Amgen agreed to buy KAI in April. The South San Francisco, Calif., company is developing an experimental treatment for secondary hyperparathyroidism in patients with chronic kidney disease who are on dialysis.

The parathyroid glands release a hormone that helps control the amount of calcium in a person’s blood. When the glands are not working properly, levels of calcium and phosphorous can get too high. Amgen said patients with kidney disease often develop parathyroidism, and the condition can get worse as their kidney function declines.

The deal calls for Amgen to make a loan to KAI so it can plan late stage trials of the hyperparathyroidism drug, which is designated KAI-4169.

Shares of Amgen slipped 83 cents to end Thursday’s regular session at $74.33. The stock gained 10 cents in aftermarket trading.