title: Risk of cancer in patients exposed to gabapentin in two electronic medical record systems.
abstract: OBJECTIVE
  High doses of gabapentin were associated with pancreatic acinar cell tumors in male Wistar rats, but there is little published epidemiological data regarding gabapentin and carcinogenicity. We explored the association between gabapentin and cancer in a US medical care program and followed up nominally significant associations in a UK primary care database.
  
  
  METHODS
  In the US Kaiser Permanente Northern California (KPNC) health system, we performed nested case-control analyses of gabapentin and 55 cancer sites and all cancers combined using conditional logistic regression. Up to 10 controls were matched to each case on year of birth, sex, and year of cohort entry. No other covariates were included in models. Only dispensings for gabapentin 2 years or more before index date were considered. Nominally significant associations with an OR > 1.00 and p < 0.05 for three or more dispensings versus no dispensings were followed up by similar nested case-control analyses in the UK General Practice Research Database (GPRD), adjusting for potential indications for gabapentin and risk factors for the specific cancers.
  
  
  RESULTS
  The following analyses had OR > 1.00 and p < 0.05 for three or more dispensings of gabapentin versus no dispensing (2-year lag) in KPNC and were also examined in the GPRD: all cancers, breast, lung and bronchus, urinary bladder, kidney/renal pelvis, stomach, anus/anal canal/anorectum, penis, and other nervous system. These cancers were not statistically significantly associated with gabapentin in the GPRD case-control studies (2-year lag). The GPRD and KPNC studies did not identify a statistically significant increased risk of pancreatic cancer with more than two prescriptions of gabapentin in the 2-year lagged analyses.
  
  
  CONCLUSIONS
  The epidemiological data in a US cohort with up to 12 years of follow-up and a UK cohort with up to 15 years of follow-up do not support a carcinogenic effect of gabapentin use. However, the confidence intervals for some analyses were wide, and an important effect cannot be confidently excluded.
authors.affiliation: WW Epidemiology, GlaxoSmithKline, Research Triangle Park, NC, USA. michael.c.irizarry@gsk.com
authors.forename: Michael C
authors.initials: MC
authors.lastname: Irizarry
authors.forename: David J
authors.initials: DJ
authors.lastname: Webb
authors.forename: Nada
authors.initials: N
authors.lastname: Boudiaf
authors.forename: John
authors.initials: J
authors.lastname: Logie
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Habel
authors.forename: Natalia
authors.initials: N
authors.lastname: Udaltsova
authors.forename: Gary D
authors.initials: GD
authors.lastname: Friedman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000588:Amines / Q000009:adverse effects*; D000927:Anticonvulsants / Q000009:adverse effects*; D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D015331:Cohort Studies; D003509:Cyclohexanecarboxylic Acids / Q000009:adverse effects*; D016208:Databases, Factual / Q000706:statistics & numerical data; D057286:Electronic Health Records / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D000077206:Gabapentin; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology / Q000209:etiology* / Q000473:pathology; D012306:Risk; D006113:United Kingdom / Q000453:epidemiology; D014481:United States / Q000453:epidemiology; D005680:gamma-Aminobutyric Acid / Q000009:adverse effects*
chemical_list: D000588:Amines; D000927:Anticonvulsants; D003509:Cyclohexanecarboxylic Acids; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin