Summary

• During a validation study, risperidone and its active metabolite, 9-hydroxy-risperidone (paliperidone), were found to cross-react with the DRI^® fentanyl immunoassay. The authors concluded that a similar chemical moiety (3-methyl-5-piperidino-2-pentene) that is shared with fentanyl and acetylfentanyl may be recognized by the antibody for the immunoassay. However, since the highest concentrations of risperidone and 9-hydroxy-risperidone measured in the patient sample were 2701 ng/mL and 3043 ng/mL, respectively, and cross-reactivity was only observed starting at concentrations of 3500 ng/mL and 12,500 ng/mL, respectively, other risperidone metabolites may also be involved.¹
  • The authors call for confirmatory testing to be performed for all positive samples to determine if the sample contains fentanyl, acetylfentanyl or is a false positive.

CLINICAL STUDIES

Immunoassay

Wang et al (2014)¹ conducted a 4-month study to validate the use of an automated DRI fentanyl immunoassay for urine drug screening and determine the potential cross-reactivity of acetylfentanyl and other pharmaceuticals.

Study Design/Methods

Urine toxicology that screened positive via the DRI fentanyl immunoassay were analyzed using liquid chromatography-high resolution mass spectrometry (LC-HRMS) for fentanyl, fentanyl analogs, and 200+ drugs (illicit and pharmaceutical agents) plus their respective metabolites. A quantitative liquid chromatography-tandem mass spectrometry (LC-MS-MS) method for fentanyl, norfentanyl, acetylfentanyl, risperidone and 9-hydroxy-risperidone was utilized for urines that screened positive for fentanyl (n=36) along with fentanyl-negative samples collected during the same time period. Cross-reactivity was analyzed by spiking standards of each compound in drug-free urine at increasing concentrations and testing them in the same manner as the patient samples.

Results

Of the 1269 urine samples sent from the ER to be analyzed, 36 (3%) screened positive using the DRI fentanyl immunoassay. Of the 36 positive samples, the LC-HRMS method confirmed 29 positive samples for fentanyl and 7 false positives. Risperidone and 9-hydroxy-risperidone were detected in 5 of the 7 false positives in addition to 3 additional urine samples that also contained fentanyl. Acetylfentanyl, acetyl norfentanyl and other fentanyl analogs were not detected in any of the 36 samples. Further analysis of the 36 positive screens via the quantitative LC-MS-MS method correlated with the LC-HRMS qualitative Results. The overall diagnostic sensitivity and specificity of the DRI fentanyl immunoassay was 100% and 86%, respectively. Spiking studies revealed that acetylfentanyl, risperidone and 9-hydroxy-risperidone showed cross-reactivity starting at 2.5 ng/mL, 3500 ng/mL and 12,500 ng/mL, respectively, resulting in cross-reactivity of 80%, 0.05% and 0.01%, respectively.

Authors’ Conclusions

The authors concluded that the DRI fentanyl immunoassay can be used to screen for fentanyl and acetylfentanyl but call for confirmatory testing to be performed for all positive samples to determine if the sample contains fentanyl, acetylfentanyl or is a false positive. The authors also noted that risperidone and its active metabolite, 9-hydroxy-risperidone, were found to cross-react with the DRI fentanyl immunoassay partly due to a similar chemical moiety (3-methyl-5-piperidino-2-pentene) that is shared with fentanyl and acetylfentanyl and may be recognized by the antibody for the immunoassay. However, since the highest concentrations of risperidone and 9-hydroxy-risperidone measured in the patient sample were 2701 ng/mL and 3043 ng/mL, respectively, and cross-reactivity was only observed starting at concentrations of 3500 ng/mL and 12,500 ng/mL, respectively, other risperidone metabolites may also be involved.

LITERATURE SEARCH

A literature search of Ovid MEDLINE^®, Embase^®, BIOSIS Previews^®, and Derwent Drug File databases (and/or other resources, including internal/external databases) pertaining to this topic was conducted on 17 September 2024.