title: Effects of fexofenadine, diphenhydramine, and alcohol on driving performance. A randomized, placebo-controlled trial in the Iowa driving simulator.
abstract: BACKGROUND
  Sedating antihistamines may impair driving performance as seriously as alcohol.
  
  
  OBJECTIVE
  To compare the effects of fexofenadine, diphenhydramine, alcohol, and placebo on driving performance.
  
  
  METHODS
  Randomized, double-blind, double-dummy, four-treatment, four-period crossover trial.
  
  
  METHODS
  The Iowa Driving Simulator.
  
  
  METHODS
  40 licensed drivers with seasonal allergic rhinitis who were 25 to 44 years of age.
  
  
  METHODS
  One dose of fexofenadine (60 mg), diphenhydramine (50 mg), alcohol (approximately 0.1% blood alcohol concentration), or placebo, given at weekly intervals before participants drove for 1 hour in the Iowa Driving Simulator.
  
  
  METHODS
  The primary end point was coherence, a continuous measure of participants' ability to match the varying speed of a vehicle that they were following. Secondary end points were drowsiness and other driving measures, including lane keeping and response to a vehicle that unexpectedly blocked the lane ahead.
  
  
  RESULTS
  Participants had significantly better coherence after taking alcohol or fexofenadine than after taking diphenhydramine. Lane keeping (steering instability and crossing the center line) was impaired after alcohol and diphenhydramine use compared with fexofenadine use. Mean response time to the blocking vehicle was slowest after alcohol use (2.21 seconds) compared with fexofenadine use (1.95 seconds). Self-reported drowsiness did not predict lack of coherence and was weakly associated with minimum following distance, steering instability, and leftlane excursion.
  
  
  CONCLUSIONS
  Participants had similar performance when treated with fexofenadine or placebo. After alcohol use, participants performed the primary task well but not the secondary tasks; as a result, overall driving performance was poorer. After participants took diphenhydramine, driving performance was poorest, indicating that diphenhydramine had a greater impact on driving than alcohol did. Drowsiness ratings were not a good predictor of impairment, suggesting that drivers cannot use drowsiness to indicate when they should not drive.
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City 52242-1081, USA. john-weiler@uiowa.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Weiler
authors.forename: J R
authors.initials: JR
authors.lastname: Bloomfield
authors.forename: G G
authors.initials: GG
authors.lastname: Woodworth
authors.forename: A R
authors.initials: AR
authors.lastname: Grant
authors.forename: T A
authors.initials: TA
authors.lastname: Layton
authors.forename: T L
authors.initials: TL
authors.lastname: Brown
authors.forename: D R
authors.initials: DR
authors.lastname: McKenzie
authors.forename: T W
authors.initials: TW
authors.lastname: Baker
authors.forename: G S
authors.initials: GS
authors.lastname: Watson
mesh_terms: D000328:Adult; D001334:Automobile Driving; D018592:Cross-Over Studies; D004155:Diphenhydramine / Q000009:adverse effects*; D004311:Double-Blind Method; D000431:Ethanol / Q000009:adverse effects*; D005260:Female; D006634:Histamine H1 Antagonists / Q000009:adverse effects*; D006801:Humans; D006993:Hypnotics and Sedatives / Q000009:adverse effects; D007484:Iowa; D008297:Male; D008390:Markov Chains; D008875:Middle Aged; D009010:Monte Carlo Method; D010919:Placebos; D006255:Rhinitis, Allergic, Seasonal / Q000188:drug therapy; D012894:Sleep Stages / Q000187:drug effects; D016593:Terfenadine / Q000009:adverse effects / Q000031:analogs & derivatives*
chemical_list: D006634:Histamine H1 Antagonists; D006993:Hypnotics and Sedatives; D010919:Placebos; D000431:Ethanol; D016593:Terfenadine; D004155:Diphenhydramine; C093230:fexofenadine