Pfizer won a patent lawsuit against local drugmakers over its antismoking drug Champix on Friday.

With the ruling, the domestic manufacturers will find it almost impossible to roll out their generic copies by changing the base of the drug to avoid Pfizer’s substance patent.

The Intellectual Property Trial and Appeal Board (IPTAB) ruled that it would reverse its earlier decision on 20 Korean companies, which had ruled that they did not infringe on the patent of Champix.

In September 2016, more than 20 local drugmakers requested the court to validate their passive rights to the Champix patent. Their move aimed to avoid the Champix substance patent, which expires on July 19, 2020, through changing the base of the drug.

In April 2018, IPTAB ruled in favor of the local companies, saying they did not infringe on the patent of Champix concerning the extension of the medicine's patent duration.

However, the patent court reversed the decision on Friday.

The domestic companies participating in the suit include Hanmi Pharmaceutical, Kolmar Korea, KyungDong Pharm, Ildong Pharmaceutical, Hanhwa Pharma, Korea Prime Pharm, For New Farm, Unimed Pharm and Yuyu Pharma.

The court also rejected Hanmi Pharmaceutical’s appeal filed in June to invalidate the Champix patent.

In response to the latest ruling, Pfizer Korea General Manager Oh Dong-wook said, “The law should adequately protect the patent right of a drug. We welcome the reasonable judgment of the patent court in line with the aim of extending the patent right period.”

With the ruling, domestic and foreign pharmaceutical companies' rights to innovative medicines will be respected and their value, recognized, which will advance the pharmaceutical industry further, he added.