Prolonged detection of urine norfentanyl in individuals enrolled in a medication for opioid use disorder in pregnancy and postpartum program: a case series

BACKGROUND

Although urine drug testing can have vast legal and social ramifications, its interpretation during pregnancy and after birth remains not well understood. Fentanyl metabolism is altered by an individual's genetics, history of opioid use, and liver function. However, little is known about the clearance of fentanyl or its primary metabolite, norfentanyl, in the peripartum period.

OBJECTIVE

We sought to identify and describe cases of delayed urine norfentanyl clearance in the pregnancy and postpartum period within our institution.

STUDY DESIGN

This study described 3 cases of delayed urine norfentanyl clearance in pregnant and postpartum individuals in a colocated obstetrics, postpartum, and addiction medicine program. This program included prescriptions for medication for opioid use disorder and weekly urine drug testing with fentanyl immunoassay with reflex confirmation testing with liquid chromatography-tandem mass spectrometry for positive results with a limit of detection of 2.5 ng/mL.

RESULTS

Low levels of norfentanyl (<16.3 ng/mL) were detected in urine 294 days, 126 days, and 231 days after the last fentanyl use. Patient self-reported abstinence was supported by consistently negative urine fentanyl levels throughout the collection period, compliant weekly urine drug tests that were otherwise only positive for buprenorphine, and negative fentanyl and norfentanyl in umbilical cord toxicology.

CONCLUSION

Despite compliance in a medication for opioid use disorder program, the presence of norfentanyl in urine has significant consequences on the maternal-child dyad in the postpartum period. Caution should be used when using low levels of norfentanyl to determine an individual's abstinence, as it can lead to further discrimination against women in medication for opioid use disorder programs.