A federal judge on Thursday denied Amgen Inc.’s bid to stop the sale of a biosimilar form of Neupogen, the company’s infection-fighting blockbuster drug for cancer patients.

The Thousand Oaks pharmaceutical company filed paperwork on Feb. 6 seeking a preliminary injunction to stop Novartis AG from selling Zarxio, a copycat version of Neupogen, one of Amgen’s best-selling drugs with revenue last year of about $1.16 billion.

Amgen attorneys argued Novartis hadn’t complied with the time elements specified in the law allowing biosimilars. Novartis attorneys filed counter arguments that Amgen’s lack of cooperation caused delays and the timing issues.

In his ruling, Judge Richard Seeborg of the U.S. District Court in San Francisco, denied Amgen's request for an injunction, clearing the way for Novartis to begin marketing Zarxio.

In a statement, Amgen said it was “disappointed in the district court’s decision” and will appeal the ruling.

Earlier this month, the Food and Drug Administration approved Zarxio, making it the first biosimilar to pass regulatory muster in the United States. Biosimilars are medicines that copy proprietary biotech drugs when patent protection expires. Because small differences in the environment or manufacturing processes may alter the final product, the drugs are called similar – but not identical – to the original drug.

The patent for Neupogen, which increases the number of infection-fighting white cells in the blood, expired last year. Neupogen is for cancer patients undergoing radiation or chemotherapy, which depletes white cells.

Amgen shares closed up $2.57, or 1.5 percent, to $169.11 on the Nasdaq.

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