Duration of detectable methamphetamine and amphetamine excretion in urine after controlled oral administration of methamphetamine to humans

Background: Confirmation of a workplace drug test requires urinary methamphetamine (MAMP) and amphetamine (AMP) concentrations ≥500 and 200 μg/L, respectively, but cutoffs at half those values (250/100 μg/L) have been proposed. We determined the urinary excretion of MAMP after oral ingestion and examined the effect of using lower cutoffs on detection of exposure. Methods: Volunteers (n = 8) ingested four 10-mg doses of MAMP · HCl daily over 7 days, and five of them ingested four 20-mg doses 4 weeks later. After ingestion, the volunteers collected all urine specimens for 2 weeks. After solid-phase extraction, MAMP and AMP were measured by gas chromatography-positive chemical ionization mass spectrometry with dual silyl derivatization. Results: MAMP and AMP were generally detected in the first or second void (0.7-11.3 h) collected after drug administration, with concentrations of 82-1827 and 12-180 μg/L, respectively. Peak MAMP concentrations (1871-6004 μg/L) after single doses occurred within 1.5-60 h. MAMP ≥500 μg/L was first detected in the first or second void (1-11 h) at 524-1871 μg/L. Lowering the MAMP cutoff to 250 μg/L changed the initial detection time little. AMP ≥200 μg/L was first detected in the 2nd-13th (7-20 h) post-administration voids. At a cutoff of 100 μg/L, AMP was first confirmed in the second to eighth void (4-13 h). Reducing the cutoff to 250/100 μg/L extended terminal MAMP detection by up to 24 h, increased total detection time by up to 34 h, and increased the total number of positive specimens by 48%. Conclusions: At the lower cutoff, initial detection times are earlier, detection windows are longer, and confirmation rates are increased. Elimination of the AMP requirement would increase detection rates and allow earlier detection.