• John T Farrar, Andrea B Troxel, Kevin Haynes, Ian Gilron, Robert D Kerns, Nathaniel P Katz, Bob A Rappaport, Michael C Rowbotham, Ann M Tierney, Dennis C Turk, and Robert H Dworkin.
• Department of Biostatistics and Epidemiology, Anesthesiology, and Neurology, University of Pennsylvania, Philadelphia, PA, USA. Electronic address: jfarrar@upenn.edu.
• Pain. 2014 Aug 1;155(8):1622-31.

AbstractThe degree of variability in the patient baseline 7-day diary of pain ratings has been hypothesized to have a potential effect on the assay sensitivity of randomized clinical trials of pain therapies. To address this issue, we obtained clinical trial data from the Food and Drug Administration (FDA) through the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership, and harmonized patient level data from 12 clinical trials (4 gabapentin and 8 pregabalin) in postherpetic neuralgia (PHN) and painful diabetic peripheral neuropathy (DPN). Models were developed using exploratory logistic regression to examine the interaction between available baseline factors and treatment (placebo vs active medication) in predicting patient response to therapy (ie, >30% improvement). Our analysis demonstrated an increased likelihood of response in the placebo-treated group for patients with a higher standard deviation in the baseline 7-day diary without affecting the likelihood of a response in the active medication-treated group, confirming our hypothesis. In addition, there was a small but significant age-by-treatment interaction in the PHN model, and small weight-by-treatment interaction in the DPN model. The patient's sex, baseline pain level, and the study protocol had an effect only on the likelihood of response overall. Our results suggest the possibility that, at least in some disease processes, excluding patients with a highly variable baseline 7-day diary has the potential to improve the assay sensitivity of these analgesic clinical trials, although reductions of external validity must be considered when increasing the homogeneity of the investigated sample.Copyright © 2014 International Association for the Study of Pain. All rights reserved.

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