Gary D Friedman1,2, Ninah Achacoso1, Laurel A Habel1. 1. Division of Research, Oakland, CA. 2. Department of Health Research and Policy, Stanford University School of Medicine, CA.
Abstract
CONTEXT: Epidemiologic analyses of gabapentin use and cancer risk in Kaiser Permanente Northern California were previously carried out in a collaborative study and independently evaluated in a UK database. OBJECTIVE: To update these epidemiologic analyses with 7.5 more years of follow-up. DESIGN: Case-control analyses using conditional logistic regression to estimate relative risk by odds ratios using the prior collaboration's criteria for identifying positive drug-cancer associations and our more stringent criteria requiring stronger association, lower p values, and evidence of dose response. New associations were reanalyzed with additional control for limited measures of smoking and alcohol use. MAIN OUTCOME MEASURES: Gabapentin-cancer associations. RESULTS: No previously found associations met our stringent criteria, but cancers of the mouth/pharynx, esophagus, liver, and vagina did. All odds ratios for 3 or more and 8 or more prescriptions were moderately reduced by control for smoking and alcohol. Substantial elevations of risk of mouth/pharynx, liver, and vaginal cancers were associated with only 1 prescription dispensed. Sensitivity analyses aimed at possible confounding and other biases did not change our conclusions but did reveal a markedly increased risk of vaginal cancer in gabapentin users with epilepsy compared with users without. CONCLUSION: The reduced magnitude of relative risk with control for smoking and alcohol use suggests confounding by known risk factors. Biologically implausible elevated risk from just 1 prescription suggests confounding by indication. Either or both of these concerns applies to each of the 4 cancer sites associated with gabapentin use. Updated analyses show little if any evidence for carcinogenic effects of gabapentin.
CONTEXT: Epidemiologic analyses of gabapentin use and cancer risk in Kaiser Permanente Northern California were previously carried out in a collaborative study and independently evaluated in a UK database. OBJECTIVE: To update these epidemiologic analyses with 7.5 more years of follow-up. DESIGN: Case-control analyses using conditional logistic regression to estimate relative risk by odds ratios using the prior collaboration's criteria for identifying positive drug-cancer associations and our more stringent criteria requiring stronger association, lower p values, and evidence of dose response. New associations were reanalyzed with additional control for limited measures of smoking and alcohol use. MAIN OUTCOME MEASURES: Gabapentin-cancer associations. RESULTS: No previously found associations met our stringent criteria, but cancers of the mouth/pharynx, esophagus, liver, and vagina did. All odds ratios for 3 or more and 8 or more prescriptions were moderately reduced by control for smoking and alcohol. Substantial elevations of risk of mouth/pharynx, liver, and vaginal cancers were associated with only 1 prescription dispensed. Sensitivity analyses aimed at possible confounding and other biases did not change our conclusions but did reveal a markedly increased risk of vaginal cancer in gabapentin users with epilepsy compared with users without. CONCLUSION: The reduced magnitude of relative risk with control for smoking and alcohol use suggests confounding by known risk factors. Biologically implausible elevated risk from just 1 prescription suggests confounding by indication. Either or both of these concerns applies to each of the 4 cancer sites associated with gabapentin use. Updated analyses show little if any evidence for carcinogenic effects of gabapentin.
Authors: Michael C Irizarry; David J Webb; Nada Boudiaf; John Logie; Laurel A Habel; Natalia Udaltsova; Gary D Friedman Journal: Pharmacoepidemiol Drug Saf Date: 2011-12-06 Impact factor: 2.890
Authors: Gary D Friedman; Natalia Udaltsova; James Chan; Charles P Quesenberry; Laurel A Habel Journal: Cancer Causes Control Date: 2009-12 Impact factor: 2.506