Amgen said it will buy privately held KAI Pharmaceuticals for $315 million to gain access to an experimental treatment for a common complication suffered by chronic kidney disease patients.

KAI's lead product, KAI-4169, is being tested as a treatment for a condition known as secondary hyperparathyroidism (SHPT), which is suffered by patients with chronic kidney disease who are on dialysis.

In connection with the agreement, Amgen has provided a loan to enable Phase III clinical development planning for KAI-4169 prior to closing. Through the acquisition, Amgen gains global rights to the drug, excluding Japan.

The deal has been approved by KAI shareholders and Amgen's board of directors, Amgen said.

In Phase II trials, KAI-4169 demonstrated a statistically significant improvement compared with a placebo with no discontinuations due to adverse side affects.

The drug is administered intravenously while a patient is undergoing dialysis, making patient compliance easier than having to remember to take pills. The vast majority of chronic kidney disease patients who need dialysis are affected by SHPT, which tends to worsen as kidney function declines, Amgen said.

There are about 1.6 million patients in the potential patient population in developed countries, the company said.

KAI-4169 is similar to Amgen's oral kidney drug Sensipar. ISI Group analyst Mark Schoenebaum pointed out in a research note that the KAI acquisition would give Amgen a branded drug in the category after patent protection runs out on Sensipar in 2015 in Europe and 2018 in the United States.