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An evaluation of the FDA responder endpoint for IBS-C clinical trials
Analysis of data from linaclotide phase 3 clinical trials
Macdougall, JE., Johnston, JM., Lavins, BJ., Nelson, L., Williams, V., Carson, RT., Shiff, SJ., Shi, K., Kurtz, CB., Baird, MJ., Currie, MG., & Lembo, AJ. (2013). An evaluation of the FDA responder endpoint for IBS-C clinical trials: Analysis of data from linaclotide phase 3 clinical trials. Neurogastroenterology and Motility, 25(6), 481-486. https://doi.org/10.1111/nmo.12089
Background Our objective was to evaluate the performance of the Food and Drug Administration (FDA) Responder Endpoint for clinical trials in IBS-C, using data from two large Phase 3 clinical trials of linaclotide. The FDA interim endpoint requires that, for 50% of trial weeks, patients report 30% decrease in Abdominal Pain at its worst and (in the same week) an increase in Complete Spontaneous Bowel Movements (CSBMs) of 1 from baseline. Methods Anchor-based methodology was used to estimate thresholds of clinically meaningful change using symptom-specific patient rating of change questions (PRCQs) and symptom severity questions. The diagnostic accuracy of the FDA Responder Endpoint was assessed using sensitivity/specificity-based methods. Key Results Using anchor-based methods, the estimates of the clinically meaningful improvement thresholds for Abdominal Pain ranged from 25.9% to 32.4% and thresholds for increase in weekly CSBM rate ranged from 1.4 to 1.6 CSBMs per week. Compared with the symptom-specific PRCQs for patient rating of relief, the FDA Responder Endpoint has a sensitivity of 60.7%, a specificity of 93.5%, and an accuracy of 82.0%. Changing the number of weeks required to be a responder or the percentage improvement in the Abdominal Pain criteria did not result in notable improvement in the accuracy of the FDA Responder Endpoint. Conclusions & Inferences The FDA Responder Endpoint for IBS-C clinical trials represents clinically meaningful improvements in IBS-C symptoms for patients with excellent specificity and reasonable sensitivity