Immunoassay-based detection of fentanyl analogs in forensic toxicology

PurposeThe abuse of fentanyl and its analogs (fentalogs) is of growing concern globally. Forensic toxicology laboratories must detect these emerging drugs in biological evidence, and immunoassay is the most widely used screening technique. In this study, the cross-reactivity of 13 fentalogs were investigated using five commercially available kits.MethodsDose-response curves were generated using six N-acyl-substituted fentalogs (4-ANPP, acetylfentanyl, butyrylfentanyl, furanylfentanyl, isobutyrylfentanyl, valerylfentanyl), one desphenethyl fentalog (norfentanyl), two piperidine-modified [(+)-cis-3-methylfentanyl, carfentanil], and four phenethyl and piperidine substituted fentalogs (alfentanil, norcarfentanil, remifentanil, sufentanil). Cross-reactivities were estimated for each assay to determine its overall effectiveness for fentalog screening in toxicological samples.Results and conclusionsSeveral commercial assays were able to detect either N-acyl or piperidine-modified fentalogs, but none was capable of detecting both. Although this is an inherent disadvantage of the immunoassay approach, it arises from the diverse structural nature of the fentanyl analogs themselves.