A two-sample approach to retrograde extrapolation of blood THC concentrations - Is it feasible?

BACKGROUND

Retrograde extrapolation of drug concentrations in blood can be relevant in cases of drug-impaired driving and is regularly used in forensic toxicology in Norway. Δ9-tetrahydrocannabinol (THC) has complex, multi-compartmental pharmacokinetics, which makes retrograde extrapolation of blood THC concentrations problematic. In the present study, we evaluated an approach to retrograde extrapolation in which momentary rates of decrease of THC were estimated from two consecutive blood samples in apprehended drivers.

MATERIAL AND METHODS

Data were collected from apprehended drivers in Norway 2000-2020. We included 548 cases in which THC was detected in two consecutive blood samples collected ≥ 20 min apart. THC concentrations were measured by GC-MS and UHPLC-MS/MS. In each case, THC concentrations and the time between the two sampling points (Δt) were used to estimate the rate constant k. The relationship between THC concentration and k was modelled by linear regression.

RESULTS

The median Δt was 31 min (interquartile range, IQR = 9). The median blood THC concentration was 2.4 μg/L (IQR = 3.4) at the first sampling point and 2.3 μg/L (IQR =3.1) at the second. The concentration decreased in 62% and increased in 38% of all cases. However, considering measurement uncertainty, the changes were not statistically significant in 87% of cases. The mean of k was 0.12 h-1, corresponding to an apparent t1/2 of 6.0 h. The t1/2 predicted from linear regression of k against THC concentration ranged from 0.93 to 13 h for the highest and lowest concentrations observed (36 and 0.63 μg/L, respectively). The time from driving to blood collection had a median of 1.7 h (IQR = 1.5), and did not correlate with k.

CONCLUSIONS

The apparent t1/2 of THC calculated from the mean of k was 6.0 h, which is shorter than the terminal elimination t1/2 suggested in previous population studies. This indicates that blood samples were often taken during the late distribution phase of THC. Because Δt was short relative to the rates of decrease expected in the late distribution and elimination phases, the underlying true concentration changes related to in vivo pharmacokinetics were small and masked by the relatively larger "false" changes introduced by random analytical and pre-analytical error. Therefore, individual values of k calculated from only two blood samples taken a short time apart are unreliable, and a two-sample approach to retrograde extrapolation of THC cannot be recommended.

Driving under the influence of zopiclone: Elimination between two consecutive blood samples

AIM

Zopiclone is a widely used hypnotic drug which is frequently detected in apprehended drivers. For assessments in forensic cases, the elimination half-life (t1/2) of a drug is sometimes important. A t1/2 of 3.5-6.5 h for zopiclone is previously reported in healthy individuals, but different factors like age and drug-interactions can affect the t1/2 of zopiclone. The aim of this study was to describe concentrations of zopiclone and co-ingestion of additional drugs in apprehended drivers, and to investigate the t1/2 of zopiclone based on two consecutive blood samples.

METHODS

Data was collected from apprehended drivers in Norway between 2003 and 2021. All cases where zopiclone was detected were included. In a subset of the material, two consecutive whole blood samples were collected ≥ 20 and < 60 min apart. Concentrations of zopiclone in blood were determined by LC-MS or UHPLC-MS/MS. The elimination and t1/2 of zopiclone was estimated from the concentration change of zopiclone and the time interval between the two consecutive blood samples, under the assumption of first order kinetics.

RESULTS

The median concentration among all zopiclone positive cases was 0.044 mg/L (IQR 0.070 mg/L) (n = 2401). The most frequent additional drugs detected were ethanol (36%), diazepam (22%), amphetamine (14%) and THC (14%). In zopiclone-only cases (n = 364), the median concentration of zopiclone was 0.066 mg/L (IQR 0.115 mg/L). In 112 cases, two consecutive blood samples were collected. Of these, 28 cases showed increasing concentrations of zopiclone between the two sampling time points. Among the cases in which the concentration decreased (n = 84), the median C1 was 0.048 mg/L (IQR 0.062 mg/L) and the median C2 was 0.043 mg/L (IQR 0.056 mg/L). A Bayesian statistical model was used to obtain the posterior distribution of t1/2. The posterior median of t1/2 was estimated to 3.1 h (IQR=0.39 h) when including only the cases showing decreasing concentrations, and this increased to 3.8 h (IQR=0.52 h) when also including samples showing non outlying increase in concentrations. There was no statistically significant gender difference in the calculated half-lives (two-sided Mann-Whitney U test, p = .525).

CONCLUSIONS

This study showed that zopiclone is frequently detected in apprehended drivers in supra therapeutic concentrations and poly drug cases. The elimination of zopiclone in blood from two consecutive blood samples indicated an apparent t1/2 of between 3.1 and 3.8 h, which is within the lower range of what previous experimental studies on healthy individuals have reported.

Nystagmus among suspected amphetamine impaired drivers

Clinical signs of drug use can be helpful to identify which drug has been consumed. Amphetamine intake has traditionally not been considered to cause nystagmus. The aim of this study was to explore whether there is a relationship between amphetamine use and nystagmus in a population of apprehended drivers in a naturalistic setting. We evaluated drivers suspected of drug-impaired driving where blood samples were collected and a clinical test of impairment (CTI) was performed. Evaluation of nystagmus is one of the CTI subtests. The samples were analysed for alcohol and psychoactive drugs. Cases with a nystagmus test were recorded and amphetamine-only cases were compared with alcohol-only cases and with cases where alcohol or drugs were not detected, respectively. Samples from 507 amphetamine-only cases were compared to 485 alcohol-only cases and 205 drug-negative cases. The median blood amphetamine concentration was 0.37 mg/L and the median alcohol concentration was 1.57 g/kg. The proportion of cases with nystagmus was similar in amphetamine-only cases (21%) and drug-negative controls (25%), p = 0.273, but higher in alcohol-only cases (53%), p < 0.001. No association was found between the blood amphetamine concentration and degree of nystagmus (Spearman's ρ = 0.008, p = 0.860), whereas an association between blood alcohol concentration and degree of nystagmus was demonstrated (ρ = 0.249, p < 0.001). In conclusion, our study did not find that apprehended drivers using amphetamine had more frequently nystagmus than a control group that tested negative for alcohol and drugs, even at high amphetamine concentrations in blood. Hence, nystagmus should not be considered a tool for identifying amphetamine-induced impairment in drivers.

A clinical trial on the acute effects of methadone and buprenorphine on actual driving and cognitive function of healthy volunteers

Aims

The present study assessed the acute effects of methadone and buprenorphine on actual on‐road driving performance and neurocognitive function.

Methods

Methadone (5 and 10 mg per os) and buprenorphine (0.2 and 0.4 mg sublingual) were administered to 22 healthy volunteers in a five‐way, double‐blind, randomized, placebo‐controlled, double‐dummy, cross‐over study. Driving performance was assessed with an on‐road driving test. The primary outcome measure was standard deviation of lateral position (SDLP), a measure of road tracking control. Laboratory tests were used to measure cognitive function (e.g. reaction time and attention) and questionnaires were used to assess subjective measures of mood and sedation.

Results

There was no significant main effect of treatment on SDLP. Yet, analysis of individual drug‐placebo contrast data revealed that buprenorphine 0.4 mg significantly increased SDLP. Driving impairment was mild and below the impairment threshold of a blood alcohol concentration of 0.5 mg ml⁻¹. Four participants stopped their driving test while under the influence of either opioid due to sleepiness. Both opioids produced impairments of cognitive task performance and increased sleepiness particularly at the highest dose.

Conclusions

Analgesic doses of buprenorphine produced mild impairing effects on driving and related cognitive skills, while methadone impaired cognitive task performance but not driving performance. Large individual variations were observed for both drugs. Patients should be informed about the possibility of driving impairment when initiating opioid treatment.

Acute impairing effects of morphine related to driving: A systematic review of experimental studies to define blood morphine concentrations related to impairment in opioid-naïve subjects

OBJECTIVE

The objective of this study was to look for dose- and concentration-effect relationships in experimental studies on single-dose administration of morphine on traffic-relevant behavioral tests by a systematic literature review and possibly to see whether a dose/concentration could be defined below which few or no tests would be affected.

METHODS

Searches for corresponding literature were conducted using MEDLINE, EMBASE, and PsycINFO, throughout March of 2016. The search strategy consisted of words colligated to cognitive and psychomotor functions of relevance to driving, in relation to morphine administration. The tests were arranged in main groups, and tests showing impairment were categorized by doses as well as calculated plasma concentrations.

RESULTS

Fifteen studies were included in the review. Impairment after the administration of a single intravenously dose of morphine was found in some of the tests on reaction time, attention, and visual functions. No impairment was observed in tests on psychomotor skills and en-/decoding. Tests on reaction time appeared to be less sensitive to the morphine administration, whereas tests on visual functions and attention appeared to be the most sensitive to the morphine administration. Single-dose administration of morphine with dosages up to 5 mg appeared to cause very few effects on traffic-relevant performance tasks. At higher dosages, impairment was found on various tasks but with no clear dose-effect relationship. Plasma morphine concentrations less than 50 nmol/L are most probably accompanied by few effects on traffic-relevant performance tasks.

CONCLUSIONS

A plasma morphine concentration of 50 nmol/L (approximately 14.3 ng/mL) could represent an upper level, under which there is little accompanying road traffic risk. A single dose of 5 mg morphine IV and analgetic equivalence doses of fentanyl, hydromorphone, oxycodone, and oxymorphone are presented with the suggestion that few traffic-relevant effects will appear after such doses.

Conversion factors for assessment of driving impairment after exposure to multiple benzodiazepines/z-hypnotics or opioids

AIMS

Norway has introduced legal concentration limits in blood for 28 non-alcohol drugs in driving under the influence cases. As of 2016 this legislation also regulates the assessment of combined effects of multiple benzodiazepines and opioids. We herein describe the employed methodology for the equivalence tables for concentrations of benzodiazepines/z-hypnotics and opioids implemented in the Norwegian Road Traffic Act.

METHODS

Legislative limits corresponding to impairment at blood alcohol concentrations (BAC) of 0.02%, 0.05% and 0.12% were established for 15 different benzodiazepines and opioids. This was based on a concept of a linear relationship between blood drug concentration and impairment in drug naïve users. Concentration ratios between these drugs were used to establish conversion factors and calculate net impairment using diazepam and morphine equivalents.

RESULTS

Conversion factors were established for 14 benzodiazepines/z-hypnotics (alprazolam, bromazepam, clobazam, clonazepam, etizolam, flunitrazepam, lorazepam, nitrazepam, nordiazepam, oxazepam, phenazepam, temazepam, zolpidem and zopiclone) and two opioids (methadone and oxycodone).

CONCLUSIONS

Conversion factors to calculate diazepam and morphine equivalents for benzodiazepines/z-hypnotics and selected opioids, respectively, have been operative in the Norwegian Road Traffic Act as of February 2016. Calculated equivalents can be applied by the courts to meter out sanctions.

THC and CBD in blood samples and seizures in Norway: Does CBD affect THC-induced impairment in apprehended subjects?

BACKGROUND AND AIMS

Several publications have suggested increasing cannabis potency over the last decade, which, together with lower amounts of cannabidiol (CBD), could contribute to an increase in adverse effects after cannabis smoking. Naturalistic studies on tetrahydrocannabinol (THC) and CBD in blood samples are, however, missing. This study aimed to investigate the relationship between THC- and CBD concentrations in blood samples among cannabis users, and to compare cannabinoid concentrations with the outcome of a clinical test of impairment (CTI) and between traffic accidents and non-accident driving under the influence of drugs (DUID)-cases. Assessment of THC- and CBD contents in cannabis seizures was also included.

METHODS

THC- and CBD concentrations in blood samples from subjects apprehended in Norway from April 2013-April 2015 were included (n=6134). A CTI result was compared with analytical findings in cases where only THC and/or CBD were detected (n=705). THC- and CBD content was measured in 41 cannabis seizures.

RESULTS

Among THC-positive blood samples, 76% also tested positive for CBD. There was a strong correlation between THC- and CBD concentrations in blood samples (Pearson's r=0.714, p<0.0005). Subjects judged as impaired by a CTI had significantly higher THC- (p<0.001) and CBD (p=0.008) concentrations compared with not impaired subjects, but after multivariate analyses, impairment could only be related to THC concentration (p=0.004). Analyzing seizures revealed THC/CBD ratios of 2:1 for hashish and 200:1 for marijuana.

CONCLUSIONS

More than ¾ of the blood samples testing positive for THC, among subjects apprehended in Norway, also tested positive for CBD, suggesting frequent consumption of high CBD cannabis products. The simultaneous presence of CBD in blood does, however, not appear to affect THC-induced impairment on a CTI. Seizure sample analysis did not reveal high potency cannabis products, and while CBD content appeared high in hashish, it was almost absent in marijuana.

Driving under the influence of non-alcohol drugs--An update. Part II: Experimental studies

Experimental studies on the impairing effects of drugs of relevance to driving-related performance published between 1998 and 2015 were reviewed. Studies with on-the-road driving, driving simulators, and performance tests were included for benzodiazepines and related drugs, cannabis, opioids, stimulants, GHB, ketamine, antihistamines, and antidepressants. The findings in these experimental studies were briefly discussed in relation to a review of epidemiological studies published recently. The studies mainly concluded that there may be a significant psychomotor impairment after using benzodiazepines or related drugs, cannabis, opioids, GHB, or ketamine. Low doses of central stimulants did not seem to cause impairment of driving behavior.

Novel psychoactive substances

There has been a significant increase in the number of new intoxicants on the illegal drugs market globally, also in Norway. The substances are given the name NPS: Novel Psychoactive Substances, and are mainly sold over the Internet. Uncertain dosage of potent substances entails a risk of accidental overdose, and therefore serious intoxication and death. In this article we provide an overview of current knowledge with regard to these substances.

Driving Under the Influence of Non-Alcohol Drugs--An Update Part I: Epidemiological Studies

Epidemiological studies of the association between drug use and involvement in road traffic crashes (RTCs) published from January 1998 to February 2015 have been reviewed. Cohort andpopulation studies compared RTC involvement among drug users and non-drug users, case-control studies compared drug use among RTC-involved and non-RTC-involved drivers, and responsibility studies and case-crossover studies were performed for RTC-involved drivers. Difficulties associated with the types of studies are discussed with a special focus on case-control studies. Statistically significant associations between drug use and RTC involvement were found for benzodiazepines and z-hypnotics in 25 out of 28 studies, for cannabis in 23 out of 36 studies, for opioids in 17 out of 25 studies, for amphetamines in 8 out of 10 studies, for cocaine in 5 out of 9 studies, and for antidepressants in 9 out of 13 studies. It was a general trend among studies that did not report significant associations between the use of these drugs and increased RTC risk that they often had either poor statistical power or poor study design compared to studies that found an association. Simultaneous use of two or more psychoactive drugs was associated with higher RTC risk. Studies on the combination of alcohol and drugs have not been reviewed in this article even though this combination is known to be associated with the highest RTC risk.

[Prevalence of injuries associated with the «russ» celebration in Norway]

BACKGROUND

Every year the Norwegian Institute of Public Health receives a number of enquiries from the media regarding the extent to which alcohol intake by upper secondary school leavers celebrating in their final spring term (the traditional Norwegian «russ» celebration) is a cause of injuries, and whether there are more injuries during this period. The purpose of this study is to investigate the prevalence of injuries in the «russ» celebration period.

MATERIAL AND METHOD

Data from the Norwegian patient register (NPR) were used to investigate the prevalence of injuries in 16-, 19- and 21-year-olds from 2007 to 2011. The 19-year-olds represent those who celebrate «russ». Injuries recorded using ICD-10 codes were examined. The month of May and the period 20 April to 20 May were compared to the other months of the year.

RESULTS

The 19-year-olds have significantly more injuries during the «russ» period compared to the 16- and 21-year-olds. In the «russ» period, the 19-year-olds accounted for 41.4% of the injuries, the 16-year-olds for 27.7% and the 21-year-olds for 30.9%. The 19-year-olds have more injuries in May compared to other months. There is a particular increase in the prevalence of head injuries.

CONCLUSION

An increase was observed in the number of injuries among 19-year-olds associated with the period of the «russ» celebration compared to the rest of the year. There are no data available which describe the causes of the injuries. There is a need for better recording of the use of alcohol or intoxicants as a possible cause. Injuries treated by the specialist health services are probably of a more serious nature, and the study may indicate an increase in serious injuries among 19-year-olds during the «russ» celebration.

Can patients receiving opioid maintenance therapy safely drive? A systematic review of epidemiological and experimental studies on driving ability with a focus on concomitant methadone or buprenorphine administration

OBJECTIVE

To perform a systematic review of the present scientific literature on the treatment with methadone or buprenorphine related to (1) traffic accident risk in epidemiological studies and (2) their effects on cognitive and psychomotor functions of relevance to driving in experimental studies.

METHODS

Searches for corresponding literature were conducted in MEDLINE, EMBASE, and PsycINFO throughout March and June of 2010. The search strategy consisted of words colligated to accident risk and culpability, in addition to cognitive and psychomotor functions of relevance to driving, all in relation to methadone or buprenorphine administration. In total, 59 studies were included.

RESULTS

Early epidemiological studies found no substantial difference in motor vehicle accident risk between methadone maintenance therapy patients (MMPs) and control groups. However, more recent studies have found an increased risk of traffic accident involvement for both MMPs and buprenorphine maintenance therapy patients (BMPs). In experimental studies, impairments of cognitive and psychomotor functions have been observed among both MMPs and BMPs when compared to control groups. When comparing MMPs with BMPs, the latter appeared to be less impaired than MMPs, but this difference may be unrelated to the maintenance therapy. Further impairments have been observed among MMPs after single doses, after an additional versus regular daily dosing, in multiple versus single dosing, and after long-term treatment compared to baseline levels. All studies showed impairments among opioid-naïve subjects after the administration of a comparatively low and single dose of either methadone or buprenorphine.

CONCLUSIONS

Both methadone and buprenorphine were confirmed as having impairing potentials in opioid-naïve subjects. At least some opioid maintenance therapy patients are observed having only slight impairments of relevance to driving. Knowing this when approaching the question of ability to drive, an individual evaluation of the driving performance, pertaining to the opioid maintained patient, may be the most useful and conclusive procedure.