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Schepers RJ, Oyler JM, Joseph RE, Cone EJ, Moolchan ET, Huestis MA. 
“Methamphetamine and amphetamine pharmacokinetics in oral fluid and plasma after controlled oral methamphetamine administration to human volunteers”. 
Clin Chem. 2003 Jan 31;49(1):121-32.

BACKGROUND: Methamphetamine (METH) and amphetamine (AMP) concentrations in 200 plasma and 590 oral fluid specimens were used to evaluate METH pharmacokinetics and pharmacodynamics after oral administration of sustained-release METH.

METHODS: Eight participants received four oral 10-mg S-(+)-METH hydrochloride sustained-release tablets within 7 days. Three weeks later, five participants received four oral 20-mg doses. Blood samples were collected for up to 24 h and oral fluid for up to 72 h after drug administration.

RESULTS: After the first oral dose, initial plasma METH detection was within 0.25-2 h; c(max) was 14.5-33.8 micro g/L (10 mg) and 26.2-44.3 micro g/L (20 mg) within 2-12 h. In oral fluid, METH was detected as early as 0.08-2 h; c(max) was 24.7-312.2 micro g/L (10 mg) and 75.3-321.7 micro g/L (20 mg) and occurred at 2-12 h. The median oral fluid-plasma METH concentration ratio was 2.0 across 24 h and was highly variable. Neutral cotton swab collection yielded significantly higher METH and AMP concentrations than citric acid candy-stimulated expectoration. Mean (SD) areas under the curve for AMP were 21% +/- 25% and 24% +/- 11% of those observed for METH in plasma and oral fluid, respectively. After a single low or high dose, plasma METH was >2.5 micro g/L for up to 24 h in 9 of 12 individuals (mean, 7.3 +/- 5.5 micro g/L at 24 h); in oral fluid the detection window was at least 24 h (mean, 18.8 +/- 18.0 micro g/L at 24 h). The plasma and oral fluid 24-h METH detection rates were 54% and 60%, respectively. After four administrations, METH was measurable for 36-72 h (mean, 58.3 +/- 14.5 h). CONCLUSIONS: Perceived advantages of oral fluid for verifying METH exposure compared with urine include simpler specimen collection and reduced potential for adulteration, but urine offers higher analyte concentrations and a greater window of detection.
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