Biotechnology company Amgen Inc. said Monday an ongoing study of its drug Enbrel showed patients with a spine inflammation condition had positive results, consistent with a previous late-stage study.

The drug was approved by the Food and Drug Administration in 2003 to treat ankylosing spondylitis, a chronic inflammation of the spine and joints at either side of the spine. The ongoing open study showed that after a period between 148 and 160 weeks, patients maintained improvement in spinal mobility. The condition is known for impeding movement and flexibility.

In all, 59 patients received the drug in the ongoing study, and 78 percent of them improved based on a clinical scale measuring back pain, physical function and inflammation. The drug appeared to be safe and tolerable in the long-term study.

The results from the ongoing study reflect those seen in late-stage clinical trials, in which patients improved over a 24-week period.

The drug was approved in 1998 to treat inflammation associated with rheumatoid arthritis.

Shares of Amgen fell 46 cents to $73 on the Nasdaq in morning trading.