Norbuprenorphine Research Articles

Interaction between buprenorphine and norbuprenorphine in neonatal opioid withdrawal syndrome

Buprenorphine (BUP) is the preferred treatment for opioid use disorder during pregnancy but can cause neonatal opioid withdrawal syndrome (NOWS). Norbuprenorphine (NorBUP), an active metabolite of BUP, is implicated in BUP-associated NOWS. We hypothesized that BUP, a low-efficacy agonist of mu opioid receptors, will not antagonize NorBUP, a high-efficacy agonist of mu opioid receptors, in producing NOWS. To test this hypothesis, we treated pregnant Long-Evans rats with BUP (0, 0.01, 0.1 or 1mg/kg/day) ± NorBUP (1mg/kg/day) from gestation day 9 until pup delivery, and tested pups for opioid dependence using our established NOWS model. We used LC-MS-MS to quantify brain concentrations of BUP, NorBUP, and their glucuronide conjugates. BUP had little effect on NorBUP-induced NOWS, with the exception of 1mg/kg/day BUP significantly increasing NorBUP-induced NOWS by 58% in females. BUP and NorBUP brain concentrations predicted NOWS in multiple linear regression models. Interestingly, NorBUP contributed more to NOWS in females (βNorBUP = 51.34, p = 0.0001) than in males (βNorBUP = 19.21, P = 0.093), while BUP was similar for females (βBUP = 10.62, P = 0.0017) and males (βBUP = 11.38, P = 0.009). We are the first to report that NorBUP induces NOWS in the presence of BUP and it is more influential in females than males in the contribution of NorBUP to BUP-associated NOWS. These findings suggest that females are more susceptible to NorBUP-induced NOWS, and that treatment strategies that reduce prenatal NorBUP exposure may be more effective for females than males.

Deuterated buprenorphine retains pharmacodynamic properties of buprenorphine and resists metabolism to the active metabolite norbuprenorphine in rats.

Introduction: An active metabolite of buprenorphine (BUP), called norbuprenorphine (NorBUP), is implicated in neonatal opioid withdrawal syndrome when BUP is taken during pregnancy. Therefore, reducing or eliminating metabolism of BUP to NorBUP is a novel strategy that will likely lower total fetal exposure to opioids and thus improve offspring outcomes. Precision deuteration alters pharmacokinetics of drugs without altering pharmacodynamics. Here, we report the synthesis and testing of deuterated buprenorphine (BUP-D2). Methods: We determined opioid receptor affinities of BUP-D2 relative to BUP with radioligand competition receptor binding assays, and the potency and efficacy of BUP-D2 relative to BUP to activate G-proteins via opioid receptors with [35S]GTPγS binding assays in homogenates containing the human mu, delta, or kappa opioid receptors. The antinociceptive effects of BUP-D2 and BUP were compared using the warm-water tail withdrawal assay in rats. Blood concentration versus time profiles of BUP, BUP-D2, and NorBUP were measured in rats following intravenous BUP-D2 or BUP injection. Results: The synthesis provided a 48% yield and the product was ≥99% deuterated. Like BUP, BUP-D2 had sub-nanomolar affinity for opioid receptors. BUP-D2 also activated opioid receptors and induced antinociception with equal potency and efficacy as BUP. The maximum concentration and the area under the curve of NorBUP in the blood of rats that received BUP-D2 were over 19- and 10-fold lower, respectively, than in rats that received BUP. Discussion: These results indicate that BUP-D2 retains key pharmacodynamic properties of BUP and resists metabolism to NorBUP and therefore holds promise as an alternative to BUP.

481 Interactions between buprenorphine and norbuprenorphine in neonatal opioid withdrawal syndrome

OBJECTIVES/GOALS: Buprenorphine (BUP) is used for opioid use disorder during pregnancy but causes neonatal opioid withdrawal syndrome (NOWS). The goal of this study was to determine the contribution of the active metabolite, norbuprenorphine (NorBUP), to the development of NOWS when the parent drug, BUP, is administered during pregnancy. METHODS/STUDY POPULATION: Subcutaneously implanted osmotic minipumps delivered BUP (0, 0.01, 0.1 or 1 mg/kg/day) ± NorBUP (1 mg/kg/day) to pregnant Long-Evans rats from gestation day 9 until after delivery. NOWS was measured between 3 and 12 hours after delivery. Withdrawal was precipitated by an intraperitoneal injection of a mu opioid receptor antagonist naltrexone (NTX; 0, 1 or 10 mg/kg), and movement duration (MD; a validated proxy for NOWS) was measured using Noldus Ethovision. Concentrations of BUP, NorBUP, and their glucuronide conjugates in the brains of neonatal littermates not undergoing withdrawal testing were determined using LC/MS/MS. Two-way ANOVA and multiple linear regression analyses tested for interactions between BUP and NorBUP on MD and related brain concentrations to MD, respectively. RESULTS/ANTICIPATED RESULTS: There was no interaction effect between BUP and NorBUP on MD for either sex or at any dose of naltrexone. In females, but not males, BUP (1 mg/kg/day) significantly increased NorBUP-induced MD by 58% following an injection with 1 mg/kg NTX. A multiple linear regression model that included BUP and NorBUP brain concentrations as predictors of MD was significant and well-fitting [FEMALES: F (2, 40) = 23.97, P < .0001, adj R2 = 0.52; MALES: F (2, 40) = 5.84, P = .0059, adj R2 = 0.19]. There was a differential contribution of NorBUP brain concentrations to MD based on sex. The partial regression coefficient for NorBUP was 51.34 (p < .0001) for females and 19.21 (p = 0.093) for males. The partial regression coefficient for BUP was similar for females and males (FEMALES:βBUP = 10.62, p = .0017; MALES:βBUP = 11.38, p = .009). DISCUSSION/SIGNIFICANCE: We show for the first time a differential contribution of NorBUP to BUP-associated NOWS in each sex, suggesting sex differences in NorBUP susceptibility and implicating that treatment strategies reducing prenatal NorBUP exposure may be more effective for females than males.

Maternal-fetal biodisposition of buprenorphine and its metabolites in opioid dependent pregnant individuals

To determine the concentration of buprenorphine (BUP) and its metabolites in maternal and fetal samples and investigate the relationship between BUP concentrations and neonatal opioid withdrawal syndrome (NOWS). Matched maternal and fetal samples were collected from 12 individuals maintained on BUP for opioid use disorder during pregnancy. All delivered at term (≥37 weeks gestation) via cesarean section. Samples were collected at delivery and included maternal plasma (PL), amniotic fluid (AF), and umbilical cord blood (CB). Concentrations of BUP, its biologically active metabolite norbuprenorphine (NBUP) and its inactive metabolites glucuronide forms of buprenorphine (BUP-Gluc) and norbuprenorphine (NBUP-Gluc) were determined by liquid chromatography-mass spectrometry. The concentrations of BUP and its metabolites were compared between neonates who developed NOWS, defined as withdrawal symptoms requiring pharmacologic treatment, and those who did not. Five (42%) of neonates born to mothers in the study developed NOWS. There was no difference in gestational age, birthweight or other baseline characteristics between the two groups. All individuals in the study were receiving 16 mg daily of BUP at delivery. BUP concentrations were higher in cord blood (0.65 v 0.31ng/mL, p=0.01) and amniotic fluid (0.64 v 0.0 ng/mL, p=0.04) in neonates who developed NOWS, compared to those who did not. The concentrations of NBUP were also higher in neonates who developed NOWS (2.01 v 0.0ng/mL, p=0.03). There were no differences in maternal plasma concentrations between the two groups. Despite similar maternal dosing and plasma concentrations, NBUP concentrations in AF and BUP concentrations in AF and CB were higher for infants later diagnosed with NOWS, suggesting accumulation of the drug in the fetal compartment. Further studies are needed to determine the mechanisms and whether analysis of these specimens at delivery may help predict NOWS in buprenorphine-exposed neonates.

Do buprenorphine doses and ratios matter in medication assisted treatment adherence.

IntroductionBuprenorphine (BUP), generally prescribed as buprenorphine/naloxone, is a key component of medication-assisted treatment (MAT) to manage opioid use disorder. Studies suggest higher doses of BUP increase treatment adherence. Routine urine drug screens (UDS) assist in monitoring MAT adherence via measurement of excreted BUP and its metabolite, norbuprenorphine (NBP). The clinical significance between BUP/NBP concentrations and their ratios for assessing adherence and substance use is not well-described.MethodsWe conducted a single-center, retrospective chart review of 195 clients age ≥18 years enrolled in a local MAT program from August 2017 to February 2021. Demographics, BUP doses, prescription history, and UDS results were collected. Participants were divided based on MAT adherence (<80% vs ≥80%) and median total daily dose (TDD) of BUP (≥16 mg vs <16 mg) in addition to pre- and post-COVID-19 cohorts.ResultsMedian BUP/NBP urinary concentrations were significantly correlated with MAT adherence (P < .0001 for each) and a reduced percentage of positive UDS for opioids (P = .0004 and P < .0001, respectively) but not their ratios. Median TDD of BUP ≥16 mg (n = 126) vs <16 mg (n = 68) was not correlated with MAT adherence (P = .107) or incidence of nonprescription use (P = .117). A significantly higher incidence of UDS positive for opiates (P = .049) and alcohol (P = .035) was observed post-COVID-19.DiscussionClients appearing adherent to MAT who had higher concentrations of urinary BUP/NBP demonstrated a reduced incidence of opioid-positive UDS independent of the BUP dose prescribed. An increase in opioid- and alcohol-positive UDSs were observed during the COVID-19 pandemic.

Investigation of buprenorphine-related deaths using urinary metabolite concentrations.

Quantitative analysis of postmortem urine, instead of blood, for buprenorphine and metabolites may provide additional evidence for the diagnosis of fatal buprenorphine poisoning. In this study, 247 autopsy urine samples, previously testing positive for buprenorphine or norbuprenorphine, were quantitatively reanalysed with a recently developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for unconjugated buprenorphine (BUP), norbuprenorphine (NBUP), naloxone (NAL), and their respective conjugated metabolites, buprenorphine glucuronide (BUPG), norbuprenorphine glucuronide (NBUPG), and naloxone glucuronide (NALG). The cases were divided, according to medical examiners' decision, to buprenorphine poisonings and other causes of death. The groups were compared for urinary concentrations and metabolite concentration ratios of the six analytes. All median concentrations were higher in the buprenorphine poisoning group. The median concentration of BUPG was significantly higher and the median metabolite ratios NBUP/BUP, NBUPG/BUPG, and NBUPtotal/BUPtotal were significantly lower in poisonings than in other causes of death. Naloxone-related concentrations and ratios were not significantly different between the groups.

Determination of buprenorphine, norbuprenorphine, naloxone, and their glucuronides in urine by liquid chromatography-tandem mass spectrometry.

A liquid chromatography-tandem mass spectrometry method for the simultaneous quantification of buprenorphine (BUP), norbuprenorphine (NBUP), naloxone (NAL), and their glucuronide conjugates BUP-G, NBUP-G, and NAL-G in urine samples was developed. The method, omitting a hydrolysis step, involved non-polar solid-phase extraction, liquid chromatography on a C18 column, electrospray positive ionization, and mass analysis by multiple reaction monitoring. Quantification was based on the corresponding deuterium-labelled internal standards for each of the six analytes. The limit of quantification was 0.5μg/L for BUP and NAL, 1μg/L for NAL-G, and 3μg/L for NBUP, BUP-G, and NBUP-G. Using the developed method, 72 urine samples from buprenorphine-dependent patients were analysed to cover the concentration ranges encountered in a clinical setting. The median (maximum) concentration was 4.2μg/L (102 μg/L) for BUP, 74.7μg/L (580 μg/L) for NBUP, 0.9μg/L (85.5μg/L) for NAL, 159.5μg/L (1370 μg/L) for BUP-G, 307.5μg/L (1970 μg/L) for NBUP-G, and 79.6μg/L (2310 μg/L) for NAL-G.

Buprenorphine Metabolism in Human Liver, Human Placenta, and Recombinant Cyp19 Microsomes

Background and Hypothesis: Buprenorphine (BUP), a partial opioid agonist, is commonly used to treat opioid use disorder in pregnant women. BUP is metabolized in the liver by cytochrome P450s (CYP) and UDPGlucuronosyltransferases (UGT). Compared to non-pregnant women, higher doses of BUP are needed during pregnancy to maintain therapeutic concentrations. We hypothesize that the placenta has a role in the metabolism of BUP, thus contributing to the need for higher doses during pregnancy.&#x0D; Experimental Design or Project Methods: : BUP was incubated with human liver microsome (HLM), human placenta microsome (HPM) or recombinant CYP19 microsome (rCYP19). Norbuprenorphine (Nor-BUP) formation was measured by HPLC/MS/MS (Thermo TSQ Quantum Ultra). Positive controls included midazolam for HLMs and testosterone for HPMs and rCYP19, and negative controls were without NADPH. Initial experiments assessed linearity with time and protein concentration. Subsequently, BUP concentrations were varied and Nor-BUP formation vs. BUP concentration was fitted to the Michaelis–Menten equation (GraphPad Prism) to calculate Km and Vmax.&#x0D; Results: The Km was 11.89 μM and Vmax was 0.4627 μmol/min/mg for Nor-BUP formation following incubation of BUP (0-20 µM) with HLM. Higher concentrations of BUP indicated non-typical Michaelis–Menten kinetics. Results from the HPM show metabolism of BUP to Nor-BUP is present in the placenta. Incubation of BUP in rCYP19, an enzyme known to be in human placenta, resulted in Nor-BUP formation, indicating its role in BUP metabolism.&#x0D; Conclusions and Potential Impact: : The Km and Vmax values generated from concentrations of 5-20 μM in HLM is comparable with existing data. Because multiple enzymes breakdown BUP with different Km and Vmax values, a curve not adhering to the normal Michaelis–Menten shape over 20 μM BUP is reasonable in HLMs. Formation of Nor-BUP following incubation of BUP in rCYP19 and HPMs suggest their role in the metabolism of BUP in pregnant women. Understanding the role of placenta in metabolizing BUP will provide insight to fetal drug exposure. Placental metabolism of BUP would possibly indicate lower exposure to BUP but higher exposure to nor-BUP to the fetus. Future directions of this study will quantify placental metabolism of BUP, investigate other pathways of BUP metabolism in the placenta, and determine drug interactions that may exacerbate Neonatal Abstinence Syndrome when coadministered with BUP.

Bupenorphine in Wisconsin Drivers: Concerns for Impairment?

Opinions vary on whether buprenorphine can cause impairment in drivers. Relatively little information on the observed effects of buprenorphine, outside a laboratory or a controlled driving course, exist in the literature. The Wisconsin State Laboratory of Hygiene monitored the detection of buprenorphine and its pharmacologically active metabolite, norbuprenorphine (NBUP), in Wisconsin drivers over a 2-year period. A total of 204 individuals (78 females and 126 males) were driving under the influence of buprenorphine and/or NBUP. Concentrations in whole blood (ng/mL) ranged (mean) from 0.6 to 14 (2.0) and 0.5 to 20 (2.1) for buprenorphine and NBUP, respectively. Poly-substance use is extremely prevalent in Wisconsin operating while intoxicated casework, so prevalent that only four of the previously described cases had buprenorphine and/or NBUP as the only drug(s) detected. This paper summarizes and highlights the case histories and observed impairments of those four cases. Law enforcement (LE) made contact with three of the four subjects due to either a crash or poor/reckless driving. Police reports and observations made by LE, including drug recognition expert (DRE) evaluations, were collected. Physical and behavioral observations made by LE varied and included a combination of narcotic analgesic, central nervous system depressant- and stimulant-like effects. Impaired balance and lack of coordination during the administration of the Standardized Field Sobriety Tests were documented by the arresting officers and/or the DRE. While the number of buprenorphine-only cases reported here is limited, the results demonstrate the complex paradigm associated with forensic interpretation of buprenorphine in driving under the influence of drugs casework and the frequency of poly-substance administration in Wisconsin drivers.

Urine is superior to oral fluid for detecting buprenorphine compliance in patients undergoing treatment for opioid addiction

BackgroundBuprenorphine (BUP) is commonly used in opioid agonist medication-assisted treatment (OA-MAT). Oral fluid (OF) is an attractive option for compliance monitoring during OA-MAT as collections are observed and evidence suggests that OF is less likely to be adulterated than urine (UR). However, the clinical and analytical performance of each matrix for monitoring BUP compliance has not been well studied. MethodsWe collected 260 paired OF and UR specimens. Concentrations of buprenorphine (BUP) and norbuprenorphine (NBUP) were measured by liquid chromatography-tandem mass spectrometry (LC–MS/MS) in each matrix. The glucuronide metabolites and naloxone concentrations were also measured in UR by LC–MS/MS. Medications were reviewed and UR creatinine concentrations were determined. Results147/260 specimens (57%) were positive for BUP and/or metabolites in one or both matrices. BUP and/or metabolites were more likely to be detected in UR (p < 0.001). 1 OF specimen and 12 UR specimens were considered adulterated/substituted. The majority of patients prescribed BUP were positive for BUP in UR (97%) as opposed to OF (78%). The detection of undisclosed use approximately doubled in UR. ConclusionsUR is the preferred matrix for detecting both buprenorphine compliance and undisclosed use. Clinicians should consider the ease of collection, risk of adulteration and detection of illicit drug use when deciding on an appropriate matrix. If OF testing is clinically necessary, UR should be measured in conjunction with OF at least periodically to avoid false negative BUP results.

Ascorbic Acid Improves the Stability of Buprenorphine in Frozen Whole Blood Samples.

Buprenorphine (BUP) was not long-term stable in whole blood samples preserved with fluoride citrate (FC) and fluoride oxalate (FX) mixtures when stored at -20°C. On average, only half of the initial concentrations of BUP was recovered after 12 weeks of storage at -20°C when interrupted by 3-4 thaw/freeze cycles. Norbuprenorphine (NBUP) was less unstable; approximately 90% was recovered after 12 weeks of storage at -20°C. The instability was less at 5°C, but the formation of BUP and NBUP from their glucuronides was observed at that temperature, especially in FC-preserved blood. The substances were stable for at least 5 months when stored uninterrupted at -80°C. The instability of BUP and NBUP in FC- and FX-preserved whole blood stored at -20°C was eliminated when the samples were modified with 30 mM ascorbic acid (ASC) prior to storage. The mean recoveries were greater than 95% after a 5-month interrupted storage period at -20°C when modified with ASC.

In Utero Exposure to Norbuprenorphine, a Major Metabolite of Buprenorphine, Induces Fetal Opioid Dependence and Leads to Neonatal Opioid Withdrawal Syndrome.

Buprenorphine is the preferred treatment of opioid use disorder during pregnancy but can cause fetal opioid dependence and neonatal opioid withdrawal syndrome (NOWS). Notably, withdrawal severity is independent of maternal buprenorphine dose, suggesting that interindividual variance in pharmacokinetics may influence risk and severity of NOWS. Using a rat model of NOWS, we tested the hypothesis that clinically relevant doses of the active metabolite norbuprenorphine (NorBUP) can induce in utero opioid dependence, manifested as naltrexone-precipitated withdrawal signs in the neonate. Pregnant Long-Evans rats were implanted with 14-day osmotic minipumps containing vehicle, morphine (positive control), or NorBUP (0.3-10 mg/kg per day) on gestation day 9. By 12 hours post-delivery, an intraperitoneal injection of the opioid antagonist naltrexone (1 or 10 mg/kg) or saline was administered to pups. Precipitated withdrawal signs were graded by raters blinded to treatment conditions. In a separate group, NorBUP concentrations in maternal and fetal blood and brain on gestation day 20 were determined by liquid chromatography-tandem mass spectrometry. Steady-state maternal blood concentrations of NorBUP in dams infused with 1 or 3 mg/kg per day were comparable to values reported in pregnant humans treated with buprenorphine (1.0 and 9.6 ng/ml, respectively), suggesting a clinically relevant dosing regimen. At these doses, NorBUP increased withdrawal severity in the neonate as shown by an evaluation of 10 withdrawal indicators. These findings support the possibility that NorBUP contributes to fetal opioid dependence and NOWS following maternal buprenorphine treatment during pregnancy.

The Effects of P‐glycoprotein Inhibition on Norbuprenorphine‐induced Neonatal Abstinence Syndrome (NAS)

Treating pregnant, opioid‐addicted women with the opioid buprenorphine improves mother‐child outcomes, but can cause neonatal abstinence syndrome (NAS), a potentially life‐threatening withdrawal syndrome newborns often develop following chronic prenatal exposure to opioids. NAS severity is independent of maternal buprenorphine dose, suggesting that inter‐individual variance in the pharmacokinetics of buprenorphine may influence NAS. We previously showed that prenatal exposure to the major active metabolite of buprenorphine, norbuprenorphine (NorBUP), can induce NAS. NorBUP is a substrate of the highly polymorphic placental efflux transporter P‐glycoprotein, which transports its substrates from fetal to maternal circulation. We tested the hypothesis that inhibiting P‐glycoprotein increases NorBUP‐induced NAS severity. We administered a subthreshold dose of NorBUP or vehicle to pregnant rats from gestation day (GD) 9 until post‐delivery and treated them twice daily with the p‐glycoprotein inhibitor Elacridar or vehicle on GD18‐21. After delivery, pups were observed for precipitated withdrawal signs following administration of naltrexone or saline. NorBUP and Elacridar together, but not individually, increased naltrexone‐precipitated withdrawal signs, providing the first evidence that P‐glycoprotein activity can substantially modulate the effects of NorBUP on the fetus and may therefore contribute to the uncoupling of maternal buprenorphine dose and NAS severity.Support or Funding InformationThe project described was supported by a Summer Undergraduate Research Fellowship from the American Society for Pharmacology and Experimental Therapeutics, the UAMS Fellow‐to‐Faculty Award (Arkansas Biomedical Institute, Tobacco Settlement Funds), a UAMS Research Scholar Pilot Grant Award in Child Health, and the Translational Research Institute (TRI), grants 1U54TR001629‐01A1 and KL2TR000063 through the National Center for Advancing Translational Sciences of the National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Addressing discordant quantitative urine buprenorphine and norbuprenorphine levels: Case examples in opioid use disorder

IntroductionUrine adulteration is a concern among patients treated for opioid use disorder. Quantitative urine testing for buprenorphine (B) and norbuprenorphine (NB), and the appropriate interpretation of B and NB levels, can facilitate constructive conversations with patients that may lead to modifications in the treatment plan, and strengthening of the patient-provider relationship. Case summaryThree cases are presented in which discordant urine B and NB levels were recognized. Each patient was submerging buprenorphine/naloxone strips in their urine to mask ongoing illicit drug use. The authors used an approach to addressing intentional adulteration of urine samples that adheres to the principles of harm-reduction, the centrality of the patient-provider relationship, and the acknowledgment that ongoing illicit drug use and subsequent dishonesty about disclosure may be common among persons with substance use disorders. Each of the three patients ultimately endorsed diluting their urine, which allowed for strengthening of the patient-provider relationship and modifications to their treatment plans. Two of the three patients stabilized and achieved abstinence, while the third was eventually referred to a methadone treatment program. ConclusionProviders should routinely monitor B and NB levels, rather than qualitative screening alone, and discordant levels should elicit a timely conversation with the patient. The authors use of a nonjudgmental approach to address urine adulteration, including giving patients an opportunity to reflect on potential solutions, has been effective at helping patients and providers to reestablish a therapeutic alliance and maintain retention in treatment.

Highly sensitive simultaneous quantification of buprenorphine and norbuprenorphine in human plasma by magnetic solid-phase extraction based on PpPDA/Fe3O4 nanocomposite and high-performance liquid chromatography

A rapid and sensitive method based on magnetic solid-phase extraction coupled to high-performance liquid chromatography with ultraviolet detection was developed for the simultaneous determination of buprenorphine (BPN) and its major metabolite, norbuprenorphine (N-BPN), in human plasma samples. Poly (para-phenylenediamine)-modified Fe3O4 nanoparticles (PpPDA/Fe3O4) were synthesized and used as a magnetic adsorbent for the extraction and preconcentration of BPN and N-BPN in biological samples. The synthesized nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and vibrating sample magnetometery. An isocratic separation was achieved on a Nova-Pak C18 reversed-phase column using a mobile phase consisting phosphate buffer (pH 3.4) and acetonitrile (50:50, v/v) at a flow rate of 1.0 mL min−1. The detection was conducted at 280 nm. Under the optimum conditions, the calibration curves for BPN and N-BPN were linear in the ranges 3.0–150.0 and 1.0–120.0 ng mL−1, respectively. The sensitivity was also high with limit of detection of 0.8 and 0.3 ng mL−1 for BPN and N-BPN in plasma, respectively. The method was successfully applied to the extraction and determination of BPN and N-BPN in human plasma samples with an average recovery of 98.10 and 96.41%, respectively.

Pregnancy Increases Norbuprenorphine Clearance in Mice by Induction of Hepatic Glucuronidation.

Norbuprenorphine (NBUP) is the major active metabolite of buprenorphine (BUP) that is commonly used to treat opiate addiction during pregnancy; it possesses 25% of BUP's analgesic activity and 10 times BUP's respiratory depression effect. To optimize BUP's dosing regimen during pregnancy with better efficacy and safety, it is important to understand how pregnancy affects NBUP disposition. In this study, we examined the pharmacokinetics of NBUP in pregnant and nonpregnant mice by administering the same amount of NBUP through retro-orbital injection. We demonstrated that the systemic clearance (CL) of NBUP in pregnant mice increased ∼2.5-fold compared with nonpregnant mice. Intrinsic CL of NBUP by glucuronidation in mouse liver microsomes from pregnant mice was ∼2 times greater than that from nonpregnant mice. Targeted liquid chromatography tandem-mass spectrometry proteomics quantification revealed that hepatic Ugt1a1 and Ugt2b1 protein levels in the same amount of total liver membrane proteins were significantly increased by ∼50% in pregnant mice versus nonpregnant mice. After scaling to the whole liver with consideration of the increase in liver protein content and liver weight, we found that the amounts of Ugt1a1, Ugt1a10, Ugt2b1, and Ugt2b35 protein in the whole liver of pregnant mice were significantly increased ∼2-fold compared with nonpregnant mice. These data suggest that the increased systemic CL of NBUP in pregnant mice is likely caused by an induction of hepatic Ugt expression and activity. The data provide a basis for further mechanistic analysis of pregnancy-induced changes in the disposition of NBUP and drugs that are predominately and extensively metabolized by Ugts.

The Role of Norbuprenorphine in Buprenorphine‐Induced Neonatal Abstinence Syndrome: A Pilot Study

Opioid abuse during pregnancy may cause drug dependence in the fetus, and the abrupt discontinuation of opioid exposure at birth may induce neonatal abstinence syndrome (NAS) during the first week of life. NAS is characterized by inconsolable high‐pitched crying, tremor, vomiting, diarrhea, hypersensitivity, and sleep disturbances. Buprenorphine (BUP), a mu‐opioid receptor partial agonist, is administered as a substitution therapy to treat opioid use disorder during pregnancy. BUP improves neonatal outcome compared with methadone or no treatment, but BUP exposure often leads to NAS. Furthermore, NAS severity is independent of maternal BUP dose throughout pregnancy, suggesting that individual differences in maternal‐fetal BUP pharmacology may increase NAS susceptibility in some newborns. One possible explanation is that fetal exposure to norbuprenorphine (NorBUP), a metabolite of BUP that has high affinity and efficacy at the mu‐opioid receptor, differs across the BUP‐treated population and drives individual differences in the development of opioid dependence. This study tested the hypothesis that NorBUP can induce NAS. To test this hypothesis, we developed a novel model of NAS in which exposure to opioids occurs continuously across fetal development. Pregnant rats were implanted with subcutaneous minipumps containing NorBUP (0.1 or 0.3 mg/kg*day) or vehicle (5 % Emulphor) on gestation day (GD) 9. Treatment continued until delivery. Upon delivery, half of the pups were observed and scored for signs of precipitated withdrawal for 10 minutes after administration of the mu‐opioid receptor antagonist naltrexone (1 or 10 mg/kg, i.p.) or saline (10 ml/kg). Because of the CNS immaturity of the neonatal rat pup relative to the human newborn, this group models opioid dependence in preterm newborns. To model NAS at term, the other half of each litter was fostered to an untreated dam and received subcutaneous injections of NorBUP (0.05 mg/kg or 1.5 mg/kg) every 12 hours (BID) until they were tested for precipitated opioid withdrawal on postnatal day (PD) 7. Few withdrawal signs were observed in the pups tested within 24 hours of delivery, but PD7 pups exposed to the high dose of NorBUP in utero and after birth exhibited significantly more “wall climbing” and less “quiet” signs when challenged with naltrexone, indicating opioid withdrawal. The results of these preliminary studies suggest that NorBUP can induce opioid dependence in the neonatal pup. Ongoing experiments will determine fetal brain concentrations of NorBUP after maternal exposure to NorBUP (GD 9‐ GD20). Results of this experiment will be used to determine additional doses of NorBUP to be tested in the novel rat model of NAS.Support or Funding InformationSupport for this study was provided by the UAMS Fellow to Faculty award and the UAMS Tobacco Research Committee Tobacco Settlement Funds

Buprenorphine, Norbuprenorphine, R-Methadone, and S-Methadone Upregulate BCRP/ABCG2 Expression by Activating Aryl Hydrocarbon Receptor in Human Placental Trophoblasts.

Opioid dependence during pregnancy is a rising concern. Maintaining addicted pregnant women on long-acting opioid receptor agonist is the most common strategy to manage drug abuse in pregnant women. Methadone (MET) and buprenorphine (BUP) are widely prescribed for opiate maintenance therapy. Norbuprenorphine (NBUP) is the primary active metabolite of BUP. These medications can cross the placenta to the fetus, leading to postpartum neonatal abstinence syndrome. Despite their use during pregnancy, little is known about the cellular changes in the placenta brought about by these drugs. In this study, we showed that BUP, NBUP, and MET at clinically relevant plasma concentrations significantly induced BCRP mRNA up to 10-fold in human model placental JEG3 and BeWo cells and in primary human villous trophoblasts, and this induction was abrogated by CH223191, an aryl hydrocarbon receptor (AhR)-specific antagonist. These drugs increased AhR recruitment onto the AhR-response elements and significantly induced breast cancer resistance protein (BCRP) gene transcription. AhR overexpression further increased BCRP mRNA and protein expression. Knockdown of AhR by shRNA decreased BCRP expression, and this decrease was reversed by rescuing AhR expression. Finally, induction of BCRP expression in JEG3 and BeWo cells was accompanied by an increase in its efflux activity. Collectively, we have demonstrated, for the first time, that BUP, NBUP, and MET are potent AhR agonists and can induce BCRP in human placental trophoblasts by activating AhR. Given the critical role of BCRP in limiting fetal exposure to drugs and xenobiotics, long-term use of these medications may affect fetal drug exposure by altering BCRP expression in human placenta.

Editor's Highlight: Neurorespiratory Effects of Buprenorphine and Ethanol in Combination: A Mechanistic Study of Drug-Drug Interactions in the Rat.

Respiratory depression and fatalities have been attributed to ethanol/buprenorphine (BUP) combination in drug addicts maintained with BUP/naloxone or BUP alone. The exact mechanisms of the ethanol/BUP interaction and the contribution to the toxicity of norbuprenorphine (NBUP), the main BUP metabolite with respiratory depressant properties are unknown. We investigated the sedative and plethsymographic effects resulting from the co-administration of intragastric ethanol (3 g/kg) and intravenous BUP (30 mg/kg) in Sprague-Dawley rats. We determined the whole blood pharmacokinetics of ethanol (using gas chromatography coupled to mass spectrometry), BUP and its metabolites (using liquid chromatography coupled to tandem mass spectrometry) and investigated the mechanisms of drug-drug interactions in the presence or absence of naloxone (7.5 mg/kg). Ethanol/BUP and ethanol/BUP/naloxone combinations significantly deepened sedation in comparison to BUP alone (P < .01) and BUP/naloxone (P < .05), respectively. Ethanol/BUP combination significantly increased the inspiratory time and decreased the minute volume in comparison to BUP alone (P < .01 and P < .01, respectively) and ethanol/BUP/naloxone (P < .05 and P < .01, respectively). Neither naloxone nor flumazenil reversed ethanol/BUP-induced sedation and respiratory depression. In the presence of ethanol, the area under the BUP concentration-time curve was significantly decreased (P < .05), BUP volume of distribution increased (P < .05) and the metabolic ratios of NBUP and norbuprenorphine-3-glucuronide increased (P < .01). In conclusion, the ethanol/BUP combination results in marked sedation and respiratory depression in the rat, prevented but not reversed by naloxone. Ethanol/BUP interactions are mainly pharmacokinetic resulting in increased NBUP production. Despite the non-reversal by naloxone and flumazenil of the effects attributed to the ethanol/BUP combination, protection provided by naloxone suggests an additional pharmacodynamic interaction.

Urine analysis of buprenorphine/norbuprenorphine/ naloxone in drugs and driving cases

It was Robinson who elucidated the active structure of morphine in 1925. Buprenorphine (2S)-2-[(5R,6R,7R,14S)-9αCyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6methoxymorphinan-7-yl]-3,3-dimethylbutan-2-ol) which is a semi-synthetic opioid. It possesses partial agonist properties acting at μ-opioid receptor site, it also possesses antagonist characteristics acting mainly on the κ-opioid receptor site [1]. Its structure is derived from thebaine, and it has a structural similarity with morphine ((5α,6α)-7,8-didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol), but has been reported to be up to 50 times more potent, with a higher affinity for μ-opioid receptors compared with other opioids, including heroin (diacetyl morphine)[2]. Historically, buprenorphine was first synthesized 1966 by John Lewis working at Reckitt and Colman (later Reckitts). Lewis had previously been a doctoral student of Sir Robert Robinson, who had elucidated the active structure of morphine in 1925 [3]. Buprenorphine (BUP) is metabolized in human beings through to the active metabolite norbuprenorphine (NBUP) via the process of N-dealkylation, performed primarily by cytochrome P450 (CYP 450) 3A4 and CYP 2D6 groups of enzymes [4]. Minor metabolites of BUP and NBUP i.e hydroxybuprenorphine and hydroxynorbuprenorphine have also been reported [5], these are believed to occur after oxidation of the tertiary butyl group on both BUP and NBUP but do not make a significant contribution to the urinary profile. Peak plasma concentration times of BUP have reported to range from 0.66 hours to 3.5 hours, its halflife (t1/2) has been reported to be as long as 44 hours [6]. NBUP the primary metabolite of buprenorphine is by nature is a weak opiate agonist and has been reported as having a potency of one quarter of buprenorphine. It has also been reported that it possesses greater respiratory depressant effects than the parent and this phenomenon may controlled not by brain based opioid receptors but those located in the lung [7]. The half-life for NBUP JOURNAL OF APPLIED BIOANALYSIS, July 2015, p. 80-88. http://dx.doi.org/10.17145/jab.15.014 (ISSN 2405-710X) Vol. 1, No. 3