Abstract Background/Aims Certolizumab pegol (CZP), a PEGylated TNFi without an Fc region, has previously shown efficacy and safety in patients with axial spondyloarthritis (axSpA). EULAR guidelines recommend that tapering of a biologic can be considered for patients in sustained remission. The C-OPTIMISE trial (NCT02505542) identified early (<5 years) axSpA patients in sustained remission who may benefit from dose tapering or stopping treatment. Here we report whether a reduced CZP maintenance dose is associated with sustained improvements in patient reported outcomes (PROs) in patients with axSpA at Week (Wk) 96. Methods C-OPTIMISE was a two-part, multicentre, phase 3b study in adult patients. Part A: up to Wk48 (open-label), patients received CZP 200mg Q2W. At Wk48 (Part B), patients who achieved sustained remission at Wk32 or 36 (ASDAS <1.3), were randomised 1:1:1 to double-blind CZP 200 mg Q2W (full maintenance dose), CZP 200 mg Q4W (reduced maintenance dose), or placebo (PBO [drug withdrawal]) for additional 48Wks. We report disease activity and PROs (BASDAI, PtGADA, nocturnal apinal pain, morning stiffness, fatigue, and ASQoL) during Part B (Wks48-96). Flare is defined as ASDAS ≥2.1 at two consecutive visits, or ASDAS >3.5 at any visit. Results At Wk48 (Part A), 43.9% (323/736) of patients achieved sustained remission, of which 313 patients were randomised to Part B (Wks48-96). During Wks48-96, 87/104 (83.7%) patients receiving the full maintenance dose, 83/105 (79.0%) patients receiving the reduced maintenance dose, and 21/104 (20.2%) patients receiving PBO remained flare-free. Patients receiving full maintenance and those on reduced dose have similar disease activity measures (BASDAI; mean [SD], 0.8 [0.8] vs 0.8 [1.0]) at Wk96 (Table). Sustained improvements in PROs were similar for CZP full maintenance dose and CZP reduced maintenance dose, including ASQoL, fatigue and nocturnal spinal pain, while PBO showed increased disease activity (Table). Conclusion In axSpA patients who achieved sustained remission, CZP reduced dosage resulted in sustained improvements in disease activity and PROs similar to those receiving full maintenance dose. This suggests that dose reduction can be a viable strategy without compromising PROs. Disclosure A. Chan: Member of speakers’ bureau; AC has received speaker bureau from Novartis, UCB, Abbvie, Janssen, Amgen. Grants/research support; AC has received grant support for service and educational projects from Novartis and UCB Pharma. Other; AC has received honoraria/advisory boards from Novartis, Abbvie, UCB, Janssen, Amgen, Lilly. J. Wood: Other; JW is an employee of UCB Pharma. L. Burns: Other; LBu is an employee of UCB Pharma. R. Tham: Other; RT is employed by Veramed and a contractor for UCB Pharma. T. Kumke: Other; TK is an employee and shareholder of UCB Pharma. B. Hoepken: Other; BH is an employee and shareholder of UCB Pharma. M. Kim: Other; MK is an employee of UCB Pharma. L. Bauer: Other; LBa is an employee and shareholder of UCB Pharma. K. MacKay: Other; KM received consultancy & speaker meetings for UCB, AbbVie, Novartis, Lilly, AZ, Janssen and Roche. K. Gaffney: Shareholder/stock ownership; KG is a shareholder of Rheumatology Events. Grants/research support; KG has received grants/research support from NASS, Versus Arthritis, AbbVie, Pfizer, UCB Pharma, Norvartis, Eli Lilly, Cellgene, Celltrion, Janssen, Gilead and Biogen. Other; KG has received honoraria/ consultation fees from Novartis, AbbVie, UCB Pharma, Lilly and Pfizer, KG has received speaker’s bureau from Novartis, UCB Pharma, AbbVie and Lilly; meeting expenses from AbbVie, Lilly, Roche, Novartis, Pfizer and UCB Pharma.