Background/Purpose: In addition to the assessment of the two co-primary endpoints – pain and function – regulatory agencies recommend the use of responder rates in percentages as complementary endpoints in order to demonstrate the robustness of the results and their clinical relevance at the level of the individual. Several clinically meaningful responder definitions were in fact proposed by the OMERACT initiative and the OARSI.

Methods: The proportion of responders was calculated among the subjects participating in the CONCEPT study, a double-blind, double-dummy Phase III clinical trial in which they received pharmaceutical grade Chondroitin Sulfate (CS) (800 mg/day, during 6 months) or placebo (PL). The following responder definitions were used: pain reduction of 30% vs baseline (moderate pain relief), pain reduction of 40% vs baseline (moderate-to-substantial pain relief), pain reduction of 50% vs baseline (substantial pain relief). Corresponding responder rates were calculated for the decrease in Lequesne index (LI). Moreover, the rates according to the OMERACT-OARSI responder criteria (scenario F) were calculated.

Results: 404 of the 604 patients recruited in 5 European countries for the CONCEPT study, suffering from knee osteoarthritis (OA) corresponding to the ACR criteria and belonging to the intention to treat population of the study, were included in the analyses. Of these, 199 were treated with CS and 205 with PL. The remaining 200 patients in the control group with active treatment (celecoxib 200 mg/day) were not considered. The responder rates for pain reduction were consistently higher for the CS group than for the PL group. They were 69% and 61% in the CS and the PL group, respectively, for a pain reduction of 30% vs baseline (p=0.098 between groups, chi-square test), 64% and 52% for a pain reduction of 40% vs baseline (p=0.014), and 58% and 40% for a pain reduction of 50 % vs baseline (p<0.001). Comparable results were found for the LI. According to the OMERACT-OARSI criteria (scenario F), 66% and 55% of the patients in the CS and the PL group, respectively, were found to be responders after the 6-months of treatment (p=0.021 between groups, chi-square test).

Conclusion: Higher percentages of patients with knee osteoarthritis treated continuously for 6 months with 800 mg/day of pharmaceutical grade Chondroitin Sulfate achieved pre-defined levels of pain relief and/or functional improvement as compared to those receiving placebo. The differences in responder rates were both, statistically significant and clinically relevant.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/chondroitin-sulfate-reduces-pain-and-improves-function-in-knee-osteoarthritis-significantly-better-than-placebo-independently-of-the-definition-of-responders/