LAUSR

Phenyltetrahydroimidazothiazole (PTHIT, tetramisole) ist the most frequently used adulterant of cocaine and exists in the two enantiomeric forms levamsiole (S) and dexamisole (R). Existing studies show diverse fractions of samples containing enantiopure levamsiole, levamisole-enriched mixtures and racemic tetramisole as adulterant. However, blood samples have never been enantioselectively tested for PTHIT. Since enantiomers are usually metabolized stereoselectively, chiral analysis of blood samples can help estimate the time of drug use, provided that a racemic substance is ingested. Therefore, an enantioselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed using a chiral column. Validation of the method was carried out for methanolic substance samples as well as serum samples and showed satisfactory selectivity, sensitivity, linearity (0.05-100 ng/mL), precision and accuracy. 151 cocaine samples seized in Germany between 2018-2021 were analyzed. Most (94 %, n = 48) of the 51 PTHIT-positive samples contained racemic tetramsiole, while there were two samples containing levamisole-enriched mixtures and one sample containing nearly enantiopure levamisole. Furthermore, 157 cocaine and/or benzoylecgonine-positive forensic serum samples were tested with cocaine-positive samples showing the highest frequency of PTHIT-detection (43 %). All positive samples contained either dexamisole alone or (R)/(S)-concentration ratios >1 (1.05-70.6). Finally, a self-administration study was conducted with 3 subjects taking 10 mg of racemic tetramisole each. While peak concentrations and corresponding times did not differ significantly between the enantiomers, dexamisole showed significantly longer apparent elimination half-lives (7.02-10.0 h) than levamisole (2.87-4.77 h). The resulting steadily increasing (R)/(S)-ratios can therefore be helpful in estimating the time of cocaine consumption.