Methamphetamine d- and l- isomer Testing Basics

Many prescription and illicit drugs exist in two molecular forms, known as stereoisomers, or chemical mirror images. Think of the way your left and right hands mirror each other when you press your palms together. However, if you place your right palm over the top of your left hand, you notice they are in fact different. Same is true with stereoisomer molecules. While they appear to be the same molecule, and have the same chemical formula and similar chemical properties, they are actually different compounds, and may vary in their effect on the body.

Methamphetamine is a stereoisomer drug and is available in two forms: d- and l-. The d- form is most frequently used as a prescription stimulant and appetite suppressant. The l- form is available over-the-counter as the active ingredient of the Vicks inhaler and is a metabolite of certain prescription medications. Illegally produced methamphetamine may contain mixtures of both isomers, with a substantially higher amount of d-methamphetamine present than most commercial products.   Both, d- and l- forms will register a positive methamphetamine result by both immunoassay and PremierTox UPLC/MS/MS.

In order to help clinicians determine whether a positive test for methamphetamine may be due to an illicit source, PremierTox performs an additional analysis, which reports the percentage of d- isomer in a specimen. Because of manufacturing impurities and normal body metabolism, laboratory industry guidelines have been established to allow for trace presence of the d- isomer, even though 100% l- isomer is expected with non-illicit use. Typically, providers can interpret a report that indicates more than 80% l-methamphetamine, to be consistent with the inhaler medicine or non-illicit use.

If, however, the PremierTox isomer report reveals more than 20% d-methamphetamine present, the result indicates the possibility of illicit methamphetamine use.  This result may warrant a more introspective discussion with the patient regarding potential illicit use of prescription or illegally produced methamphetamine.

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