EFFECTS ON DRIVING ABILITY
Opioid drugs are central nervous system depressants, used in the treatment of cancer pain and chronic nonmalignant pain. Although there is common acceptance that opioid-naïve patients should be instructed not to drive, there is controversy surrounding recommendations that should be made to patients taking stable opioid doses. Fishbain, Cutler, Rosomoff, and Rosomoff (2003) conducted a structured, evidence-based review of the literature between 1966 and 2001 to determine whether opioids affect the driving ability of patients who are on stable doses of this medication or who would be presumed to have developed some tolerance to the sedative effects of opioids. Twenty-three studies on the effects of stable opioid doses on psychomotor abilities were reviewed. Results indicated that 16 (70%) of the studies supported a conclusion of no effect on psychomotor abilities. This indicates “moderate evidence, generally consistent findings” of no impairment of psychomotor abilities according to Agency for Health Care Policy and research (AHCPR) guidelines (Institute of Medicine Committee to advise the Public Health Service on Clinical Practice, 1990).
Fishbain et al. (2003) reviewed 11 studies on the effects of stable doses of opioids on cognitive abilities. Only 5 (45%) of these studies supported a conclusion of no effect on cognitive function. The evidence on the effects of stable doses of opioids on the cognitive abilities necessary for safe driving may therefore be regarded as “inconclusive” according to AHCPR guidelines.
Fifteen studies were reviewed to determine the effects of new opioid dosing on psychomotor abilities (Fishbain et al., 2003). As 14 (93%) of the studies supported a conclusion of no effect on psychomotor function, it was concluded that there was “strong evidence, consistent findings” of no impairment of psychomotor abilities for acute opioid administration, using the quantitative method described by the AHCPR guidelines.
Fishbain et al. (2003) reviewed seven studies to determine the effect of stable opioid dosing on motor vehicle crashes, violations, and convictions compared to the general population. As 6 (86%) of the studies supported no effect, this indicated “strong evidence, consistent findings” of no more crashes, convictions, or violations among opioid-dependent patients as compared to the general population.
Four studies were reviewed by Fishbain et al. (2003) to determine whether there were impairments on driving for patients on stable opioids, compared to controls, using driving simulators or on-road driving measures. As 3 of the 4 studies (75%) supported a conclusion of no effect, this indicated “strong evidence, consistent findings” for no impairment of driving performance, using simulator or on-road measures.
Fishbain et al. (2003) suggest that there may have been confounding variables to explain the inconsistent evidence in the cognitive impairment studies, which could have also confounded the results of the studies reviewed on psychomotor abilities, crashes/convictions/violations, and driving performance in simulators and on-road. Confounding factors include pain level (e.g., higher levels of pain interfere with psychomotor/cognitive function), education level, disease state (disease-associated symptoms such as fatigue), and history of drug/alcohol abuse or dependence.
Of particular interest to the present review, Fishbain et al. (2003) provided recommendations about how future research on the effects of opioid drugs and driving ability can be improved. First, future psychomotor and cognitive studies should control for pain, educational status, and history of drug/alcohol abuse/dependence, besides controlling for sex and age. In addition, studies can be improved by using different types of control groups. In the reviewed studies, a treatment group (patients placed on opioids) was compared to a control group (patients not on opioids). This leads to a situation where the effects of a patient’s disease state (e.g., cancer/fatigue, pain, etc.) are not controlled for. A better control group could be to use the patients as their own controls. Then, psychomotor and cognitive studies could be performed pre-opioid placement and post-opioid placement and compared. Of the 3 studies reviewed with this design, all 3 found no opioid effect on cognitive or psychomotor abilities. Another possible improvement recommended to this type of research is to include a patient control group. In this case, include a cancer patient opioid-free control group to compare to the cancer patients placed on opioids and to a control group of opioid-free nonpatients. A final improvement (Zacny, 1995) is the use of a positive control as a benchmark. In this instance, a patient would be given drugs that are known to affect cognitive and psychomotor performance, such as diazepam. Opioid effects would then be compared not only to opioid-free controls, but to this positive control group. This has the advantage of comparing opioid impairment (if any) to a benchmark.