Evaluation of nitazene immunoassay test strips for rapid in-situ detection of nitazene and nitazene analogs in illicit drug samples.

Background: The detection of nitazene compounds in the United Kingdom has raised concerns among healthcare professionals, public health authorities, and law enforcement due to the increased risk of fatal overdose, particularly among opioid users. In response, nitazene testing strips have been distributed to help users identify these substances in drugs they may consume. However, to date, limited testing has been conducted on the effectiveness of these strips.

Methods: This study assesses the sensitivity and selectivity of a widely distributed nitazene immunoassay drug testing strip. The limit of detection and selectivity was examined for 36 nitazene analogs and 93 other drugs and cutting agents commonly encountered in illicit samples. The effectiveness of the test strips for the detection of metonitazene in the presence of other drugs was examined using a series of concentrations in solution in combination with other drugs. Testing of the strips was also carried out using authentic seized heroin samples.

Results: The strips detected 28 out of 36 nitazene compounds (78%) with detection limits ranging from 250 ng/mL to 100 µg/mL. The strips did not provide positive results for 93 other drugs and cutting agents at a concentration of 100 µg/mL. However, false positives were observed when testing seized heroin samples, caused by caffeine concentrations over 300 µg/mL. False negatives were also seen for eight nitazene compounds.

Conclusion: Caution should be exercised when deploying these nitazene test strips as frontline presumptive tests in both criminal justice and public health contexts due to the observed false negative and false positive results. While the strips successfully detected a majority of nitazene compounds, their inability to identify certain analogs poses a risk of not detecting the presence of these potent opioids in the drug supply. Additionally, the occurrence of false positives, due to the presence of caffeine-a common adulterant in illicit substances-raises concerns about their suitability for use as a harm reduction method.