Be aware of (R)-methamphetamine: Negative immunoassay versus positive confirmation analysis

Area of Science:

• Forensic Toxicology
• Pharmacology

Background:

• Methamphetamine, an amphetamine-type stimulant, exists as two enantiomers: (S)-methamphetamine and (R)-methamphetamine.
• (S)-methamphetamine is more potent than (R)-methamphetamine, with illicit samples often being racemic mixtures or enantiopure (S).

Purpose of the Study:

• To report cases of undetected (R)-methamphetamine consumption.
• To investigate the limitations of immunoassay screening for methamphetamine enantiomers.

Main Methods:

• Case study analysis of individuals consuming (R)-methamphetamine.
• Evaluation of immunoassay sensitivity and cross-reactivity for (S)- and (R)-methamphetamine.

Main Results:

• Two cases of confirmed (R)-methamphetamine consumption were identified.
• Both cases yielded negative results in standard immunoassay drug screening.
• Immunoassay assays demonstrated significantly higher sensitivity and cross-reactivity for (S)-methamphetamine compared to (R)-methamphetamine.

Conclusions:

• Standard immunoassay screening may fail to detect (R)-methamphetamine.
• Assay limitations stem from differential sensitivity to methamphetamine enantiomers.
• Forensic and clinical users should be aware of these limitations to avoid misinterpretation of drug test results.