Methamphetamine and amphetamine pharmacokinetics in oral fluid and plasma after controlled oral methamphetamine administration to human volunteers

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 μg/L (10 mg) and 26.2-44.3 μg/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 μg/L (10 mg) and 75.3-321.7 μg/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 μg/L for up to 24 h in 9 of 12 individuals (mean, 7.3 ± 5.5 μg/L at 24 h); in oral fluid the detection window was at least 24 h (mean, 18.8 ± 18.0 μg/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.