Amgen, the giant biotech company based in Thousand Oaks, saw its shares drop 2 percent to $149.23 on Sept. 3 after its rival Novartis launched a drug similar to Amgen’s that costs 15 percent less.

Novartis’ Zarxio and Amgen’s Neupogen both help chemotherapy patients battle infections by increasing the production of white blood cells.

The Switzerland-based pharmaceutical company Novartis launched its drug today. It is priced at $275.66 while Amgen’s costs $324.60.

The U.S. Food and Drug Administration approved Zarxio in March but Amgen sued, stalling its debut. An appeals court ruled in July that Novartis could begin selling the drug on Sept. 2. Amgen’s temporary injunction was removed Sept. 3.

Zarxio is a part of a group of drugs called biosimilars. Biosimilars are like generics but they aren’t identical to the complex compounds they replicate and are made with living organisms. They threaten the multi-billion dollar sales of drugs made by other companies such as Chicago-based Abbvie and New Jersey-based Johnson and Johnson.

Novartis is also developing biosimilars for Amgen’s Enbrel, among others, according to a Barclays analyst.