Stability of synthetic cathinones in clinical and forensic toxicological analysis - where are we now?

Understanding the stability of analyzed drugs in biological samples is a crucial part for an appropriate interpretation of the analytical findings. Synthetic cathinones, as psychoactive stimulants, belong to a major class of new psychoactive substances. Since they are subject to several degradation pathways, they are known to clinical and forensic toxicologists as unstable analytes in biological samples. When interpreting analytical data of synthetic cathinones in biological samples, analysts must be aware that concentration of analytes may not accurately reflect the levels at the time they were acquired due to many factors. This review provides (i) an overview of the current scientific knowledge on the stability of synthetic cathinones and/or metabolites in various human biological samples with a focus on factors that may deteriorate their stability - such as storage temperature, length of storage, matrix, pH, type of preservatives, concentration of analytes and the chemistry of the analytes - and (ii) possible solutions on how to avoid such degradation. The PubMed database as well as Google Scholar was thoroughly searched to find published studies on the stability of synthetic cathinones since 2007 by searching specific keywords. A total of 23 articles met the inclusion criteria and were included in this review. Synthetic cathinones that carry methylenedioxy or N-pyrrolidine ring showed higher degradation resistance over other substituted groups. Acidification of samples pH plays a crucial role at increasing the stability of cathinones even with analytes that were frequently considered as poorly stable. This review also provides several recommendations for best practice in planning the experimental design, preservation and storage conditions in order to minimize synthetic cathinones' degradation in human biological samples.