To determine the safety and efficacy of switch effects to adalimumab in etanercept-treated AS patients.

This single-centre, open-labeled randomized controlled study will evaluate the safety and efficacy of adalimumab in etanercept-treated Ankylosing Spondylitis(AS) patients.

Thirty patients will be enrolled and randomized equally into two arms.

Dosage and Administration：For standard dose(etanercept 50 mg weekly) treated patients, the treatment arm will receive adalimumab 40 mg subcutaneously biweekly for 8 weeks. The control arm will continue etanercept 25 mg subcutaneously twice a week for 8 weeks. At week 8, the control arm will be switched to adalimumab 40 mg subcutaneously biweekly for another 8 weeks.For half dose(etanercept 25 mg weekly) treated patients, the treatment arm will receive adalimumab 40 mg subcutaneously monthly for 8 weeks. The control arm will continue etanercept 25 mg subcutaneously weekly for 8 weeks. At week 8, the control arm will be switched to adalimumab 40 mg subcutaneously monthly for another 8 weeks.

Inclusion Criteria:

• Diagnosis of AS, as defined by 1984 Modified New York Criteria for AS.
• Stable background therapy as non-steroid anti-inflammatory for 2 weeks.
• Stable glucocorticoid for 4 weeks.
• Stable disease-modifying anti-rheumatic drugs, eg. sulphasalazine, methotrexate for 8 weeks.
• Stable anti-TNF biologics for 4 weeks.
• Written informed consent.

Exclusion Criteria:

• Serum creatinine ≥3.0 mg/dl.
• GPT≥5 times the laboratory's upper limit of normal.
• Pregnant or breast-feeding women.