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Aims: Buprenorphine is effective at reducing relapse to opioid misuse, morbidity and mortality in opioid-dependent patients. Urine drug screening (UDS) to assess adherence is used routinely in opioid agonist treatment (OAT). The primary aim of this study was to determine factors which may be associated with a negative qualitative urine drug screen for buprenorphine in OAT patients., Methods: This prospective pilot study was conducted at a tertiary addiction medicine centre. Twenty participants on stable treatment underwent supervised administration of sublingual buprenorphine. Matched urine and blood samples were collected prior to and 2, 4 and 6 hours after buprenorphine administration. Qualitative urine drug screen results were obtained using gas chromatography-mass spectrometry (GC-MS), while quantitative blood and urine results were obtained using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)., Results: Qualitative urine assay yielded a negative result for buprenorphine in 57% of tested samples. The median concentration of urinary buprenorphine was 167 mcg/L (range: 2-1730 mcg/L). Thirty percent of all blood samples did not detect buprenorphine (range 0-18 mcg/L). Positive qualitative urine drug screen results were associated with higher urine (343 mcg/L compared with 75 mcg/L; P < .05) and blood (4 mcg/L compared with 2 mcg/L; P < .05) buprenorphine concentrations. Median urine concentrations of buprenorphine were highest at 2 hours and were higher in participants receiving CYP3A4 inhibitors., Conclusion: Interpretation of qualitative urine drug screens to assess adherence in OAT is complex. Poor adherence with treatment cannot be assumed in patients returning a negative qualitative GC-MS urine drug screen., (© 2022 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Introduction: Urine drug screens (UDS) assist in clinical planning and assessment of adherence in opioid agonist treatment (OAT). Urine drug screens may also be used in criminal justice and child protection settings. Buprenorphine (BPN) UDS testing is complex. Immunoassay often does not detect BPN and gas chromatography-mass spectrometry (GC-MS) is needed. A limited understanding of testing can negatively influence UDS interpretation and clinical decision making., Objectives: The primary aim was to determine detection rates of BPN in UDS in participants on BPN or buprenorphine/naloxone (BNX) treatment. The secondary aim was to identify if comorbidities, sex, co-prescribed medications, or dosing site and observation were associated with BPN detection., Setting: Public outpatient clinic in a specialist addiction treatment service., Design/participants: In this retrospective observational study, records of clients on supervised BPN/BNX treatment between September 2017 and 2018 were reviewed., Measures: Data extracted included UDS results, age, sex, indication for BPN, frequency of observed doses, dose of BPN, dosing site, comorbid medical conditions, and medications., Results: One hundred and sixty-one medical records were reviewed. Ninety-seven (60 percent) underwent screening urine immunoassay. Of these 97, 51 (53 percent) had further GC-MS testing for BPN of which 22 (43 percent) did not detect BPN despite directly observed OAT. Co-prescription of medications known to interact with cytochrome P450 3A4 was associated with nondetection of BPN (p < 0.05). No significant association between median dose, dosing site, and observed dosing and BPN detection was identified., Conclusion: Urine drug testing for BPN is complex. Failure to detect BPN does not betoken nonadherence to treatment and is associated with co-prescription of drugs interacting with cytochrome P450 3A4.