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Updated: Dec 6, 2025

Author Spotlight: An Efficient Methodology to Confidently Differentiate and Characterize Fentanyl Analogs
Published on: November 8, 2024
Delayed Norfentanyl Clearance During Pregnancy
Amita Wanar1, Kelley Saia, Thomas A Field
1Departments of Obstetrics and Gynecology and Psychiatry, Boston University School of Medicine, and the Department of Obstetrics and Gynecology, Boston Medical Center, Boston, Massachusetts.
Background:
We report a case of delayed norfentanyl clearance in a 33-year-old pregnant woman. Norfentanyl is the major metabolite of fentanyl.
Case:
A multigravid woman with opioid use disorder presented at 7 weeks of gestation for treatment. Despite opioid abstinence, her urine was positive for norfentanyl on 10 distinct gas chromatography-mass spectrometry urine screens. The results demonstrated a steady decrease of norfentanyl over the course of 70 days after her last fentanyl usage, far exceeding expected rates of fentanyl clearance.
Conclusion:
This case highlights the importance of acknowledging pregnancy, genetic, or medication-induced changes to fentanyl pharmacokinetics when interpreting urine tests, especially given the potential sequelae of a false-positive urine test result.
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