['Certolizumab pegol (CZP) is known to be effective as monotherapy at a dosage of 400 \u2009mg every 4 weeks in patients with active RA who have failed DMARDs. The aim of this study was to investigate every 4-week CZP in addition to continued MTX therapy in patients with an inadequate response to MTX alone.', 'Patients with active RA with inadequate response to MTX, on background MTX, were randomized to double-blind treatment with CZP 400 \u2009mg or placebo every 4 weeks for 24 weeks (NCT00544154). The primary efficacy end-point was the ACR 20% improvement criteria (ACR20) response rate at Week 24. Other end-points included ACR50 and ACR70 response rates, ACR core components, 28-joint DAS (ESR) with three variables (DAS28-3) and health-related quality-of-life outcomes in addition to safety.', 'Of 247 randomized patients, 126 received CZP and 121 received placebo, in addition to MTX. ACR20 response rates were 45.9 vs 22.9%, respectively [P\u2009<\u20090.001 analysed by the Cochran-Mantel-Haenszel (CMH) method], with improvements being apparent from Week 1. Statistically significant improvements over placebo were seen with CZP for ACR50, ACR core components, DAS28-3 and physical functioning. Rates of treatment-related adverse events were similar between groups (25.0 vs 27.7%), and there were no deaths or serious opportunistic infections.'] Is certolizumab pegol plus MTX administered every 4 weeks effective in patients with RA who are partial responders to MTX?