A Comparison of High Drug Concentrations in Impaired Driving and Postmortem Casework in Harris County, TX.
Drug-impaired driving is a growing public safety issue. Addressing impairment due to drugs other than ethanol can be challenging for forensic toxicologists as many factors need to be considered including the type of drug(s), drug-drug interaction, the dose(s) and the individuals physiological condition and drug use history. Interpretation of blood drug test results is additionally difficult as drug concentrations in impaired driving cases may overlap levels typically viewed as toxic. This study compares blood concentrations of drugs in impaired driving cases to those in postmortem cases in Houston, TX, from 2014 to 2020. Blood drug concentrations from driving while intoxicated (DWI) or driving under the influence of drugs (DUID) cases submitted to Houston Forensic Science Center (HFSC) and Harris County Institute of Forensic Sciences (HCIFS) were compared to postmortem blood test results from HCIFS. Eight DWIDUID cases had drugs that exceeded impaired driving concentrations reported in the literature. These drugs included fentanyl (220 ngmL), oxycodone (680 ngmL), hydrocodone (310 and 490 ngmL), clonazepam (330 ngmL), methamphetamine (3,500 and 7,100 ngmL) and tetrahydrocannabinol (THC) (160 ngmL). For oxycodone and hydrocodone, the presented DWIDUID cases exceeded 91% and 96% of postmortem concentrations, respectively. The 7,100 ngmL methamphetamine DWIDUID result was greater than 98% of postmortem cases. The presented DWIDUID concentrations were higher than all but one postmortem case for clonazepam and higher than all postmortem cases for THC. This study demonstrates that extremely high drug concentrations in DWIDUID casework blur the line between therapeuticrecreational and toxic concentrations.