Amgen Inc. on Tuesday said that it signed an agreement to buy privately-held drug maker KAI Pharmaceuticals for $315 million in cash. KAI is developing an experimental treatment for a painful symptom of chronic kidney disease.

The Thousand Oaks biotech giant said that San Francisco-based KAI’s late-stage drug, KAI-4169, is being studied for the treatment of secondary hyperparathyroidism, which can result in swollen joints and deformed or fractured bones in patients with kidney disease.

It is administered intravenously while a patient is undergoing kidney dialysis. If successful, the drug would complement Amgen’s oldest drug Epogen, which is injected to treat anemia related to kidney disease.

“We are excited about acquiring KAI, as well as the opportunity to potentially deliver a novel therapy for chronic kidney disease patients on dialysis suffering from secondary hyperparathyroidism,” said Dr. Sean E. Harper, Amgen’s executive vice president of research and development, in a statement.

The deal has been approved by the boards of both companies and the shareholders of KAI, but is subject to regulatory approval. KAI would become a wholly-owned subsidiary of Amgen. As part of the deal, Amgen had provided a loan to enable late-stage clinical development planning for KAI-4169.

Shares were down 72 cents, or 1 percent, to $66.31 in midday trading on the Nasdaq.