Stereoselectivity of the TDxADx/FLx Amphetamine/Methamphetamine II amphetamine/methamphetamine immunoassay--response of urine specimens following nasal inhaler use.

The TDxADx/FLx Amphetamine/Methamphetamine II fluorescence polarization immunoassay (Abbott Diagnostic) for the detection of amphetamine and methamphetamine in urine was evaluated for stereoselectivity and response to specimens collected following as recommended and double the recommended dose use of Vicks Nasal Inhaler. The assay is calibrated with d-amphetamine, at cutoff concentration of 300 ng/mL for a positive response. Cross-reactivity studies demonstrated a positive result with 1000 ng/mL l-amphetamine, 300 ng/mL d-methamphetamine, and approximately 2000 ng/mL desoxyephedrine. A good correlation was observed between urines obtained following ingestion of d-amphetamine simultaneously analyzed by TDxADx/FLx Amphetamine/Methamphetamine II and gas chromatography/mass spectrometry: r2 = 0.954, N = 100. However, urine obtained following ingestion of racemic methamphetamine showed no correlation between TDxADx/FLx Amphetamine/Methamphetamine II and gas chromatography/mass spectrometry results: r2 = 0.420, N = 28. Urines collected following as recommended use for five consecutive days of Vicks Nasal Inhaler containing l-desoxyephedrine did not yield positive TDxADx/FLx Amphetamine/Methamphetamine II results. Only two urines from a subject using twice the recommended inhaler dose yielded positive TDxADx/FLx Amphetamine/Methamphetamine II results. These urines contained 1560 and 1530 ng/mL desoxyephedrine when analyzed by gas chromatography/mass spectrometry. Greater than recommended use of Vicks Nasal Inhaler may yield false positive TDxADx/FLx Amphetamine/Methamphetamine II results for amphetamine use when calibrated at 300 ng/mL d-amphetamine. If calibrated at 1000 ng/mL, d-amphetamine, the TDxADx/FLx Amphetamine/Methamphetamine II is unlikely to yield false positive results for amphetamine, even following excessive inhaler use.