Comparative study of the ratio of amphetamine to methamphetamine concentration in the urine samples of Thai patients receiving selegiline and methamphetamine abusers

The objective of this study was to compare the ratio of amphetamine to methamphetamine concentrations in urines of Thai patients receiving selegiline therapy to the ratio of amphetamine to methamphetamine concentrations in urines of Thai methamphetamine abusers. In addition, the possibility of using the ratio of amphetamine to methamphetamine to preliminarily differentiate patients receiving selegiline therapy from methamphetamine abusers was also assessed. Urine samples were collected from fifteen Thai patients (11 men and 4 women, 45-76 years old). They were outpatients of Prasat Neurological Institute and were prescribed selegiline for medical purpose. Urine samples were collected at 2, 4, 6, 8 and 20 hours after selegiline administration. The urine samples from 97 abusers were collected once from each abuser at either 2, 4, 6, 8, or 20 hours after the last methamphetamine consumption. Methamphetamine and amphetamine concentrations in urine samples were determined using solid-phase microextraction-gas chromatography-mass spectrometry. The ratio of amphetamine to methamphetamine concentrations in urines of patients receiving selegiline were significantly (p<0.01) higher than those of the methamphetamine abusers at every corresponding time point (2, 4, 6, 8 and 20 hours) after selegiline administration or methamphetamine consumption. The lowest ratio of the patients was 0.74 ± 0.07, while the highest ratio of the methamphetamine abusers was 0.41 ± 0.05 at 6 hours. The ratio of amphetamine to methamphetamine concentrations in urines could be preliminarily used to differentiate patients receiving selegiline from methamphetamine abusers with an accuracy of 84.88% when using the value ratio of 0.4 as the cut-off value.