Urinary excretion of amphetamine after termination of drug abuse

Important issues in urinary drug testing are the variability between consecutive urine specimens, the duration of positive specimens after last intake, and the usefulness of creatinine concentration to correct for variability in urine concentration. These issues were addressed in the present study with amphetamine as the drug of abuse. Drug users who were starting their sentences in prison participated in the study. Urine specimens were collected 1 to 5 times per day. Screening was performed by EMIT d.a.u. (cutoff, 0.30 microgram/mL) and EMIT II (cutoff, 1.00 microgram/mL), and confirmation was performed with gas chromatography-mass spectrometry. Creatinine and pH were recorded. Amphetamine was demonstrated in seven subjects. The highest concentration was 135 micrograms/mL. The last positive-screened specimen was observed by EMIT d.a.u. after almost 9 days of imprisonment and by EMIT II after 3 days. Large concentration differences could be found between consecutive specimens, accompanied by considerable differences in creatinine and pH. The individual curves were generally smoother after creatinine correction of concentrations. As expected, urinary pH was observed to influence the excretion.