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a measure of healthcare cost containment, the total number of vials of entanercept (25 mg) that can be prescribed for patients with inflammatory arthritis is restricted in Korea. Consequently, attempts to extend the dosing interval while maintaining the efficacy have not been an uncommon clinical practice. The aim of this study was to determine if extended doing interval of etanercept can be effective in patients with ankylosing spondylitis (AS). We performed a retrospective analysis using medical records at a single tertiary hospital. One hundred and nine patients with AS and 79 patients with rheumatoid arthritis (RA) started on etanercept between November 2004 and November 2009 were indentified. Etanercept (25 mg) was started with twice-weekly dosing schedule. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), C-reactive protein (CRP), and etanercept dosing interval for AS patients at 0, 3, 9, 15, 21 months were reviewed. Dosing interval for RA patients was analyzed for comparison. In AS, mean dosing interval was 4.7 ± 2.1 days at 3 months and was increased to 12.1 ± 7.0 days at 21 months. Despite the progressive increase in the dosing interval, the mean BASDAI declined rapidly at 3 months, and continued to decrease over 21 months. Mean CRP declined after 3 months of therapy and remained low thereafter. In RA, mean dosing interval was 4.0 ± 1.2 days at 3 months and 5.1 ± 1.8 days at 21 months. In conclusion, in AS, extended dosing of etanercept can be effective without compromising clinical and laboratory markers of disease activity as measured by BASDAI and CRP, respectively. Tapering of etanercept was less accommodating in RA when compared to AS. [ABSTRACT FROM AUTHOR]