The Food and Drug Administration on Tuesday approved a new drug called Omontys, which is poised to break Amgen Inc.’s near monopoly in the roughly $6 billion U.S. anemia treatment market.

Omontys, developed by Affymax Inc. of Palo Alto, was approved for use by adult dialysis patients with anemia caused by chronic kidney disease. There are about 400,000 U.S. kidney disease patients on dialysis.

Omontys is injected monthly, which gives it an advantage over Amgen’s anemia drug for chronic kidney disease, Epogen, which generally is administered three times a week. Epogen, approved in 1989, is the Thousand Oaks biotech’s oldest product and had sales of about $2 billion last year,

Omontys “offers patients and health care providers the convenience of receiving (anemia) therapy just once per month instead of more frequent injections,” said Dr. Richard Pazdur, director of the Office of Hematology and Oncology Products at the FDA’s Center for Drug Evaluation and Research, in a statement.

Amgen also supplies a version of Epogen to Johnson & Johnson that is sold under the name Procrit for use in nondialysis kidney patients and for chemotherapy-related anemia. And it sells a longer-lasting anemia drug called Aranesp.

Amgen shares earlier closed up 29 cents, or less than 1 percent, to $67.81 on the Nasdaq.