Cytisine is the active ingredient in preparations used for smoking cessation. Its popularity is attributed to its low cost, efficacy, and low incidence of adverse effects. Additionally, its easy over-the-counter availability is also significant. This accessibility makes it a potential substance for use in suicidal attempts. The aim of this study was to develop a method for the determination of cytisine in biological material for use in clinical and forensic toxicology, and to apply this method in authentic cases. Biological samples were subjected to liquid-liquid extraction using cytisine-d4 as an internal standard. Analyses were performed using a Hydrophilic Interaction Liquid Chromatography (HILIC) column with the technique of ultra-high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry. For both matrices (blood and urine), the linear concentration range was 5-1000ng/mL. The method met all validation requirements. The concentration of cytisine in a man taking it for smoking cessation in post-mortem materials was 21.4ng/mL in blood, 958.9ng/mL in urine, ca. 30ng/mL in vitreous humor, and ca. 40ng/mL in bile. In contrast, for a man with cytisine intoxication, the concentration was 174.6ng/mL in blood and > 10,000ng/mL in urine. In both cases, no N-methylcytisine was detected. The developed method can be used for the determination of cytisine in post-mortem biological matrices as well as for clinical purpose. We presented the concentrations of cytisine in the post-mortem biological samples of a man taking cytisine for smoking cessation and of a man with suicidal cytisine poisoning.
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