Prevalence of gabapentin in impaired driving cases in Washington State in 2003-2007

Gabapentin (Neurontin) is an antiepileptic drug commonly prescribed for pain treatment. In the past 15 years, indications for gabapentin have been increasing even though the complete mechanism of action is unknown. Side effects include somnolence, dizziness, ataxia, nystagmus, and fatigue. This study reviewed all cases positive for gabapentin submitted to the Washington State Toxicology Laboratory between January 2003 and December 2007. The concentrations of gabapentin in blood from impaired driving cases (n = 137) ranged from < 2.0 to 24.7 mg/L with a mean of 8.4 +/- 5.4 mg/L and a median of 7.0 mg/L. The driving population was 50% male with a mean age of 43.0 +/- 10.9 years (range 23-73). Of the cases studied, only 7% were positive for gabapentin alone with the remaining 93% indicative of polydrug use. Drug Recognition Expert reports from four cases in which the only drug detected likely to be causing impairment was gabapentin were examined. These reports demonstrated that subjects may exhibit psychophysical indicators of a central nervous system depressant (e.g., horizontal gaze nystagmus, poor performance on standardized field sobriety tests) with clinical indicators (e.g., dilated pupils, low body temperature, and elevated pulse and blood pressure) that are not consistent with a depressant.