Beyond Fentanyl Test Strips: Investigating Other Urine Drug Test Strips for Drug Checking Applications.

Use of immunoassay test strips for the detection of fentanyl in drug samples has become commonplace in harm reduction, law enforcement, public health, customs, and forensic science settings for testing drug product. With the increase of xylazine in the drug supply in recent years, use of xylazine test strips has also increased. As use of test strips expands, a desire to implement them for other drugs may emerge. However, since these strips are designed for urine testing, it is important to understand their applicability to testing drug product. In this work, we investigate the utility of seven types of urine immunoassay test strips - amphetamine, benzodiazepine, cocaine, methamphetamine, nitazene, opiate, and xylazine - for drug checking applications. Reproducibility, sensitivity, cross-reactivity, and the effect of prolonged exposure to elevated temperatures were studied. Generally, the tests were found to be reproducible, able to detect trace (µg/mL) levels of the analyte of interest, and minimally affected by prolonged storage at elevated temperatures. Nearly all tests showed cross-reactivity with compounds other than the analyte of interest, highlighting the need to better understand these limitations prior to implementation in a drug checking scenario. The viability of expired cocaine, fentanyl, and methamphetamine test strips was also interrogated, and little to no change in sensitivity was found even though the tests were multiple years expired.

The Detection of Xylazine in Tijuana, Mexico: Triangulating Drug Checking and Clinical Urine Testing Data.

Introduction: Xylazine is a veterinary anesthetic increasingly present alongside illicit fentanyl in the US and Canada, presenting novel health risks. Although xylazine remains less common in the Western US, Mexican border cities serve as key trafficking hubs and may have higher prevalence of novel substances, but surveillance has been limited. Methods: We examined deidentified records from the Prevencasa harm reduction clinic in Tijuana, describing urine and paraphernalia testing from patients reporting using illicit opioids within 24 hr. Xylazine (two types), fentanyl, opiate, methamphetamine, amphetamine, benzodiazepine, and nitazene test strips were used to test urine and paraphernalia samples. Paraphernalia samples were also analyzed with mass spectrometry. Results: The study consisted of 23 participants that provided both urine and paraphernalia samples. Of the participants studied, 100 %, 91.3 %, and 69.6 % reported using China White/fentanyl, methamphetamine, and tar heroin, respectively. The mean age was 41.7 years, 95.7 % were male, 65.2 % were unhoused, and 30.4 % had skin wounds at the time of sample collection.Xylazine positivity in urine, for the two types used, was 82.6 % and 65.2 %. For paraphernalia testing, the xylazine positivity was 65.2 % and 47.8 %. Confirmatory testing of paraphernalia samples by mass spectrometry indicated a 52.2 % xylazine positivity. This testing also revealed positivity rates for fentanyl (73.9 %), fluorofentanyl (30.4 %), tramadol (30.4 %), and lidocaine (30.4 %).The mass spectrometry results suggest lidocaine triggered n = 3 and n = 0 false positives among the xylazine test strip types. A total of n = 0 and n = 1 false negatives were also observed. Discussion: Xylazine is present on the U.S.-Mexico border, requiring public health intervention. High lidocaine positivity complicates the clinical detection of xylazine via testing strips. Xylazine was found to be more prevalent in urine than in paraphernalia samples. Confirmatory urine studies are needed to better understand possible complications of using test strips for toxicological testing.