The clinical importance of changes in the 0 to 10 numeric rating scale for worst, least, and average pain intensity: analyses of data from clinical trials of duloxetine in pain disorders.
Data on 1,700 patients pooled from 5 randomized, placebo-controlled duloxetine studies (3 in diabetic peripheral neuropathic pain and 2 in fibromyalgia) were analyzed to determine clinically important differences (CIDs) in the 0 to 10 Numeric Rating Scale-Pain Intensity (NRS-PI) for patient-reported "worst" and "least" pain intensity while validating the previously published level for "average" pain. The correspondence between the baseline-to-endpoint raw and percentage change in the NRS-PI for the worst, least, and average pain were compared to patients' perceived improvements at endpoint as measured by the 7-point Patient Global Impression of Improvement (PGI-I) scales. Stratification by baseline pain separated the raw but not the percent change scores. The PGI-I category of "much better" or above was our a priori definition of a CID. Cutoff points for the NRS-PI change scores were determined using a receiver operator curve analysis. A consistent relationship between the worst and average NRS-PI percent change and the PGI-I was demonstrated regardless of the study, pain type, age, sex, or treatment group with a reduction of approximately 34%. The least pain item CID was slightly higher at 41%. Raw change CID cutoff points were approximately -2, -2.5 and -3 for least, average, and worst pain respectively.


CONCLUSIONS
We determined an anchor-based value for the change in the worst, least, and average pain intensity items of the Brief Pain Inventory that best represents a clinically important difference. Our findings support a standard definition of a clinically important difference in clinical trials of chronic-pain therapies.
Farrar
John T
JT
Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA19041, USA. jfarrar@mail.med.upenn.edu
Pritchett
Yili L
YL
Robinson
Michael
M
Prakash
Apurva
A
Chappell
Amy
A
D018759:Adrenergic Uptake Inhibitors / Q000627:therapeutic use*; D000368:Aged; D004185:Disability Evaluation; D004311:Double-Blind Method; D000068736:Duloxetine Hydrochloride; D005260:Female; D005356:Fibromyalgia / Q000188:drug therapy; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D010147:Pain Measurement / Q000379:methods*; D012372:ROC Curve; D016032:Randomized Controlled Trials as Topic; D012720:Severity of Illness Index; D013001:Somatoform Disorders / Q000188:drug therapy*; D013876:Thiophenes / Q000627:therapeutic use*; D016896:Treatment Outcome
D018759:Adrenergic Uptake Inhibitors; D013876:Thiophenes; D000068736:Duloxetine Hydrochloride