In a Driving Under the Influence of Drugs (DUID) case there are many questions that the government has to answer in order for there to be a conviction. One of the most important questions that the government likes to frame the case in is whether or not there is impairment? This is the incorrect question, the properly stated question is whether or not the government can with the information provided and presuming nothing can validly conclude impairment for a specific limited purpose, meaning safely driving an automobile?

Impairment is a tricky concept when it comes to drugs.

We have blogged before here on a six part post on Phar­ma­col­ogy. Our posts focued on the fol­low­ing top­ics:
Part 1. Intro­duc­tion
Part 2. Phar­ma­co­ki­net­ics
Part 3. Phar­ma­co­dy­nam­ics
Part 4. Bioavail­abilty
Part 5. “Free ver­sus Bound Drug“
Part 6. Elu­ci­dat­ing Phar­ma­co­dy­namic Effect from an Ana­lyt­i­cal Chem­istry Result

In a DUID case, the laboratory is asked to test the blood. The question is: “For what?” Whether it is GC-MS or LC-MS, there is no universal method that will detect and quantify for all drugs of abuse. The typical work flow and method of analysis in a crime laboratory can be described thusly:

The approved methods for analysis are one or more types of immunoassay (IA) screens, confirmed by gas chromatography and mass spectrometry (GC/MS). These IA tests as screening tests are designed to be qucik and easy to use providing for a high rate of false positives and some false negatives. If you test below the drug cutoff levels on the initial screens, the lab does not report it as positive or continue with the confirmatory tests. This can be an issue in the case of a false negative as we will discus below. If you test above the cutoff on the initial screens, but below them on the confirmatory test, the lab may or may not still report it as positive and quantify it.

Speaking from strictly a pharmacology point of view and not from a legal probable cause to test/search point of view, it is best practice to test for everything. The reason being that there may be drugs whose presence in their free form may, in combination with the detected analyte, compete for certain receptors and may compete for elimination. If you only look for one specific drug and miss the other drug that may have an antagonistic effect, then you may incorrectly conclude possible impairment when in fact when globally examined with a broader scope search, there is no likely pharmacodynamic effect or that not valid conclusion can be drawn based upon the data and the lack of information.

This is something that we should keep in mind when litigating these cases. If the laboratory does a very limited search using LC-MS or GC-MS using a particular column that only is useful for discovering barbiturates, for example, then it will likely be no good at separating/detecting properly and validly for drugs that have antagonistic effects that may compete or supersede the effects of the discovered barbiturate.

This is a major problem in modern testing.

How can there be a valid call of possible impairment if you haven’t eliminated a potential legitimate source of non-impairment, namely a drug in a sufficient quantity that has an antagonistic effect?

So, the question becomes what did they test for and did they test for drugs that provide antagonistic effects?

Only in the bizarre world of law can lack of testing for the antithesis prove the thesis.