SAN FRANCISCO, March 19 (Reuters) - A U.S. judge on Thursday denied Amgen Inc's bid for a preliminary injunction against Novartis AG's Sandoz unit over disputed biologic product filgrastim.

The ruling, from U.S. District Judge Richard Seeborg in San Francisco federal court, involves Amgen's Neupogen drug, which is used to reduce infection rates in chemotherapy patients and generated $1.2 billion in sales worldwide in 2014.

(Reporting by Dan Levine; Editing by Chizu Nomiyama)