varenicline, rather than the tartrate) did not fall within the scope of Pfizer's compound patent PTE.

Despite the Supreme Court's decision in the Vesicare case, the Champix generic companies argued that their products were still outside the scope of the Champix PTE, on the basis that 1) their salts of varenicline had different formulation properties compared to varenicline tartrate (e.g., stability, solubility, etc.) and therefore would cause their generic products not to have substantially the same therapeutic effects compared to the original approved product, and 2) it would have been difficult to select their generic salt forms instead of the approved tartrate form because they were not expressly disclosed in the compound patent at issue (unlike in the Vesicare case), their salt forms were in a different pharmaceutical category than the tartrate form, and/or that Pfizer's separate patent on the specific varenicline tartrate form suggests that other salts would not easily have been considered in place of the tartrate.  

Patent Court's Ruling and Implications

Applying the Supreme Court's Vesicare test, the Patent Court held that the generics' products were within the Champix PTE despite their use of alternative salt forms, for the following reasons. 

Regarding therapeutic effects, the Patent Court noted that there was no dispute that the generic products and Champix used the same active ingredient and had the same pharmacological action to produce the therapeutic effect. The Patent Court also noted that both Champix and the generic products had the same use, to aid the cessation of smoking. The Patent Court rejected the generics' arguments, noting that even if using different salts might involve different formulation properties (such as solubility, absorption, stability, etc.) that may result in some change to therapeutic effects, in this case, the therapeutic effects of the generic products were still substantially the same as Champix given that the generic products relied on Champix clinical data for approval, and were approved simply on a showing of bioequivalence to Champix.

Regarding the ease of selection of the generic salt forms, the Patent Court rejected the generics' various arguments largely on the basis that because the approval documents of the generic products considered these salts to be commonly used salts for drug products. The Patent Court noted that no generic products were designated as "modified new drugs" which would have indicated they were improved compared to the original drug product or possibly inventive. The Patent Court also rejected the salt classification argument as irrelevant, given that all of the salt forms at issue were considered commonly used pharmaceutical salts. Finally, the Patent Court rejected the generics' argument that that Pfizer's separate patent on the tartrate taught away from other salt forms, noting that the separate patent merely disclosed the advantageous formulation properties of varenicline tartrate in general terms, and did not compare the tartrate form with the salt forms used in the generic products.

The Patent Court's Champix decision usefully clarifies the Supreme Court's decision in the Vesicare case, by indicating that any accused product that is approved based only on bioequivalence to the original approved product will likely within the scope of a PTE covering the original approved product regardless of whether it uses a different salt form of the active ingredient.