Domestic pharmaceutical companies have been competing to develop generic copies of Azilect (ingredient: rasagiline mesylate), the original treatment for Parkinson’s disease released by Lundbeck Korea in 2014.

According to the Ministry of Food and Drug Safety, 13 drugmakers have won the approval for an equivalence test on their generic imitations of Azilect as of Monday.

In April, Yuyu Pharma, Myungin Pharm, Chong Kun Dang, Hyundai Pharmaceutical, Mother’s Pharm, Jeil Pharmaceutical, Samil Pharmaceutical, Korea Pharma, BC World Pharm, Hwanin Pharmaceutical, C-TRI, and Kolmar Korea won the green light. On Monday, Myungmoon Pharm followed suit.

Including Kyungbo Pharm, which is working on a generic with a different base, 14 pharmaceuticals are preparing to compete in the Azilect market.

Rolled out in Korea in 2014, Azilect has posted steady growth in prescriptions for the past four years. Last year, the original drug sold 8.5 billion won ($7.5 million). The market leader Mirapex recorded 9.2 billion won in sales, followed by Stalevo with 9.1 billion won, and Requip with 5.9 billion won.

Azilect’s robust sales growth is attributed to its strength in the continuous period of efficacy even in long-term use. Other conventional medicines had the time of efficacy shortened in long-term use.

Azilect’s use patent expired on May 22, 2016. However, its patent on the crystal form of rasagiline mesylate is valid until Dec. 13, 2027.

To defend the Azilect market, Lundbeck obtained approval for Azilect 0.5 mg, half the dosage of the previous product Azilect 1 mg, in September.