Outcome reporting in industry-sponsored trials of gabapentin for off-label use.
BACKGROUND
There is good evidence of selective outcome reporting in published reports of randomized trials.


METHODS
We examined reporting practices for trials of gabapentin funded by Pfizer and Warner-Lambert's subsidiary, Parke-Davis (hereafter referred to as Pfizer and Parke-Davis) for off-label indications (prophylaxis against migraine and treatment of bipolar disorders, neuropathic pain, and nociceptive pain), comparing internal company documents with published reports.


RESULTS
We identified 20 clinical trials for which internal documents were available from Pfizer and Parke-Davis; of these trials, 12 were reported in publications. For 8 of the 12 reported trials, the primary outcome defined in the published report differed from that described in the protocol. Sources of disagreement included the introduction of a new primary outcome (in the case of 6 trials), failure to distinguish between primary and secondary outcomes (2 trials), relegation of primary outcomes to secondary outcomes (2 trials), and failure to report one or more protocol-defined primary outcomes (5 trials). Trials that presented findings that were not significant (P > or = 0.05) for the protocol-defined primary outcome in the internal documents either were not reported in full or were reported with a changed primary outcome. The primary outcome was changed in the case of 5 of 8 published trials for which statistically significant differences favoring gabapentin were reported. Of the 21 primary outcomes described in the protocols of the published trials, 6 were not reported at all and 4 were reported as secondary outcomes. Of 28 primary outcomes described in the published reports, 12 were newly introduced.


CONCLUSIONS
We identified selective outcome reporting for trials of off-label use of gabapentin. This practice threatens the validity of evidence for the effectiveness of off-label interventions.
Vedula
S Swaroop
SS
Center for Clinical Trials, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA. svedula@jhsph.edu
Bero
Lisa
L
Scherer
Roberta W
RW
Dickersin
Kay
K
D000588:Amines / Q000627:therapeutic use*; D001714:Bipolar Disorder / Q000188:drug therapy; D002985:Clinical Protocols; D003509:Cyclohexanecarboxylic Acids / Q000627:therapeutic use*; D000077206:Gabapentin; D006801:Humans; D008881:Migraine Disorders / Q000188:drug therapy; D056687:Off-Label Use / Q000706:statistics & numerical data; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000592:standards; D010146:Pain / Q000188:drug therapy; D017594:Publication Bias; D016032:Randomized Controlled Trials as Topic / Q000592:standards; D016896:Treatment Outcome; D005680:gamma-Aminobutyric Acid / Q000627:therapeutic use*
D000588:Amines; D003509:Cyclohexanecarboxylic Acids; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin