To answer the question whether or not therapeutic methadone doses significantly reduce traffic-related performance of drivers on medically supervised methadone programmes, 34 methadone substitution patients, all of them volunteers, were subjected to a test series: the focus of the study was a psychophysical test battery consisting of 10 individual performance tests to assess essential functions with regard to driving ability, such as concentration, attention, reaction capability, memory, perception and sensorimotor co-ordination. In evaluating the results of the psychophysical tests, multiple drug use and subjective methadone influence at the time of the examination were taken into consideration but current methadone blood level was neglected. The results were compared to those of a control group. The methadone group (n = 34) consisted of 25 men and 9 women aged between 18 and 38. At the time of the study, the majority of the test persons (29) were on low dosage methadone maintenance (up to 60 mg/day). In the urine samples of approximately 2/3 of the test persons, evidence was found for multiple drug use together with other psychotropic substances, the most frequent (14) being cannabis metabolites. Referring to their driving practices, a mere 4 out of 29 drivers had not committed any driving offences. A comparison of the psychophysical performance of the whole methadone group (n = 34) with a control group demonstrated that the methadone substitution patients achieved rather lower results in almost all variables. These performance deficits were particularly conspicuous in sustained attention, sensorimotor co-ordination and reaction capability. 12 "methadone only" participants, i.e. methadone probands without any additional consumption of psychotropic substances showed-partly considerably-better performance than the methadone group as a whole and also achieved normal results in relation to the test norm. Nevertheless, once again, results tended to be of lower level in comparison to the control group. "Methadone only" substitution patients, in particular those volunteers without a current subjective methadone influence-reached practically the same results as the corresponding control subjects, or at least average results based on test norm. However, the study revealed distinctive performance impairment (e.g. in sustained attention, reaction capability) when other psychotropic substances (including alcohol and cannabis!) were taken as well during the subjective methadone phase. The performance deficits were predominantly caused by a slowing down of reactions. Our study illustrates that, under certain conditions, long-term methadone maintenance under strict medical supervision does not have any significant unfavourable impact on the psychophysical performances in driving ability as examined in this study. Thus, these research findings support the previous Zurich experiences, according to which driving ability -- and in the end also driving aptitude -- of the methadone substitution patients does not depend on the methadone therapy itself, nor on the amount of the daily methadone intake. In making the final medical judgement on driving ability, the presence of a mixed drug use and the personality of the person in question are of far greater importance. For the website of the journal see http://www.smw.ch/ (Author/publisher)
Samenvatting