Detection of 58 fentanyl analogs using ARK fentanyl II and Immunalysis fentanyl immunoassays

The ability to detect fentanyl analogs in urine aids in patient management. Little is published about the new ARK™ Fentanyl II Assay formulation's ability to detect fentanyl analogs. Norfentanyl (fentanyl metabolite) cross-reactivity with the ARK II assays is 7%, while the Immunalysis SEFRIA assay norfentanyl cross-reactivity is approximately 0.005%. The purpose of this study was to determine the new ARK II and SEFRIA fentanyl assays' detection of 58 fentanyl analogs.

Drug-free urine was fortified with 0-100 ng/mL (0-0.297 µmol/L) of the fentanyl analog and analyzed using the previously evaluated immunoassays. Results were compared to molecular structure. Of the 58 analogs tested at ≤ 100 ng/mL (0-0.297 µmol/L), the ARK II and SEFRIA assays produced 51 and 57 positive results respectively. The cross-reactivity of the assay was predominantly determined by the location of the modification. Most modifications to the aniline ring and/or amide group did not affect the ARK II or SEFRIA assay. Modifications to the piperidine ring decreased detection by ARK II assay. Of the 7 compounds which were undetected by the ARK II assay, all had modifications to the N-alkyl chain. Norsufentanil was not detected by either assay and was the only analog not detected by the SEFRIA assay.

The ARK II and Immunalysis fentanyl immunoassays can detect a range of fentanyl analogs with acryl, butyryl, or furanyl modifications to the amide group or aniline ring of the molecule. N-alkyl chain and piperidine ring modifications significantly affect the ARK II assay's ability to detect the analogs, while the SEFRIA assay appeared less affected and detected all analogs tested except for norsufentanil, which was also not detected by the ARK II assay.