Stock Car Science

C’mon, will Chad Knaus please push the limits of the gray area so that I can write about something other than drugs? But that’s the big news (again) this week given that someone leaked that the drug Jeremy Mayfield tested positive for was methamphetamine.

Amphetamine (C₉H₁₃N) is a psychostimulant. Methamphetamine (C₁₀H₁₅N) is an even more powerful psychostimulant. Standard tests usually test for the general class of amphetamines (which includes meth). For example, the Federal government guidelines require that companies requiring commercial class drivers licenses clear their employees for the “SAMHSA-5″ the Substance Abuse and Mental Health Services Administration. So most drug testing companies’ basic test covers:

1. Cannabinoids (marijuana, hash)
2. Cocaine (cocaine, crack, benzoylecognine)
3. Amphetamines (amphetamines, methamphetamines, speed)
4. Opiates (heroin, opium, codeine, morphine)
5. Phencyclidine (PCP)

A lot of the amphetamine molecules look very similar to neurotransmitter molecules that occur naturally in your body, like epinephrine, norepinephrine, and dopamine. Methamphetamine and amphetamine have an interesting property: They have enantiomers. Long word, but don’t panic. Put your right and left hands in front of you backs of your hands toward your face. They are mirror images of each other. There’s no way that you can rotate your hands so that they line up exactly on top of each other (meaning that both backs still face you). Meth is the same way. There are two versions of it.

l-methamphetamine (an abbreviation for levomethamphetamine) is on the right in the picture above. l-meth is the active ingredient in inhalers like Vicks. (This is why Mayfield was asked specifically if he had used Vicks. The other form dextromethamphetamine or d-methamphetamine is what we know as meth.

When methamphetamine gets to the brain,it triggers the release of of dopamine, serotonin and norepinephrine, the feel-good neurotransmitters, which is why it induces such a powerful feeling of euphoria – and why it is so highly addictive. Meth is often smoked because you get more of the feel-good molecules into your body that way (90.3% bioactive via smoking vs. 60.2% orally).

Here’s why the presence of two versions of the same molecule is important: If you take meth, it’s entirely d-methamphetamine. A number of other drugs contain molecules like pseudoephedrine, which are metabolized by the body and can produce amphetamine.

For example, famprofazone, an over-the-counter med that’s found in some pain medications, produces equal amounts of the d- and l- forms of meth and amphetamine when it is metabolized in the body. So if the meth that is detected is due to use of this drug, then there should be comparable amounts of each version of the molecule.

The use of something like Adderall or Claritin-D that could produce amphetamines in the urine as a byproduct would produce both types of molecules, which leads me to wonder whether the reason Dr. Black said that there was “no way” the combination of the two over-the-counter medicines could have produced the result they saw is because they detected only the d- version of amphetamine molecules and the over-the-counter medications would have produced both l- and d- versions. (And if you used Vick’s, you’d find only the l-version.

Needless to say, tests beyond the basic five are required to detect the enantiomers. The two molecules have the same mass - they’re just shaped differently. The shape means that they attach to other molecules differently, so you can distinguish between them by seeing how they react to other molecules. Current tests are very sensitive, allowing testers to rule out prescription drugs as the source of the positive results.

More as it develops, but I really am making a plea to Chad to come up with something really creative so that the next entry is about racecars and not this.