Objectives The aim was to compare continuous and on-demand NSAID treatment with respect to their ability to suppress radiographic progression in subgroups of patients with high/elevated CRP-levels, ESR, ASDAS-levels or BASDAI-levels in comparison to patients with normal levels.

Methods Post-hoc analyses were performed in a randomized trial comparing continuous and on-demand NSAID treatment. Relevant high/elevated subgroups were created based on time-averaged (ta) CRP (>5mg/L), ta-ESR (>12mm/hr), ta-BASDAI (>4), ta-ASDAS-CRP (>2.1) and ta-ASDAS-ESR (>2.1). Subgroups were further split according to NSAID-use (continuous vs. on-demand). Radiological progression was presented in probability plots. Statistical interactions were tested using multiple and logistic regression analysis. Differences in radiological progression were analysed using the Chi-square and Mann-Whitney U test.

Results 150 participants randomized to either the continuous-treatment group (n=76), or the on-demand group (n=74) had complete radiographs and were included. The effect of slowing radiological progression with continuous NSAID therapy was more pronounced in patients with elevated ta-CRP-levels, elevated ta-ESR, high ta-ASDAS-CRP or high ta-ASDAS-ESR versus patients with low/normal values. No such effect was found for participants with high vs. low BASDAI. Also, in participants with elevated ta-ESR (irrespective of treatment), there appeared to be a higher rate of structural progression than in participants with normal ta-ESR. Regression analyses showed that continuous NSAID treatment neutralizes the negative effect of inflammation (high ta-ESR).

Conclusions Patients with elevated acute phase reactants seem to benefit most from continuous treatment with NSAIDs. Continuous NSAID-therapy in patients with elevated acute phase reactants may lead to an improved benefit-risk-ratio of these drugs.