José Miguel Senabre-Gallego, Carlos Santos-Ramírez, Gregorio Santos-Soler, Esteban Salas-Heredia, Mabel Sánchez-Barrioluengo, Xavier Barber, José Rosas, On behalf of the AIRE-MB group

To date, anti-tumor necrosis factor alfa (anti-TNF-α) therapy is the only alternative to nonsteroidal anti-inflammatory drugs for the treatment of ankylosing spondylitis. Etanercept is a soluble TNF receptor, with a mode of action and pharmacokinetics different to those of antibodies and distinctive efficacy and safety. Etanercept has demonstrated efficacy in the treatment of ankylosing spondylitis, with or without radiographic sacroiliitis, and other manifestations of the disease, including peripheral arthritis, enthesitis, and psoriasis. Etanercept is not efficacious in inflammatory bowel disease, and its efficacy in the treatment of uveitis appears to be lower than that of other anti-TNF drugs. Studies of etanercept confirmed regression of bone edema on magnetic resonance imaging of the spine and sacroiliac joint, but failed to reduce radiographic progression, as do the other anti-TNF drugs. It seems that a proportion of patients remain in disease remission when the etanercept dose is reduced or administration intervals are extended. Etanercept is generally well tolerated with an acceptable safety profile in the treatment of ankylosing spondylitis. The most common adverse effect of etanercept treatment is injection site reactions, which are generally self-limiting. Reactivation of tuberculosis, reactivation of hepatitis B virus infection, congestive heart failure, demyelinating neurologic disorders, hematologic disorders like aplastic anemia and pancytopenia, vasculitis, immunogenicity, and exacerbation or induction of psoriasis are class effects of all the anti-TNF drugs, and have been seen in patients with ankylosing spondylitis. However, etanercept is less likely to induce reactivation of tuberculosis than the other anti-TNF drugs and it has been suggested that etanercept might be less immunogenic, especially in ankylosing spondylitis. Acute uveitis, Crohn's disease, and sarcoidosis are other adverse events that have been rarely associated with etanercept therapy in patients with ankylosing spondylitis.