Issues When Measuring Drug Toxicity

WIS has highlighted key points in this article.

 

This column is the corollary to my earlier story: Problems with measuring drug toxicity. An important issue which arises from the biological samples taken by a drug recognition expert (DRE) involves s. 254(3.4(a)(b) and (3.6) of the Criminal Code where they read as follows:

“(3.4) If, on completion of the evaluation, the evaluating officer has reasonable grounds to believe that the person’s ability to operate a motor vehicle, a vessel, an aircraft or railway equipment is impaired by a drug or by a combination of alcohol and a drug, the evaluating officer may, by demand made as soon as practicable, require the person to provide, as soon as practicable, (a) a sample of either oral fluid or urine that, in the evaluating officer’s opinion, will enable a proper analysis to be made to determine whether the person has a drug in their body; or (b) samples of blood that, in the opinion of the qualified medical practitioner or qualified technician taking the samples, will enable a proper analysis to be made to determine whether the person has a drug in their body.

“(3.6) If the analysis of a sample provided under paragraph (3.4)(b) demonstrates that the person has a drug in their body that is of a type that the evaluating officer has identified as impairing the person’s ability to operate a motor vehicle, vessel, aircraft or railway equipment, that drug — or, if the person has also consumed alcohol, the combination of alcohol and that drug - is presumed, in the absence of evidence to the contrary, to be the drug, or the combination of alcohol and that drug, that was present in the person’s body at the time when the person operated the motor vehicle, vessel, aircraft or railway equipment and, on proof of the person’s impairment, to have been the cause of that impairment, the drug recognition evaluator (DRE) makes the demand for the collection of a biological sample: oral fluid, urine, or blood.”

The implication from these sections is that these three sample types are equivalent as indicators to support or refute the DRE officer’s opinion regarding impairment. This is untrue, according to Dr. James Watterson, professor and chair in the department of forensic science at Laurentian University. Watterson says that “the amount of the drug in the body opens up to a great deal of misconceptions.”

The detection of a drug or one of its key metabolites in urine is only an indication of prior exposure to that drug and provides no indication as to whether the subject is impaired. The implied time window over which exposure may have occurred is dependent on both the individual and the drug but can be days. Indeed, drugs or, more often, metabolites may be detectable in urine after they are not detectable in blood or after they are no longer exerting any effects.

Drug detection in oral fluid is more indicative of the presence of drugs in circulating blood at the time of sample collection, but correlation of oral fluid drug concentrations with corresponding drug concentrations is variable between individuals. Further, some drugs act to cause dry mouth,impeding oral fluid production and collection. Finally, the route by which some drugs are consumed may “contaminate” the oral fluid. For example, smoking cannabis results in high oralfluid cannabinoid concentrations.

However, this is primarily due to contact between the smoke and inside of the mouth, as opposed to arising due to the presence of cannabinoids in the bloodstream. The influence of oral fluid contamination by residual cannabinoids in the mouth from ingesting edible cannabis products is unknown at present.

 

What is of real concern is: As a society, what are we willing to accept as a drug concentration in the blood of drivers? Individuals will often say that they may be perfectly fine following some substance use, but often may be underestimating their degree of impairment.

 

The challenge is that unlike alcohol which does not have any normal, accepted medical uses from 100 years ago, THC does as it is used for therapeutic use in various medical conditions, including treating seizures, chronic pain and post-traumatic stress disorder.

 

Importantly, a number of drugs used to treat these conditions can be impairing with respect to driving in subjects comparatively naïve to the effects of those drugs. Further, for each medical condition, it must be considered whether an untreated individual (i.e., drug free) is more or less impaired with respect to driving than that person would be after consuming their prescribed dose of the drug. The new cannabis legislation presents new dilemmas for the government which will seriously impact Canadians.