medwireNews: A score calculated from laboratory results could help to identify whether patients with rheumatoid arthritis (RA) are more likely to respond to treatment with a tumor necrosis factor (TNF) inhibitor or to the interleukin-6 inhibitor tocilizumab, researchers report.
“Currently, although several categories of bDMARDs [biologic disease-modifying antirheumatic drugs] are available, the preferable bDMARD for each RA case is not obvious,” say Yoshinobu Koyama (Japanese Red-Cross Okayama Hospital) and colleagues.
Consequently, TNF inhibitors and tocilizumab “are basically treated as equivalent treatments in the recent disease management recommendations,” they add.
The team took peripheral blood samples from 45 patients with newly diagnosed RA, and identified a significant inverse correlation between messenger RNA levels of IL-6 and TNF-α, “suggesting that the dominant inflammatory cytokine that should be targeted may be different in each RA patient.”
And laboratory data from 27 patients treated with tocilizumab revealed that levels of platelets, hemoglobin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) significantly correlated with the disease activity score (DAS) ratio, calculated from the DAS at 28 joints based on C-reactive protein (DAS28-CRP) at week 24 divided by that at baseline. This relationship was not seen in the 71 patients treated with TNF inhibitors, however.
Based on these findings, Koyama and colleagues developed a score using the four laboratory measures, with 1 point scored for each of the following criteria: platelet count of at least 381 × 103/mm3; hemoglobin of 11.7 g/dL or lower for women and 13.2 g/dL for men; AST levels of 16.0 IU/L or less; and ALT levels of 15.0 IU/L or less.
Among patients who scored 2 or more points, a significantly higher proportion achieved a good response according to EULAR criteria to tocilizumab than to TNF inhibitor treatment, at 66.7% versus 32.5%. A corresponding 0.0% versus 23.3% of participants were classified as treatment nonresponders.
And the differences became “more remarkable” for patients scoring 3 or more points, with 69.2% of those treated with tocilizumab and 19.0% in the TNF inhibitor group achieving a good treatment response, and 0.0% versus 28.6% not responding to treatment.
When cutoffs were defined, a score of 2 points or above predicted a good or moderate tocilizumab response, with a positive predictive value (PPV) of 100.0% and a negative predictive value (NPV) of 20.0%, whereas a score of 1 point or lower predicted a good or moderate TNF inhibitor response, with PPV and NPV values of 71.4% and 21.4%, respectively.
The team validated their findings using data from 228 patients from five different hospitals and found similar results when using the same cutoffs, with PPV and NPV values of 96.8% and 20.9% for tocilizumab-treated patients, and corresponding values of 72.4% and 17.1% for those treated with TNF inhibitors.
These findings “confirmed that the scoring system could be useful to select treatment with either [tocilizumab] or a TNF [inhibitor],” conclude Koyama and colleagues in Arthritis Research & Therapy.
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