| Objective: 1 To develop a qualitative and quantitative method for the simultaneous determination of methamphetamine and its main active metabolite amphetamine in serum and urine by GC/MS. 2 To compare the toxicokinetic profiles of methamphetamine alone with coadministration of ethanol in serum and urine. 3 To observe the changes of vital signs of rabbits preadministration and post-administration. Methods: 1 Gas Chromatography/Mass Spectrometry (GC/MS):After adding SKF525A (Internal Standard, IS), serum and urine samples were alkalized and extracted with diethyl ether, derivatized with trifluoroacetic anhydride (TFA) and processed for full-scan qualitative analysis by GC-MS, quantitative analysis by selected ion monitoring (SIM). 2 Toxicokinetic study: methamphetamine·HCl of 15mg·kg-1 was administered orally to the methamphetamine-treated group. Ethanol of 3g·kg-1 and methamphetamine·HCl of 15mg·kg-1 were administered orally to the other group. The serum and urine samples were collected before administration and at different time points after drug administration. The concentrations of methamphetamine and amphetamine were determined by GC/MS. Compartment model and toxicokinetic parameters were assessed by 3p97 program. 3 Record of vital signs: Changes of important vital signs, such as electrocardiogram, blood pressure and respiration rate , etc. were recorded during the entire experiment by BL-5 biological functional experiment system. Results: 1 The linear range for methamphetamine and amphetamine in serum and urine by GC/MS was 0.01-5.0mg·L-1 and 0.1-50mg·L-1 , respectively. The limit of detection was 0.005mg·L-1. The overall extraction recoveries of the analytes in serum and urine were more than 72% ; The analytical recovery was 92.07 –102.05 %; The inter-and intra-day relative standard deviation of precisions were less than 10.0 %. 2 The mean serum concentration-time profile of methamphetamine after oral administration to rabbits was fitted to a two-compartment open model with first order kinetics and not affected by in combination with ethanol. The main toxicokinetic parameters of methamphetamine administered alone and in combination with ethanol were as follows: Cmax was 1.457±0.094 mg·L-1 versus 1.648±0.127 mg·L-1, Tmax was 1.557±0.078h versus 1.148±0.034h , t1/2(ka) was 0.384±0.052h versus 0.179±0.028h, Ka was 1.746±0.238h-1 versus 3.647±0.519 h-1, αwas 0.746±0.146 h-1 versus 0.913 ±0.138 h-1, βwas 0.234±0.037 h-1 versus 0.245±0.036 h-1, CL was 1.769±0.114L·h-1·kg-1 versus 1.674±0.160L·h-1·kg-1 , V/F was 8.912±0.446L·kg-1 versus 9.302±0.646L·kg-1, AUC was 16.188±0.528 mg·h·L-1 versus 16.919±0.911mg·h·L-1. 3 After oral administration, intermittent trembles appeared in limbs, blood pressure increased, respiration frequency and heart rate accelerated and peaked at 1 h or so, then descended slowly. Conclusions: 1 It was the first time to establish a GC/MS method for the simultaneous determination of methamphetamine and its principle metabolite amphetamine in biological matrices. The method proved to be simple, sensitive and reproducible and could be applied to analyse intoxication and abuse cases of methamphetamine rapidly. 2 Ethanol can accelerate the absorption of methamphetamine(p<0.05) and show little effect on the elimination of methamphetamine. Because ethanol can increase the toxicity of methamphetamine, it is suggested that interactions of the two drugs should be considered for the identification of ethanol and methamphetamine abuse. 3 It provides the theoretical basis for forensic evaluation of reasonable specimen collections , combined abuse of ethanol and methamphetamine and inferring poison dose of methamphetamine as well as poison time.
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