The U.S. Food and Drug Administration said Tuesday that it had directed Amgen Inc. to stop pediatric studies of one of its drugs after 14-year-old patient died.

The FDA said it doesn’t know yet whether Sensipar – which treats a condition that can cause brittle bones, abdominal pain and kidney stones – was a factor in the teen’s death, but wanted the clinical trials stopped until that could be determined.

Sensipar, which earned FDA approval for adult use in 2007, is approved to reduce over-activity of the parathyroid gland as a result of chronic kidney disease and parathyroid cancer. Amgen reported sales of $950 million for the drug last year. Side effects of the drug itself can include calcium loss, nausea, vomiting and diarrhea.

The Thousand Oaks biotech was conducting three Sensipar studies in patients ranging in age from about 1 month old to 18 years. The patients had chronic kidney disease and secondary hyperparathyroidism and were receiving dialysis.

“Amgen is working as rapidly as possible to understand the circumstances of what happened,” Amgen spokeswoman Ashleigh Koss said in a statement.

Amgen shares closed down 8 cents, or less than 1 percent, to $89.47 on the Nasdaq.