At present, most DUI testing laboratories only perform tests against an established per se BAC threshold; thus limiting their ability to identify other drugs that contribute to driving impairment.

Clinical Pharmacokinetics is the study of how drugs are absorbed, distributed, metabolized and eliminated from our bodies. In this tutorial we will use a mock dataset to highlight essential considerations when conducting clinical pharmacokinetic drug-drug interaction studies (DDI studies).

THC

D-9 Tetrahydrocannabinol (THC), the primary psychoactive compound found in marijuana, enters the bloodstream when inhaled or consumed and causes impairment by binding with CB1 receptors in the brain.

THC blood concentrations don’t appear to have any direct relationship to driving performance, unlike with alcohol. This could be the result of its unique pharmacokinetics; THC diffuses through various tissues compartments.

An experienced defense attorney can dispute a THC test by asserting that its collection was conducted improperly. In New Jersey, this means it must be collected by a trained Phlebotomist or nurse in a hospital under appropriate procedures for forensic use; and must then be sent for analysis at an independent laboratory before being used as evidence against or supporting a DUI arrest.

Benzodiazepines

Benzodiazepines such as diazepam and lorazepam can be prescribed to treat insomnia, anxiety disorders, seizure disorders, anesthesia/peri-procedural sedation/skeletal muscle relaxation needs as well as pain management. Unfortunately, however, these drugs can also be abused recreationally; indeed it’s possible for individuals combining benzodiazepines with marijuana or stimulants and being charged with DUI.

Drug tests for benzodiazepines may reveal positive results, though whether or not this leads to arrest depends on various factors, including metabolism speed, tolerance level and dose frequency. Blood tests tend to be more accurate at detecting impairment as benzodiazepines remain in the body even after therapeutic dosage has been completed.

Opioids

Drug pharmacokinetics studies the absorption, distribution, metabolism, and elimination of medications by tracking observed drug concentration measurements over time. It plays an essential role in drug safety.

Clinical Pharmacokinetic Drug-Drug Interaction (DDI) studies typically present their results as mean and standard deviation (SD), however, when data do not follow a normal distribution it is preferable to present them using median and interquartile ranges instead of mean and SD. Furthermore if the study analyzes multiple probe drugs or metabolites GMR and 95% confidence intervals are also included for statistical interpretation of drug exposure changes as a whole and spaghetti plots provide visual display of this outcome summary (the figure below depicts an example concentration-time curve with and without induction of Cytochrome P450 3A).

Stimulants

Drug metabolism involves how it enters and leaves our systemic circulation system, including absorption, distribution and metabolism of drugs.

Stimulants are drugs used to speed up the brain and body, increase energy, focus attention, alertness and wakefulness and are commonly prescribed for attention deficit hyperactivity disorder (ADHD). Furthermore, stimulants have also been illegally used to enhance performance at work and school.

Psychostimulants such as amphetamine and methylphenidate are rapidly absorbed with short half-lives; however, there may be substantial interindividual variability in pharmacokinetics.

Cannabis

Cannabis is one of the world’s most commonly grown, trafficked, and used illicit drugs, cultivated, trafficked, and used illicitly. It can produce both psychological and physical side effects including euphoria, altered states of consciousness and sense of time, impaired short-term memory retention, psychomotor impairment (balance and fine motor control issues), appetite stimulation and increased risk for psychotic illness or initiating its first episode.

Use of marijuana for medical and recreational purposes has increased rapidly across many nations and is now the most commonly consumed illicit drug globally, becoming a significant public health risk.

RTI researchers conducted six double-blind clinical dosing sessions during which participants consumed THC-infused brownies or inhaled THC vapor and performed standard field sobriety tests to measure alcohol- and drug-impaired driving. Blood, urine, oral fluid pharmacokinetic data was collected along with subject self-assessments of impairment as well as horizontal gaze nystagmus evaluations.