blood and the brain, its site of action. It is metabolized in simple ways, has no active metabolites, and is not bound to plasma proteins. No other drug has all of these char- acteristics. Instead, drugs of abuse have more complex and variable paterns of absorption, distribution, metabolism and excretion, and behavioral effects that are not closely cor- related with blood concentrations. Tird, when considering drugged driving
There are hundreds of potentially impairing drugs that are now in widespread use, with the potential for virtually unlimited additional synthetic drugs in the future.
today, we oſten deal with multiple drugs in a single driver. Tere are hundreds of potentially impairing drugs that are now in widespread use, with the potential for vir- tually unlimited additional synthetic drugs in the future. Furthermore, an endless combination of drugs, with and without alcohol, creates a complexity that no blood concentration determination can unravel. A simple example makes this case with
unmistakable clarity. Nonmedical use of opioids—from heroin to methadone—is an increasing problem in the United States.4 Tolerance plays a critical role in the level of impairment caused by these drugs. Te consumption of 50 mg of methadone by a person who has not used opioids in a week or more can be lethal. Death is the ultimate impairment! However, with chronic ad- ministration of methadone at stable doses, typically no sedation or measurable impair- ment is produced, even with doses several times this level. Tolerance is typical of most psychotropic drugs and to a somewhat lesser extent with alcohol. Now assume that sophisticated new
research is done to find a blood concentra- tion of methadone that is the equivalent to the 0.08 g/dL BAC—the presumption of “impairment.” Tere is no test yet devised for tolerance that can be used in a law enforcement context and no breath, blood, urine or other drug test for tolerance. Tese facts produce an unsolvable dilemma. Set a low blood concentration for methadone in blood that is appropriate for drug-naïve driv- ers and you define all unimpaired-tolerant drivers as impaired. Set the blood concentra-
38 datia focus
tion high enough to identify the impaired drug-tolerant drivers and you miss all the impaired drivers who lack opioid tolerance. Fourth, with drugs the blood concentra-
tions do not correlate well with impairment concentrations because many drugs are rapidly cleared from the blood but sustain impairing effects for longer periods of time. Tis problem is compounded by the fact that blood samples from drivers are typi- cally taken hours aſter an incident, meaning that the blood concentration at the time of collection is far lower than the concentra- tion at the time of arrest, when the arrestee was actually driving. As if that were not enough, drug users undergoing withdrawal (i.e. aſter the drug is gone from the brain) are oſten impaired because of the with- drawal syndrome, even though their blood drug concentrations are negligible or zero. Today the common focus of the search for a 0.08 g/dL BAC equivalent is mari- juana. Marijuana is similar to other drugs of abuse because many marijuana users are impaired at low blood concentrations of its psychoactive components, delta-9-tetra- hydrocannabinol (THC) and its metabo- lites. Marijuana advocates want to use an impairment standard of 5 ng/mL of THC in blood claiming that it is the equivalent of the 0.08 g/dL BAC. Tey assert that they want to use this standard to stop marijuana- impaired driving. It is not surprising that they support this approach because it gives them cover for promoting marijuana use, while this standard actually guts efforts to reduce marijuana-impaired driving. How? Because this high concentration of THC is seldom found among drivers arrested for impairment. A large study of drivers arrested for drugged driving in Sweden (i.e. drivers arrested because law enforce- ment officers determined that they were impaired) showed that among drivers posi- tive for marijuana tested between 30 and 90 minutes aſter arrest, over 90 percent had THC concentrations under 5 ng/mL, 61 percent had THC concentrations below 2
winter 2013
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