Rates of Fentanyl Positivity in Neonatal Urine Following Maternal Analgesia During Labor and Delivery

Performance of a Norfentanyl Immunoassay in Specimens with Low Concentrations of Fentanyl and/or Norfentanyl

BACKGROUND

Many fentanyl immunoassays are limited in their ability to detect norfentanyl. Urine specimens collected from individuals who have been exposed to fentanyl frequently have detectable concentrations of norfentanyl (≥2 ng/mL) but low concentrations of fentanyl (<2 ng/mL) by LC-MS/MS. The Lin-Zhi Fentanyl II Immunoassay (Lin-Zhi) claims 100% cross-reactivity with norfentanyl and therefore may detect exposure missed by other assays.

METHODS

In addition to verifying the manufacturer's analytical sensitivity claims, we selected 92 urine specimens with low-positive Lin-Zhi results (1-99 absorbance units, lowest 10%) for analysis by the Immunalysis Health Equity Impact Assessment and ARK II fentanyl methods. The accuracy of the 3 immunoassays was compared to LC-MS/MS as the reference method.

RESULTS

Spiking studies using purified fentanyl and norfentanyl and a set of 100 consecutive specimens confirmed the manufacturer's claims of limit of detection for fentanyl (3.8 ng/mL) and norfentanyl (5.0 ng/mL). However, the 92 low-positive patient specimens demonstrated concentrations of norfentanyl and fentanyl below 2.0 ng/mL by LC-MS/MS, with 47 (51%) having only norfentanyl detected. When comparing Lin-Zhi to the Immunalysis and ARK II immunoassays, only 27 (29%) of the 92 specimens were concordant. Fifty-two (57%) of the specimens were positive by LC-MS/MS and Lin-Zhi but false negative by one or both other immunoassays. Seven specimens (8%) were positive by Lin-Zhi but negative by the other immunoassays and had undetectable concentrations (<2 ng/mL) of fentanyl and norfentanyl by LC-MS/MS.

CONCLUSIONS

The clinical sensitivity of the Lin-Zhi exceeds the manufacturer's claims, providing results comparable to LC-MS/MS methods.

High-sensitivity neonatal urine drug testing has similar positivity rates to meconium for detecting in utero exposure to methamphetamine and cocaine

Current guidelines recommend universal screening for substance use disorders in obstetric patients, and neonatal drug testing is also frequently performed. Meconium is often the preferred specimen type to detect neonatal drug exposure due to a longer window of detection compared to urine, but most laboratories send out meconium testing to specialized reference laboratories, which can delay results for several days or more. Here, we evaluate a rapid and definitive liquid chromatography-tandem mass spectrometry method for neonatal urine drug testing and compare results obtained using this method to paired meconium drug testing in 1,424 neonates for amphetamines, cocaine, cannabinoids, opiates, oxycodone and phencyclidine. Urine testing showed equivalent sensitivity to current meconium methods for detecting in utero exposure to amphetamines and cocaine.

Evaluating the Pharmacokinetics of Fentanyl in the Brain Extracellular Fluid, Saliva, Urine, and Plasma of Newborns from Transplacental Exposure from Parturient Mothers Dosed with Epidural Fentanyl Utilizing PBPK Modeling

BACKGROUND AND OBJECTIVE

Fentanyl can mitigate the mother and newborn complications resulting from labor pain. However, fentanyl shows a narrow therapeutic index between its respiratory depressive and analgesic effects. Thus, prenatally acquired high fentanyl levels in the newborn brain extracellular fluid (bECF) may induce respiratory depression which requires therapeutic drug monitoring (TDM). TDM using saliva and urine in newborns can reduce the possibility of infections and distress associated with TDM using blood. The objective of this study was to develop  a physiologically based pharmacokinetic (PBPK) model to predict fentanyl concentrations in different newborn tissues due to intrauterine exposure.

METHODS

A fentanyl PBPK model in adults after intravenous and epidural administration was built, validated, and scaled to pregnancy and newborn populations. The dose that the newborn received transplacentally at birth was calculated using the pregnancy model. Then, the newborn bECF, saliva, plasma, and urine concentrations after such a dose were predicted using the newborn PBPK model.

RESULTS

After a maternal epidural dose of fentanyl 245 µg, the predicted newborn plasma and bECF levels were below the toxicity thresholds. Furthermore, the salivary threshold levels in newborns for fentanyl analgesic and respiratory depression effects were estimated to be 0.39 and 14.7-18.2 ng/ml, respectively.

CONCLUSION

The salivary TDM of fentanyl in newborns can be useful in newborns exposed to intrauterine exposure from parturient females dosed with epidural fentanyl. However, newborn-specific values of µ-opioid receptors IC50 for respiratory depression are needed.

Advances in fentanyl testing

Fentanyl is a synthetic opioid that was approved by the FDA in the late 1960s. In the decades since, non-prescription use of fentanyl, its analogs, and structurally unrelated novel synthetic opioids (NSO) has become a worsening public health crisis. There is a clear need for accessible testing for these substances in biological specimens and in apprehended drugs. Immunoassays for fentanyl in urine are available but their performance is restricted to facilities that hold moderate complexity laboratory licenses. Immunoassays for other matrices such as oral fluid (OF), blood, and meconium have been developed but are not widely available. Point of care tests (POCT), such as lateral flow immunoassays or fentanyl test strips (FTS), are widely available but not approved by the FDA for clinical use. All immunoassays are vulnerable to false positive and false negative results. Immunoassays may or may not be able to detect fentanyl analogs and NSOs. Mass spectrometry (MS) can accurately and reliably measure fentanyl and its major metabolite norfentanyl in urine and oral fluid. MS is available at reference laboratories and large hospitals. Liquid chromatography paired with tandem mass spectrometry (LC-MS/MS) is the most widely used method and has outstanding specificity and sensitivity for fentanyl and norfentanyl. When compared to immunoassays, MS is more expensive, requires more technical skill, and takes longer to result. Newer mass spectrometry methods can measure fentanyl analogs and NSO. Both mass spectrometry assays and immunoassays [in the form of fentanyl test strips (FTS)] have potential use in harm reduction programs.

Fentanyl in the labor epidural impacts the results of intrapartum and postpartum maternal and neonatal toxicology tests

BACKGROUND

A positive urine fentanyl toxicology test may have considerable consequences for peripartum individuals, yet the extent to which fentanyl administration in a labor epidural may lead to such a positive test is poorly characterized.

OBJECTIVE

This study aimed to quantify the extent to which neuraxial fentanyl in labor neuraxial analgesia can lead to a positive peripartum maternal or neonatal urine toxicology test.

STUDY DESIGN

We performed a prospective cohort study of pregnant participants planning a vaginal delivery with neuraxial analgesia. Participants with a history of substance use disorder, hypertension, or renal or liver disease were excluded. A urine sample was collected before initiation of neuraxial analgesia, each time the bladder was emptied during labor, and up to 4 times postpartum. Neonatal urine was collected once. Urine fentanyl testing was performed using 2 common toxicology testing methods, namely immunoassay and liquid chromatography with tandem mass spectrometric detection.

RESULTS

A total of 33 maternal-infant dyads yielded a total of 178 urine specimens. All maternal specimens were negative for fentanyl using liquid chromatography with tandem mass spectrometric analysis and immunoassay before initiation of neuraxial analgesia. Intrapartum, 26 of 30 (76.7%) participants had positive liquid chromatography with tandem mass spectrometry results for fentanyl or its metabolites, and 12 of 30 (40%) participants had positive immunoassay results. Postpartum, 19 of 21 (90.5%) participants had positive liquid chromatograph with tandem mass spectrometric results, and 13 of 21 (61.9%) had a positive immunoassay result. Of the 13 neonatal specimens collected, 10 (76.9%) were positive on liquid chromatography with tandem mass spectrometry analysis, the last of which remained positive 29 hours and 50 minutes after delivery.

CONCLUSION

Neuraxial fentanyl for labor analgesia may lead to positive maternal and neonatal toxicology tests at various times after epidural initiation and cessation and at different rates depending on the testing method used. Caution should be used in interpreting toxicology test results of individuals who received neuraxial analgesia to avoid false assumptions about nonprescribed use.

Significance of CYP3A4 ∗ 1G and OPRM1 A118G Polymorphisms in Postoperative Sufentanil Analgesia in Women of Different Ethnicities

Objective. To investigate the association between CYP3A4 $\ast$ 1G and OPRM1A118G gene polymorphisms and postoperative analgesia with sufentanil in women of Zhuang ethnicity from western Guangxi, China. Methods. Forty-eight Chinese Zhuang women who underwent elective myomectomy under general anesthesia in our hospital from January 2019 to December 2020 were selected, and another 47 Chinese Han patients in the same period were selected as the control subjects. CYP3A4 $\ast$ 1G and OPRM1 A118G gene polymorphisms as well as sedation and pain scores at different time points after surgery were compared between the two groups of patients to analyze the relationship between the degree of pain and dosage of sufentanil and to analyze the effect of gene polymorphisms on the occurrence of adverse reactions. Results. The frequencies of $\ast$ 1/ $\ast$ 1G and $\ast$ 1G/ $\ast$ 1G genotypes, allele $1\ast \text{G}$ of CYP3A4 $\ast$ 1G and genotypes AA, and allele A of OPRM1 A118G in Zhuang patients were lower than those in Han patients, while the frequencies of $\ast$ 1/ $\ast$ 1, allele $\ast$ 1 of CYP3A4 $\ast$ 1G and genotypes AG, genotypes GG, and allele G of OPRM1 A118G were higher in Zhuang women. There was no significant difference in the Ramsay and VAS scores between the two groups at different time points after surgery, but the sufentanil use in Zhuang patients was higher than in Han patients at different time points after surgery. In addition, sufentanil use was highest in Zhuang patients with the $\ast$ 1/ $\ast$ 1 genotype of the CYP3A4 $\ast$ 1G gene. No significant difference was found in the incidence of adverse reactions during analgesia between the two groups. Conclusion. CYP3A4 $\ast$ 1G could be associated with postoperative sufentanil analgesia in Zhuang patients in western Guangxi and should be considered when developing personalized analgesia regimens.

Toxicology as a diagnostic tool to identify the misuse of drugs in the perinatal period

The use, misuse, and abuse of substances are a continued public health concern in this country and around the world. Perinatal exposure to substances of abuse is associated with several long-term negative consequences for the neonate. Limited resources exist to assist perinatal health professionals on this very complex subject. The purpose of this document is to provide additional information about selecting monitoring protocols, the specifics of appropriate testing methodologies, and the interpretation of toxicological findings. Understanding these concepts better allows perinatal healthcare professionals to be a voice for the voiceless in order to protect and enrich lives during this unprecedented opioid epidemic.