Opioids and Driving Ability: Current Data do not Support One Opioid Being More Favorable Than Another

To the Editor: Miceli et al. conclude from the reaction time measurements taken on a single subject that tramadol and oxycodone/naloxone differ in their propensity to cause car accidents. This conclusion is not supported by the evidence presented. Repeated measurement procedures can provide valid statistical results with a limited number of subjects, but the statistical assumptions underlying the model cannot be validated with only one subject. Also, the single patient conclusion cannot control for potential predictive and prognostic factors that could have influenced the result. Indeed, differences in the testing results could be explained by many factors, not only the difference in drug treatment. One explanation could be a training effect (commonly termed a period effect) producing faster reaction times at the second study session. Any of the factors that influence reaction time (e.g. sleepiness, distraction) could also have had greater or lesser effects on different study days. Furthermore, the difference could only be detected after additional statistical testing. It is significant that the results obtained with both drugs “would allow the subject to drive vehicles. ”, so the postulated statistical difference had no clinical implication. Of particular importance, the International Council on Alcohol, Drugs, and Traffic Safety recommendations state that a test battery to measure driver fitness should include divided attention, motor response, sustained attention (vigilance), and accuracy of decisionmaking, among other parameters. Simple tests measuring only visual and auditory reaction times fail to provide deeper insight into the complexity of driving a vehicle. The current ICADT classification of psychoactive medication is not based on the proposed test battery and should therefore be interpreted with caution. There are study data demonstrating that tramadol/paracetamol has less impact on vigilance (choice reaction time, somnolence) than codeine/paracetamol. Jamison et al. found no differences between transdermal fentanyl and oxycodone/acetaminophen in their effect on neuropsychological performance, and a series of studies using identical methodology demonstrated that the performance of chronic pain patients receiving transdermal buprenorphine, fentanyl, or sustained-release oxycodone did not differ significantly from an ageindependent control group. In a recent study, patients treated with sustained-release or transdermal opioids (morphine, fentanyl, oxycodone, hydromorphone, buprenorphine) performed an on-the-road driving test. No difference was found in the primary outcome parameter – standard deviation of lateral position (SDLP) – between patients and healthy controls. There is currently no gold standard for assessing driving ability while receiving opioids, and available data do not support the conclusion that one opioid is more favorable than others. Systematic reviews of published data on driving ability and opioids found high between-subject variability, and that study results may be influenced by many factors. These include trial methodology, patient selection, and confounding factors such as pain severity, co-medication, sleep disturbance and fatigue, and comorbid psychiatric and psychological disorders. In line with these results, the summaries of product characteristics of opioids such as oxycodone and tramadol similarly indicate that driving ability maybe impaired. Owing to the individual variability of response and the impact of other factors (e.g., pain intensity, co-morbidity), recommendations on whether or not to drive should be made on an individual basis.