The OARSI Standing Committee for Clinical Trials Response Criteria Initiative had developed two sets of responder criteria to present the results of changes after treatment in three symptomatic domains (pain, function, and patient's global assessment) as a single variable for clinical trials (1). For each domain, a response was defined by both a relative and an absolute change, with different cut-offs with regard to the drug, the route of administration and the OA localization.
To propose a simplified set of responder criteria with a similar cut-off, whatever the drug, the route or the OA localization.
Data driven approach: (1) Two databases were considered: the "elaboration" database with which the formal OARSI sets of responder criteria were elaborated, and the "revisit" database. (2) Six different scenarios were evaluated: The two formal OARSI sets of criteria; Four proposed scenarios of simplified sets of criteria. Data from clinical randomized blinded placebo controlled trials were used to evaluate the performances of the two formal scenarios with two different databases ("elaboration" versus "revisit") and those of the four proposed simplified scenarios within the "revisit" database. The placebo effect, active effect, treatment effect, and the required sample arm size to obtain the placebo effect and the active treatment effect observed were the performances evaluated for each of the six scenarios. Experts' opinion approach: Results were discussed among the participants of the OMERACT VI meeting, who voted to select the definite OMERACT-OARSI set of criteria (one of the six evaluated scenarios).
Data driven approach: Fourteen trials totaling 1886 OA patients and fifteen studies involving 8164 OA patients were evaluated in the "elaboration"and the "revisit" databases respectively. The variability of the performances observed in the "revisit" database when using the different simplified scenarios was similar to that observed between the two databases ("elaboration" versus "revisit") when using the formal scenarios. The treatment effect and the required sample arm size were similar for each set of criteria. Experts' opinion approach: According to the experts, these two previous performances were the most important of an optimal set of responder criteria. They chose the set of criteria considering both pain and function as evaluation domain and requiring an absolute change and a relative change from baseline to define a response, with similar cut-offs whatever the drug, the route of administration or the OA localization.
This data driven and experts' opinion approach is the basis for proposing an optimal simplified set of responder criteria for OA clinical trials. Other studies, using other sets of OA patients, are required in order to further validate this proposed OMERACT-OARSI set of criteria.