"It's one of those rarer forms of arthritis, but when you anecdotally talk to some of the patients who have lived with the disease for some time, it really has an impact on their lives," said Rebecca Hamm, spokeswoman for Thousand Oaks, Calif.-based Amgen.
AS afflicts about 350,000 people in the U.S., typically striking between the ages of 16 and 30, and more commonly in men than women. Of those, Hamm said, Amgen believes about 100,000 would be eligible for therapy with Enbrel.
AS most often occurs in the lower back but may also affect the upper spine, chest and neck. In some cases the spine fuses partly or fully, causing loss of motion and a permanent stooped-over posture.
Patients now are "being treated with pain relievers, basically," Hamm told BioWorld Today. "We were able to show in Phase III [trials] that, for the first time, patients are seeing some improvements in the flexibility in their spines."
This marks the fourth approved indication for Enbrel, an anti-tumor necrosis factor drug first given the regulatory go-ahead in late 1998 as a treatment for rheumatoid arthritis. In June, an FDA panel unanimously recommended Enbrel's approval for AS. (See BioWorld Today, Nov. 3, 1998, and June 25, 2003.)
Enbrel's first approval was specifically for moderately to severely active rheumatoid arthritis in patients who had an inadequate response to one or more disease-modifying anti-rheumatic drugs. Since Amgen acquired the drug through its merger with Seattle-based Immunex Corp., Enbrel has been approved for juvenile RA, active arthritis in psoriatic arthritis patients and psoriatic arthritis. Earlier this month, Amgen filed for approval of Enbrel against psoriasis. (See BioWorld Today, July 9, 2003.)
Other TNF blockers under development in psoriasis are Remicade (infliximab), made by Centocor Inc., of Malvern, Pa., and Humira (adalimumab), the RA product from Abbott Laboratories Inc., of Abbott Park, Ill.
Remicade is already an overseas player in AS. Schering-Plough Corp., of Kenilworth, N.J., markets the drug for that indication outside the U.S., except in Japan and parts of the Far East. Wyeth, of Madison, N.J., is responsible for development of Enbrel outside of North America.
Remicade also is being developed in the U.S. for AS and other indications such as psoriasis and ulcerative colitis. In the RA field, Amgen's Enbrel faces increasing competition from Humira, approved in January for that indication and being explored as a treatment for juvenile RA, psoriatic arthritis, AS and psoriasis. Friday's no-surprise approval of Enbrel for AS is expected to help offset the RA inroads being made by Humira.
"We look at [AS] as a completely separate market" from RA, Hamm said, acknowledging that rheumatologists prescribe drugs as they find appropriate.
Amgen has forecast Enbrel sales to range between $1.2 billion and $1.4 billion in 2003, and Eric Schmidt, analyst with SG Cowen Securities Corp. in New York, predicted sales will exceed $3 billion by 2007. (See BioWorld Today, Dec. 18, 2001.)
Amgen's stock (NASDAQ:AMGN) closed Friday at $68.71, up 41 cents.