Heroin-using drivers: importance of morphine and morphine-6-glucuronide on late clinical impairment

Objective To evaluate the relationship between major heroin metabolites (morphine, morphine-6-glucoronide), pattern of drug use, and late impairment of psychomotor functions. Methods From the database of the Norwegian Institute of Public Health, Oslo, blood morphine concentration in samples from heroin users (n=70) containing only morphine were correlated with results of the clinical test for impairment (CTI). For comparison, test results were explored in individuals without any positive analytical finding in blood samples (n=79) selected from the same database. Results In the "no drug" cases, 86% were judged as not impaired and 14% as impaired. In the morphine only cases, 20% were judged as not impaired, and 80% as impaired. Both daily users and non-daily users had the same proportion of impaired cases. Median blood morphine concentration (M) was 0.09 mu mol/l in the "not impaired" group and 0.15 mu mol/l in the "impaired" group (P=0.067). For morphine-6-glucuronide (M6G), the median blood concentration was 0.09 mu mol/l in the "not impaired" group and 0.14 mu mol/l in the "impaired" group (P=0.030). A significant correlation between concentration quartiles and number of cases determined as "impaired" was found for M6G (P=0.018) and for the sum M+M6G (P=0.013). Conclusion In our population of heroin-drugged drivers, blood concentrations of M6G and the sum M+M6G appeared to have concentration-dependent effects on the CNS that may lead to impairment as judged from a CTI. Variations in pattern of use did not seem to have any bearing on the judgement of impairment.