Amgen Inc. has completed its $315 million acquisition of KAI Pharmaceuticals.

Privately held KAI becomes a wholly owned subsidiary of the Thousand Oaks biotech. The South San Francisco company is in late-stage clinical trials for a drug to treat chronic kidney disease patients who are on dialysis. The levels of calcium and phosphorous in the patients’ bodies can get too high and cause swollen joints and bone fractures.

The completion of the acquisition was announced late Thursday.

Amgen markets its own treatment for the condition, Sensipar, which had worldwide sales of $808 million last year. Both Sensipar, which is taken as a pill, and KAI’s experimental KAI-4169, which is injected, complement Amgen’s injectible Epogen, which treats anemia related to kidney disease.

The deal was announced in April.

Shares were down 39 cents, or less than 1 percent, to $73.94 in Friday midday trading on the Nasdaq.