Interference of the novel designer benzodiazepine 4'-chloro deschloroalprazolam with alprazolam analysis in toxicology and seized drug DUID casework.

In recent years, the emergence of the novel designer benzodiazepine 4'-chloro deschloroalprazolam has presented a new challenge for forensic laboratories by interfering with the identification and quantitation of alprazolam. As an isomer of alprazolam, 4'-chloro deschloroalprazolam has similar physicochemical properties and can be misidentified in casework samples as alprazolam without a specific method to differentiate the two analytes. Starting in late 2021, the Houston Forensic Science Center (HFSC) received toxicological and seized drug evidence indicating the presence of 4'-chloro deschloroalprazolam. An interference study was performed to supplement the laboratory's validated benzodiazepines method for toxicological samples to differentiate alprazolam from 4'-chloro deschloroalprazolam. This study showed that while the isomers could not be chromatographically resolved using the current method, they could be differentiated based on their retention times relative to the internal standard, alprazolam-d5. Based on these findings, the HFSC toxicology laboratory reports test results as "unsuitable for analysis due to an interference" if a suspected alprazolam peak elutes before the alprazolam-d5 peak, even if all identification and quantification criteria (e.g., retention time) were acceptable. Additionally, the seized drug and toxicology laboratories re-evaluated previously analyzed alprazolam-positive casework to determine if suspected 4'-chloro deschloroalprazolam had been misidentified as alprazolam. This report presents three cases: one case with toxicological evidence indicating the presence of both 4'-chloro deschloroalprazolam and alprazolam, and two cases with both seized drug material and toxicology evidence indicating the presence of 4'chloro deschloroalprazolam with no detected alprazolam.