Implication of baseline levels and early changes of C-reactive protein for subsequent clinical outcomes of patients with rheumatoid arthritis treated with tocilizumab.

BACKGROUND

Rheumatoid arthritis (RA) is characterised by clinical joint swelling and elevation of acute phase reactant levels, typically measured by the C-reactive protein (CRP). Clinical and inflammatory responses are usually concordant, except for inhibition of IL-6, which often disproportionally reduces the CRP due to direct inhibition of its hepatic production. We investigated whether pre-treatment CRP is a useful marker that can guide a preferential treatment choice towards IL-6 inhibition.

METHODS

Data of 1126 treatment courses with tocilizumab (TCZ; early RA), 250 courses of rituximab (RTX; established RA) and 249 courses of methotrexate (MTX; established RA) were analysed. We compared clinical disease activity index (CDAI) values and change along 24 weeks' follow-up to CRP values at baseline or its early change. We validated the results using data from a separate TCZ trial in early RA.

RESULTS

CRP levels in the TCZ group on average dropped by 74% within 4 weeks. Patients who attained CDAI remission at 24 weeks on TCZ had the highest baseline CRP levels while patients in high disease activity had the lowest; this association was reverse in the RTX and MTX groups. TCZ patients who achieved remission at 24 weeks showed the largest reductions of CRP levels by week 4 compared with those reaching higher disease activity states. Early CRP non-response was indicative of a risk of not achieving clinical treatment goals (p=0.038).

CONCLUSION

Baseline CRP appears to have a positive association with reaching the therapeutic target on TCZ treatment, but is a negative predictor for RTX and MTX. Patients on TCZ without an early CRP response have a lower chance of achieving remission. CRP and its early course may inform, to some extent, the estimation of potential therapeutic success in patients with RA.