CT-P13 is an infliximab biosimilar approved for indications including ankylosing spondylitis (AS); the approved maintenance regimen is 5 mg/kg infused every 6-8 weeks. In clinical practice, modifications to infliximab dose and/or infusion interval can be beneficial to the patient. For CT-P13, real-world data on dose and/or interval adjustment are lacking. This analysis investigated the impact of such treatment pattern changes on effectiveness and drug survival up to five years for adult (≥18 years old) patients with AS in the Korean, real-world, retrospective rheumatoid arthritis and ankylosing spondylitis (RAAS) study. Overall, 337 patients with AS were identified: 219 who initiated infliximab treatment with CT-P13 ('naïve') and 118 who switched from reference infliximab to CT-P13 ('switched'). Overall, 18/235 (7.7%), 110/224 (49.1%), and 101/186 (54.3%) evaluable patients had dose, infusion interval, or combined treatment pattern changes, respectively. More naïve (61.0%) versus switched (42.6%) patients had treatment pattern changes. Overall, Bath Ankylosing Spondylitis Disease Activity Index scores decreased from baseline to week 54, then remained stable; improvements were greater for patients with than without treatment pattern changes. Drug survival did not differ significantly between patients with or without treatment pattern changes. Findings suggest that adjusting dose and/or infusion interval can improve clinical outcomes for CT-P13-treated patients with AS.