Population Pharmacokinetic Model of Sublingual Buprenorphine in Neonatal Abstinence Syndrome

Salivary Therapeutic Monitoring of Buprenorphine in Neonates After Maternal Sublingual Dosing Guided by Physiologically Based Pharmacokinetic Modeling

BACKGROUND

Opioid use disorder (OUD) during pregnancy is associated with high mortality rates and neonatal opioid withdrawal syndrome (NOWS). Buprenorphine, an opioid, is used to treat OUD and NOWS. Buprenorphine active metabolite (norbuprenorphine) can cross the placenta and cause neonatal respiratory depression (EC 50 = 35 ng/mL) at high brain extracellular fluid (bECF) levels. Neonatal therapeutic drug monitoring using saliva decreases the likelihood of distress and infections associated with frequent blood sampling.

METHODS

An adult physiologically based pharmacokinetic model for buprenorphine and norbuprenorphine after intravenous and sublingual administration was constructed, vetted, and scaled to newborn and pregnant populations. The pregnancy model predicted that buprenorphine and norbuprenorphine doses would be transplacentally transferred to the newborns. The newborn physiologically based pharmacokinetic model was used to estimate the buprenorphine and norbuprenorphine levels in newborn plasma, bECF, and saliva after these doses.

RESULTS

After maternal sublingual administration of buprenorphine (4 mg/d), the estimated plasma concentrations of buprenorphine and norbuprenorphine in newborns exceeded the toxicity thresholds for 8 and 24 hours, respectively. However, the norbuprenorphine bECF levels were lower than the respiratory depression threshold. Furthermore, the salivary buprenorphine threshold levels in newborns for buprenorphine analgesia, norbuprenorphine analgesia, and norbuprenorphine hypoventilation were observed to be 22, 2, and 162 ng/mL.

CONCLUSIONS

Using neonatal saliva for buprenorphine therapeutic drug monitoring can facilitate newborn safety during the maternal treatment of OUD using sublingual buprenorphine. Nevertheless, the suitability of using adult values of respiratory depression EC 50 for newborns must be confirmed.

Development and Verification of a Full Physiologically Based Pharmacokinetic Model for Sublingual Buprenorphine in Healthy Adult Volunteers that Accounts for Nonlinear Bioavailability

Sublingual buprenorphine is used for opioid use disorder and neonatal opioid withdrawal syndrome. The study aimed to develop a full physiologically based pharmacokinetic (PBPK) model that can adequately describe dose- and formulation-dependent bioavailability of buprenorphine. Simcyp (v21.0) was used for model construction. Four linear regression models (i.e., untransformed or log transformed for dose or proportion sublingually absorbed) were explored to describe sublingual absorption of buprenorphine across dose. Published clinical trial data not used in model development were used for verification. The PBPK model's predictive performance was deemed adequate if the geometric means of ratios between predicted and observed (P/O) area under the curve (AUC), peak concentration (Cmax), and time to reach Cmax (Tmax) fell within the 1.25-fold prediction error range. Sublingual buprenorphine absorption was best described by a regression model with logarithmically transformed dose. By integrating this nonlinear absorption profile, the PBPK model adequately predicted buprenorphine pharmacokinetics (PK) following administration of sublingual tablets and solution across a dose range of 2-32 mg, with geometric mean (95% confidence interval) P/O ratios for AUC and Cmax equaling 0.99 (0.86-1.12) and 1.24 (1.09-1.40), respectively, and median (5th to 95th percentile) for Tmax equaling 1.11 (0.69-1.57). A verified PBPK model was developed that adequately predicts dose- and formulation-dependent buprenorphine PK following sublingual administration. SIGNIFICANCE STATEMENT: The physiologically based pharmacokinetic (PBPK) model developed in this study is the first to adequately predict dose- and formulation-dependent sublingual buprenorphine pharmacokinetics. Accurate prediction was facilitated by the incorporation of a novel nonlinear absorption model. The developed model will serve as the foundation for maternal-fetal PBPK modeling to predict maternal and fetal buprenorphine exposures to optimize buprenorphine treatment for neonatal opioid withdrawal syndrome.

Buprenorphine vs. morphine: impact on neonatal opioid withdrawal syndrome (NOWS) outcomes in a single center retrospective study

OBJECTIVES

To compare clinical outcomes for infants with neonatal opioid withdrawal syndrome (NOWS) treated with buprenorphine or morphine.

STUDY DESIGN

Retrospective study of infants born ≥35 weeks' gestation and admitted to the NICU for NOWS treatment between 2011 and 2022. Length of treatment, length of stay in the hospital, and the need for secondary medications were compared between buprenorphine and morphine treated neonates. Multiple regression analysis was performed, adjusting for baseline differences and confounders.

RESULTS

417 neonates were treated with morphine and 232 with buprenorphine. The buprenorphine group had shorter treatment days [-10.8 days; 95% CI: -8.08 to -13.53] and shorter hospital stay [-11.8 days; 95% CI: -8.83 to -14.78]. The buprenorphine group was no more likely to receive phenobarbital or clonidine (26% vs. 29%).

CONCLUSION

In this large single-center study, buprenorphine was associated with shorter lengths of treatment and hospital stay in the treatment of NOWS compared to morphine.

Physiologically-Based Pharmacokinetic Modeling to Investigate the Effect of Maturation on Buprenorphine Pharmacokinetics in Newborns with Neonatal Opioid Withdrawal Syndrome

Neonatal opioid withdrawal syndrome (NOWS) is a major public health concern whose incidence has paralleled the opioid epidemic in the United States. Sublingual buprenorphine is an emerging treatment for NOWS, but given concerns about long-term adverse effects of perinatal opioid exposure, precision dosing of buprenorphine is needed. Buprenorphine pharmacokinetics (PK) in newborns, however, is highly variable. To evaluate underlying sources of PK variability, a neonatal physiologically-based pharmacokinetic (PBPK) model of sublingual buprenorphine was developed using Simcyp (version 19.1). The PBPK model included metabolism by cytochrome P450 (CYP) 3A4, CYP2C8, UDP-glucuronosyltransferase (UGT) 1A1, UGT1A3, UGT2B7, and UGT2B17, with additional biliary excretion. Maturation of metabolizing enzymes was incorporated, and default CYP2C8 and UGT2B7 ontogeny profiles were updated according to recent literature. A biliary clearance developmental profile was outlined using clinical data from neonates receiving sublingual buprenorphine as NOWS treatment. Extensive PBPK model validation in adults demonstrated good predictability, with geometric mean (95% confidence interval (CI)) predicted/observed ratios (P/O ratios) of area under the curve from zero to infinity (AUC_0-∞ ), peak concentration (C_max ), and time to reach peak concentration (T_max ) equaling 1.00 (0.74-1.33), 1.04 (0.84-1.29), and 0.95 (0.72-1.26), respectively. In neonates, the geometric mean (95% CI) P/O ratio of whole blood concentrations was 0.75 (95% CI 0.64-0.87). PBPK modeling and simulation demonstrated that variability in biliary clearance, sublingual absorption, and CYP3A4 abundance are likely important drivers of buprenorphine PK variability in neonates. The PBPK model could be used to guide development of improved buprenorphine starting dose regimens for the treatment of NOWS.

Integrated Review of the Assessment of Newborns With Neonatal Abstinence Syndrome

OBJECTIVE

To critically review and summarize current knowledge regarding the assessment of newborns with neonatal abstinence syndrome (NAS).

DATA SOURCES

We searched the following databases for articles on the assessment of newborns with NAS that were published in English between January 2014 and June 2020: PubMed, CINAHL, and PsycINFO. Keywords and Medical Subject Heading terms used to identify relevant research articles included neonatal abstinence syndrome; Finnegan Scale; eat, sleep, console; epigenetics; genetics; pharmacokinetics; and measurement. We independently reviewed articles for inclusion.

STUDY SELECTION

We retrieved 435 articles through database searches and 17 through manual reference searches; 31 articles are included in the final review. Excluded articles were duplicates, not relevant to NAS, qualitative studies, and/or of low quality.

DATA EXTRACTION

We used the methodology of Whittemore and Knafl to guide this integrative review. We extracted and organized data under the following headings: author, year and country, purpose, study design, participants, measurement, biomarker (if applicable), results, limitations, recommendations, and intervention.

DATA SYNTHESIS

The Finnegan Neonatal Abstinence Scale is the most widely used instrument to measure symptoms of NAS in newborns, although it is very subjective. Recently, there has been a transition from the Finnegan Neonatal Abstinence Scale to the eat, sleep, console method, which consists of structured assessment and intervention and has been shown to decrease length of hospital stay and total opioid treatment dose. Researchers examined biomarkers of NAS, including genetic markers and autonomic nervous system responses, on the variation in incidence and differential severity of NAS. In the included articles, women with opioid use disorder who were treated with naltrexone during pregnancy gave birth to newborns without NAS diagnoses. However, most women who were treated with buprenorphine gave birth to newborns with NAS diagnoses.

CONCLUSION

NAS negatively affects newborns in a multitude of ways, and the objective assessment and measurement of the newborn's response to withdrawal remains understudied and needs further investigation.

Pharmacometric dose optimization of buprenorphine in neonatal opioid withdrawal syndrome

Results from Blinded Buprenorphine OR Neonatal morphine solution (BBORN), a previous phase III trial in infants with neonatal opioid withdrawal syndrome (NOWS), demonstrated that sublingual buprenorphine resulted in a shorter duration of treatment and shorter length of hospital stay than the comparator, oral morphine. Objectives of Buprenorphine Pharmacometric Open Label Research study of Drug Exposure (BPHORE), a new trial with buprenorphine in a similar population, were to (1) optimize initial dose, up-titration to achieve symptom control and weaning steps of pharmacologic treatment and (2) investigate safety of the revised regimen. A pharmacodynamic model linked buprenorphine exposure to NOWS symptom scores. Adaptive dose regimens were simulated using BBORN results to compare dosing regimens for times to stabilization, weaning, and cessation. A clinical trial using model informed doses (BPHORE), was conducted. Simulations indicated benefits in time to stabilization and weaning when up-titration rates increased to 30%. Stabilization time was not greatly impacted by the starting dose. Time to wean and time to cessation were dose dependent. A weaning rate of 25% shortened time to cessation. Ten infants were enrolled in BPHORE using buprenorphine starting dose of 24 µg/kg/day, 33% titration, and 15% wean rate. Five subjects required adjuvant therapy. Half-maximal effective concentration (EC₅₀ ) values indicated maximum buprenorphine doses did not generate maximal effect size, suggesting potential efficacy of a further increased dose if a goal was to reduce the use of adjunct agents. Simulations indicated that further benefits can be gained by increasing starting doses of buprenorphine and increasing wean rates. Use of a model-based analysis to provide focused guidelines for care can be used with goals of reducing treatment time and hospital stays in infants with NOWS.

Using buprenorphine to treat neonatal abstinence syndrome: a quality improvement study

OBJECTIVE

To assess if treating neonatal abstinence syndrome (NAS) with sublingual buprenorphine (SLB) would decrease the mean duration of therapy (DOT) and length of birth hospital stay (LOS).

STUDY DESIGN

Conducted at a tertiary hospital with >6000 annual deliveries and a 2% incidence of NAS, a quality improvement study using plan-do-study-act (PDSA) cycles were utilized. Outcomes were measured using statistical process control (SPC) charts.

RESULTS

All NAS patients were treated with SLB, no adverse reactions were reported and the need for an adjunctive agent was static. SPC charts demonstrated decreased variability and special cause variation indicating a reduction in both DOT (from 14.5 to 8.5 days) and LOS (from 18.5 to 13 days).

Clinical pharmacology and dosing regimen optimization of neonatal opioid withdrawal syndrome treatments

In this paper, we review the management of neonatal opioid withdrawal syndrome (NOWS) and clinical pharmacology of primary treatment agents in NOWS, including morphine, methadone, buprenorphine, clonidine, and phenobarbital. Pharmacologic treatment strategies in NOWS have been mostly empirical, and heterogeneity in dosing regimens adds to the difficulty of extrapolating study results to broader patient populations. As population pharmacokinetics (PKs) of pharmacologic agents in NOWS become more well‐defined and knowledge of patient‐specific factors affecting treatment outcomes continue to accumulate, PK/pharmacodynamic modeling and simulation will be powerful tools to aid the design of optimal dosing regimens at the patient level. Although there is an increasing number of clinical trials on the comparative efficacy of treatment agents in NOWS, here, we also draw attention to the importance of optimizing the dosing regimen, which can be arguably equally important at identifying the optimal treatment agent.

Opioid Treatment for Neonatal Opioid Withdrawal Syndrome: Current Challenges and Future Approaches

Chronic intrauterine exposure to psychoactive drugs often results in neonatal opioid withdrawal syndrome (NOWS). When nonpharmacologic measures are insufficient in controlling NOWS, morphine, methadone, and buprenorphine are first-line medications commonly used to treat infants with NOWS because of in utero exposure to opioids. Research suggests that buprenorphine may be the leading drug therapy used to treat NOWS when compared with morphine and methadone. Currently, there are no consensus or standardized treatment guidelines for medications prescribed for NOWS. Opioids used to treat NOWS exhibit large interpatient variability in pharmacokinetics (PK) and pharmacodynamic (PD) response in neonates. Organ systems undergo rapid maturation after birth that may alter drug disposition and exposure for any given dose during development. Data regarding the PK and PD of opioids in neonates are sparse. Pharmacometric methods such as physiologically based pharmacokinetic and population pharmacokinetic modeling can be used to explore factors predictive of some of the variability associated with the PK/PD of opioids in newborns. This review discusses the utility of pharmacometric techniques for enhancing precision dosing in infants requiring opioid treatment for NOWS. Applying these approaches may contribute to optimizing the outcome by reducing cumulative drug exposure, mitigating adverse drug effects, and reducing the burden of NOWS in neonates.

Pharmacokinetic Characterization and External Evaluation of a Quantitative Framework of Sublingual Buprenorphine in Patients with an Opioid Disorder in Puerto Rico

Background: The aim of this analysis was to characterize the pharmacokinetics (PK) of sublingual buprenorphine (BUP) and its metabolites (buprenorphine glucuronide; BUP-g, norbuprenorphine; Nor-BUP, and norbuprenorphine glucuronide; Nor-BUP-g) in opioid use disorder (OUD) patients in Puerto Rico (PR) as a first step of evidence-based BUP dosing strategies in this population. Methods: BUP and metabolites concentrations were measured from 0 to 8 h after the administration of sublingual buprenorphine/naloxone films in 12 stable OUD subjects. Results: PK non-compartmental characteristics showed considerable variability in parameters between the subjects over the 8-h sampling time (t_max = 1.5 ± 0.7 h, C_o = 1.6 ± 1.4 ng/mL, C_max= 7.1 ± 6 ng/mL, and AUC_0–8h = 26.8 ± 17.8 h·ng/mL). Subjects had a significantly higher tendency towards CYP-mediated N-demethylation, with the AUC_0–8h ratios of the molar concentrations of [Nor-BUP + Nor-BUP-g] to BUP being (3.4 ± 1.9) significantly higher compared with BUP-g to BUP (0.19 ± 0.2). A two-compartment population-PK model with linear absorption (k_a = 2.54 h⁻¹), distribution (k₁₂= 2.34 h⁻¹, k₁₄ = 1.29 h⁻¹), metabolism (k₂₄ = 1.28 × 10⁻¹ h⁻¹, k₂₃ = 6.43 × 10⁻² h⁻¹, k₃₅ = 1.23 × 10⁻¹ h⁻¹, k₄₅ = 8.73 × 10⁻¹ h⁻¹), and elimination (k₃₀ = 3.81 × 10⁻³ h⁻¹, k₅₀ = 1.27 × 10⁻¹ h⁻¹) adequately described the time-course of BUP and its metabolites, which has been externally validated using published data. Conclusions: Although limited in sampling time and number of recruited subjects, this study presents specific BUP PK characteristics that evidenced the need for additional PK studies and subsequent modeling of the data for the development of evidence-based dosing approaches in Puerto Rico.

Pharmacotherapy of neonatal opioid withdrawal syndrome: a review of pharmacokinetics and pharmacodynamics

INTRODUCTION

Neonatal opioid withdrawal syndrome (NOWS) often arises in infants born to mothers who used opioids during pregnancy. Morphine, methadone, and buprenorphine are the most common first-line treatments, whereas clonidine and phenobarbital are generally reserved for adjunctive therapy. These drugs exhibit substantial pharmacokinetic (PK) and pharmacodynamic (PD) variability. Current pharmacological treatments for NOWS are based on institutional protocols and largely rely on empirical treatment of patient symptoms.

AREAS COVERED

This article reviews the PK/PD of NOWS pharmacotherapies with a focus on the implication of physiological development and maturation. Body size-standardized clearance is consistently low in neonates, except for methadone. This can be ascribed to underdeveloped metabolic and elimination pathways. The effects of pharmacogenetics have been clarified especially for morphine. The PK/PD relationship of medications used in the treatment of NOWS is generally understudied.

EXPERT OPINION

Providing an appropriate opioid dose in neonates is challenging. Advancements in quantitative pharmacology and PK/PD modeling approaches facilitate identification of key factors driving PK/PD variability and characterization of exposure-response relationships. PK/PD model-informed simulations have been widely employed to define age-appropriate pediatric dosing regimens. The model-informed approach holds promise to aid more rational use of medications in the treatment of NOWS.

Hospital Care of Opioid-Exposed Newborns: Clinical and Psychosocial Challenges

In the past two decades, the incidence of neonatal abstinence syndrome (NAS) has risen fivefold, mirroring the rise of opioid use disorder (OUD) among pregnant women. The resulting increases in length of stay and neonatal intensive care utilization are associated with higher hospital costs, particularly among Medicaid-financed deliveries. Pregnant women with OUD require comprehensive medical and psychosocial evaluation and management; this combined with medication-assisted treatment is critical to optimize maternal and newborn outcomes. Multidisciplinary collaboration and standardized approaches to screening for intrauterine opioid exposure, evaluation and treatment of NAS, and discharge planning are important for clinical outcomes and may improve maternal experience of care.

Physiologic Indirect Response Modeling to Describe Buprenorphine Pharmacodynamics in Newborns Treated for Neonatal Opioid Withdrawal Syndrome

BACKGROUND AND OBJECTIVE

Buprenorphine has been shown to be effective in treating infants with neonatal opioid withdrawal syndrome. However, an evidence-based buprenorphine dosing strategy has not been established in the treatment of neonatal opioid withdrawal syndrome because of a lack of exposure-response data. The aim of this study was to develop an integrated pharmacokinetic and pharmacodynamic model to predict buprenorphine treatment outcomes in newborns with neonatal opioid withdrawal syndrome.

METHODS

Clinical data were obtained from 19 newborns with a median (range) gestational age of 37 (34-41) weeks enrolled in a pilot pharmacokinetic study of buprenorphine. Sparse blood sampling, comprising three specimens obtained around the second dose of buprenorphine, was performed using heel sticks with dried blood spot technology. Standardized neonatal opioid withdrawal syndrome severity scores (Finnegan scores) were collected every 3-4 h based on symptoms by bedside nursing staff. Mean Finnegan scores were used as a pharmacodynamic marker in the exposure-response modeling. The blood concentration-Finnegan score relationship was described using a physiologic indirect response model with inclusion of natural disease remission.

RESULTS

A total of 52 buprenorphine blood concentrations and 780 mean Finnegan scores were available for the pharmacokinetic/pharmacodynamic modeling and exposure-response analysis. A one-compartment model with first-order absorption adequately described the pharmacokinetic data. The buprenorphine blood concentration at 50% of maximum effect for the inhibition of disease progression was 0.77 ng/mL (95% confidence interval 0.32-1.2). The inclusion of natural disease remission described as a function of postnatal age significantly improved the model fit.

CONCLUSIONS

A buprenorphine pharmacokinetic/pharmacodynamic model was successfully developed. The model could facilitate model-informed optimization of the buprenorphine dosing regimen in the treatment of neonatal opioid withdrawal syndrome.

Opioids: A Review of Pharmacokinetics and Pharmacodynamics in Neonates, Infants, and Children

Pain management in the pediatric population is complex for many reasons. Mild pain is usually managed quite well with oral acetaminophen or ibuprofen. Situations involving more severe pain often require the use of an opioid, which may be administered by many different routes, depending on clinical necessity. Acute and chronic disease states, as well as the constantly changing maturational process, produce unique challenges at every level of pediatrics in dosing and management of all medications, especially with regard to high-risk opioids. Although there has been significant progress in the understanding of opioid pharmacokinetics and pharmacodynamics in neonates, infants, children, and adolescents, somewhat limited data exist from which necessary information, concerning the safe and effective use of these agents, may be drawn. The evidence here provided is intended to be helpful in directing the practitioner to patient-specific reasons for preferring one opioid over another. As our knowledge of opioids and their effects has grown, it has become clear that older medications like codeine and meperidine (pethidine) have very limited use in pediatrics. This review provides pharmacokinetic and pharmacodynamic evidence on the currently available opioids: morphine, fentanyl (and derivatives), codeine, meperidine, oxycodone, hydrocodone, hydromorphone, methadone, buprenorphine, butorphanol, nalbuphine, pentazocin, ketobemidone, tramadol, piritramide, naloxone and naltrexone. Morphine, being the most studied opioid analgesic, is the standard against which all others are compared. Pharmacokinetic parameters of morphine that have been found in neonates, i.e., higher volume of distribution, immature metabolic processes that develop at various rates, elimination that is variable based on age and weight, as well as treated and untreated disease processes, are an example of all opioids in the population discussed in this review. Outside the premature and neonatal population, the use of opioids in infants, children, and adolescents quickly begins to resemble the established values found in adults. As such, the concerns (risks) of these medications become comparable to those seen in adults.

Pharmacological and non-pharmacological treatments for the Neonatal Abstinence Syndrome (NAS)

Neonatal abstinence syndrome is defined by signs and symptoms of withdrawal that infants develop after intrauterine maternal drug exposure. All infants with documented in utero opioid exposure, or a high pre-test probability of exposure should have monitoring with a standard assessment instrument such as a Finnegan Score. A Finnegan score of >8 is suggestive of opioid exposure, even in the absence of declared use during pregnancy. At least half of infants in most locales can be treated without the use of pharmacologic means. For this reason, symptom scores will drive the decision for pharmacologic therapy. Nevertheless, all infants, regardless of initial manifestations, should be first be managed with non-pharmacologic approaches which in turn, should not be considered as the sole alternative to drug therapy, but rather, as the base upon which all patients are treated. Those who continue to have symptoms despite supportive care should be pharmacologically treated, which in the most severe cases, is life-saving.

Buprenorphine for the Treatment of Neonatal Abstinence Syndrome

Objective: To summarize the available data for using buprenorphine in neonatal abstinence syndrome and discuss these data in context of the current standard of care therapies, oral morphine and oral methadone. Data Sources: A literature search was conducted using PubMed (1949-May 2018) and EMBASE (1980-May 2018). Combinations of the search terms “buprenorphine,” “neonatal,” and “neonatal abstinence syndrome” were used. Study Selection and Data Extraction: All full-length, English-language studies were included in this review. Data Synthesis: A total of 4 studies were included in this review including 1 retrospective cohort study, 2 prospective single-center open-label randomized trials, and 1 prospective single-center, double-blind study. Oral morphine was the comparator in 3 studies, and oral methadone was the comparator in one. Buprenorphine was associated with a significant reduction in duration of treatment in 3 of the 4 studies and was associated with a significant reduction in duration of hospital stay in 3 of the 4 studies. In the randomized, double-blinded trial, buprenorphine had a significantly reduced duration of treatment (15 vs 28 days, P < .001) and duration of hospital stay (21 vs 33 days, P < .001). The requirement of adjunct treatment was similar between groups in all 4 studies, and buprenorphine did not have any significant adverse reactions in comparison with morphine and methadone. Conclusions: Buprenorphine appears to be a safe option for treating neonatal abstinence syndrome that is potentially superior to the current standard of care therapies with respect to duration of treatment and hospital length of stay.

Treating Chronic Pain: An Overview of Clinical Studies Centered on the Buprenorphine Option

The buprenorphine receptor binding profile is unique in that it binds to all three major opioid receptors (mu, kappa, delta), and also binds to the orphan-like receptor, the receptor for orphanin FQ/nociceptin, with lower affinity. Within the mu receptor group, buprenorphine analgesia in rodents is dependent on the recently discovered arylepoxamide receptor target in brain, which involves a truncated 6-transmembrane mu receptor gene protein, distinguishing itself from morphine and most other mu opioids. Although originally designed as an analgesic, buprenorphine has mainly been used for opioid maintenance therapy and only now is increasingly recognized as an effective analgesic with an improved therapeutic index relative to certain potent opioids. Albeit a second-, third-, or fourth-line analgesic, buprenorphine is a reasonable choice in certain clinical situations. Transdermal patches and buccal film formulations are now commercially available as analgesics. This review discusses buprenorphine pharmacodynamics and pharmacokinetics, use in certain populations, and provides a synopsis of systematic reviews and randomized analgesic trials. We briefly discuss postoperative management in patients receiving buprenorphine maintenance therapy, opioid equivalence to buprenorphine, rotations to buprenorphine from other opioids, and clinical relevance of buprenorphine-related QTc interval changes.

The Pharmacokinetics and Pharmacodynamics of Buprenorphine in Neonatal Abstinence Syndrome

Neonatal abstinence syndrome (NAS) is a condition affecting newborns that are exposed to an opioid in utero. In a randomized, controlled trial assessing the efficacy of buprenorphine and morphine in NAS, blood samples were analyzed from a subset of patients receiving buprenorphine along with NAS scores. The data were used to validate and adapt an existing model of buprenorphine in neonates and to identify relationships between buprenorphine or norbuprenorphine pharmacokinetics (PK) and efficacy or safety. The time to NAS stabilization was found to decrease with increasing buprenorphine exposure. This pharmacokinetic-pharmacodynamic (PK-PD) relationship was able to be quantified and adequately described with a mathematical model. The findings confirm a previous PK model of buprenorphine and extend the model to describe the PK of norbuprenorphine and to identify a novel PK-PD relationship of buprenorphine in NAS. This model will allow optimization of dosing strategies in future clinical trials.

Treating Women Who Are Pregnant and Parenting for Opioid Use Disorder and the Concurrent Care of Their Infants and Children: Literature Review to Support National Guidance

OBJECTIVES

The prevalence of opioid use disorder (OUD) during pregnancy is increasing. Practical recommendations will help providers treat pregnant women with OUD and reduce potentially negative health consequences for mother, fetus, and child. This article summarizes the literature review conducted using the RAND/University of California, Los Angeles Appropriateness Method project completed by the US Department of Health and Human Services Substance Abuse and Mental Health Services Administration to obtain current evidence on treatment approaches for pregnant and parenting women with OUD and their infants and children.

METHODS

Three separate search methods were employed to identify peer-reviewed journal articles providing evidence on treatment methods for women with OUD who are pregnant or parenting, and for their children. Identified articles were reviewed for inclusion per study guidelines and relevant information was abstracted and summarized.

RESULTS

Of the 1697 articles identified, 75 were included in the literature review. The perinatal use of medication for addiction treatment (MAT, also known as medication-assisted treatment), either methadone or buprenorphine, within comprehensive treatment is the most accepted clinical practice, as withdrawal or detoxification risks relapse and treatment dropout. Medication increases may be needed with advancing pregnancy, and are not associated with more severe neonatal abstinence syndrome (NAS). Switching medication prenatally is usually not recommended as it can destabilize opioid abstinence. Postnatally, breastfeeding is seen as beneficial for the infant for women who are maintained on a stable dose of opioid agonist medication. Less is known about ideal pain management and postpartum dosing regimens. NAS appears generally less severe following prenatal exposure to buprenorphine versus methadone. Frontline NAS medication treatments include protocol-driven methadone and morphine dosing in the context of nonpharmacological supports.

CONCLUSIONS

Women with OUD can be treated with methadone or buprenorphine during pregnancy. NAS is an expected and manageable condition. Although research has substantially advanced, opportunities to guide future research to improve maternal and infant outcomes are provided.

Buprenorphine in Neonatal Abstinence Syndrome

Infants exposed in utero to opioids will demonstrate a withdrawal syndrome known as neonatal abstinence syndrome (NAS). Buprenorphine is a long-acting opioid with therapeutic use in medication-assisted treatment of opioid dependency in adults and adolescents. Emerging data from clinical trials and treatment cohorts demonstrate the efficacy and safety of sublingual buprenorphine for those infants with NAS who require pharmacologic treatment. Pharmacometric modeling will assist in defining the exposure-response relationships and facilitate dose optimization.

Population pharmacokinetics of exendin-(9-39) and clinical dose selection in patients with congenital hyperinsulinism

AIMS

Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycaemia in infants and children. Exendin-(9-39), an inverse glucagon-like peptide 1 (GLP-1) agonist, is a novel therapeutic agent for HI that has demonstrated glucose-raising effect. We report the first population pharmacokinetic (PopPK) model of the exendin-(9-39) in patients with HI and propose the optimal dosing regimen for future clinical trials in neonates with HI.

METHODS

A total of 182 pharmacokinetic (PK) observations from 26 subjects in three clinical studies were included for constructing the PopPK model using first order conditional estimation (FOCE) with interaction method in nonlinear mixed-effects modelling (NONMEM). Exposure metrics (area under the curve [AUC] and maximum plasma concentration [C_max ]) at no observed adverse effect levels (NOAELs) in rats and dogs were determined in toxicology studies.

RESULTS

Observed concentration-time profiles of exendin-(9-39) were described by a linear two-compartmental PK model. Following allometric scaling of PK parameters, age and creatinine clearance did not significantly affect clearance. The calculated clearance and elimination half-life for adult subjects with median weight of 69 kg were 11.8 l h^-1 and 1.81 h, respectively. The maximum recommended starting dose determined from modelling and simulation based on the AUC_0-last at the NOAEL and predicted AUC_0-inf using the PopPK model was 27 mg kg^-1  day^-1 intravenously.

CONCLUSIONS

This is the first study to investigate the PopPK of exendin-(9-39) in humans. The final PopPK model was successfully used with preclinical toxicology findings to propose the optimal dosing regimen of exendin-(9-39) for clinical studies in neonates with HI, allowing for a more targeted dosing approach to achieve desired glycaemic response.

Pharmacotherapy for Neonatal Abstinence Syndrome: Choosing the Right Opioid or No Opioid at All

Neonatal abstinence syndrome (NAS) from in utero opioid exposure has reached epidemic levels in the United States. Although nonpharmacologic therapies form the foundation of care, many neonates require pharmacotherapy. Morphine represents the most widely used first-line agent and effectively treats the symptoms of withdrawal. However, methadone or buprenorphine may facilitate earlier discharge. Although phenobarbital is traditionally used when opioids fail, clonidine may be a more appropriate adjunctive agent to minimize negative neurodevelopmental impact. Consideration of the available data allows hospitals to generate effective pharmacologic strategies to manage NAS while further research continues.

Buprenorphine for the Treatment of the Neonatal Abstinence Syndrome

BACKGROUND

Current pharmacologic treatment of the neonatal abstinence syndrome with morphine is associated with a lengthy duration of therapy and hospitalization. Buprenorphine may be more effective than morphine for this indication.

METHODS

In this single-site, double-blind, double-dummy clinical trial, we randomly assigned 63 term infants (≥37 weeks of gestation) who had been exposed to opioids in utero and who had signs of the neonatal abstinence syndrome to receive either sublingual buprenorphine or oral morphine. Infants with symptoms that were not controlled with the maximum dose of opioid were treated with adjunctive phenobarbital. The primary end point was the duration of treatment for symptoms of neonatal opioid withdrawal. Secondary clinical end points were the length of hospital stay, the percentage of infants who required supplemental treatment with phenobarbital, and safety.

RESULTS

The median duration of treatment was significantly shorter with buprenorphine than with morphine (15 days vs. 28 days), as was the median length of hospital stay (21 days vs. 33 days) (P<0.001 for both comparisons). Adjunctive phenobarbital was administered in 5 of 33 infants (15%) in the buprenorphine group and in 7 of 30 infants (23%) in the morphine group (P=0.36). Rates of adverse events were similar in the two groups.

CONCLUSIONS

Among infants with the neonatal abstinence syndrome, treatment with sublingual buprenorphine resulted in a shorter duration of treatment and shorter length of hospital stay than treatment with oral morphine, with similar rates of adverse events. (Funded by the National Institute on Drug Abuse; BBORN ClinicalTrials.gov number, NCT01452789 .).

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Naloxone and Metabolites Quantification in Cord Blood of Prenatally Exposed Newborns and Correlations with Maternal Concentrations

Objective To quantify naloxone and metabolite concentrations in newborns prenatally exposed to sublingual buprenorphine/naloxone and to correlate neonatal and maternal metabolite concentrations. Methods This is a prospective observational cohort study. Eleven pregnant women treated for opioid use disorder with sublingual buprenorphine/naloxone were enrolled. Maternal and newborn blood was collected and analyzed for naloxone, buprenorphine, and metabolites via liquid chromatography tandem mass spectrometry. Descriptive statistics and correlation coefficients were utilized to analyze data. Results Maternal daily naloxone and buprenorphine doses were 1 to 5 mg and 4 to 20 mg, respectively; the mean (standard deviation) time from medication until delivery was 9.9 (4.3) hours. Naloxone was below the limits of quantification (LOQ) in five infants and six mothers with a range of less than LOQ to 0.3 μg/L. There was a strong positive correlation between maternal and newborn naloxone concentrations: Spearman's ρ = 0.89 (p < 0.01). There were strong positive correlations between maternal and neonatal assays for the buprenorphine analyte concentrations: buprenorphine ρ = 0.88 (p < 0.01), norbuprenorphine ρ = 0.71 (p = 0.01), and norbuprenorphine-glucuronide ρ = 0.98 (p < 0.01), but not for buprenorphine-glucuronide, ρ = 0.53 (p = 0.10). Conclusion Naloxone and buprenorphine are transferred to the fetus during prenatal exposure to maternal sublingual buprenorphine/naloxone. The quantity of naloxone transferred from maternal circulation is minimal and highly correlated with maternal concentrations.

Neonatal abstinence syndrome: Pharmacologic strategies for the mother and infant

Opioid use in pregnancy has increased dramatically over the past decade. Since prenatal opioid use is associated with numerous obstetrical and neonatal complications, this now has become a major public health problem. In particular, in utero opioid exposure can result in neonatal abstinence syndrome (NAS) which is a serious condition characterized by central nervous system hyperirritability and autonomic nervous system dysfunction. The present review seeks to define current practices regarding the approach to the pregnant mother and neonate with prenatal opiate exposure. Although the cornerstone of prenatal management of opioid dependence is opioid maintenance therapy, the ideal agent has yet to be definitively established. Pharmacologic management of NAS is also highly variable and may include an opioid, barbiturate, and/or α-agonist. Genetic factors appear to be associated with the incidence and severity of NAS. Establishing pharmacogenetic risk factors for the development of NAS has the potential for creating opportunities for "personalized genomic medicine" and novel, individualized therapeutic interventions.

A Cohort Comparison of Buprenorphine versus Methadone Treatment for Neonatal Abstinence Syndrome

OBJECTIVES

To compare the duration of opioid treatment and length of stay among infants treated for neonatal abstinence syndrome (NAS) by using a pilot buprenorphine vs conventional methadone treatment protocol.

STUDY DESIGN

This retrospective cohort analysis evaluated infants who received pharmacotherapy for NAS at 6 hospitals in Southwest Ohio from January 2012 through August 2014. A single neonatology provider group used a standardized methadone protocol across all 6 hospitals. However, at one of the sites, infants were managed with a buprenorphine protocol unless they had experienced chronic in utero exposure to methadone. Linear mixed models were used to calculate adjusted mean duration of opioid treatment and length of inpatient hospitalization with 95% CIs in infants treated with oral methadone compared with sublingual buprenorphine. The use of adjunct therapy was examined as a secondary outcome.

RESULTS

A total of 201 infants with NAS were treated with either buprenorphine (n = 38) or methadone (n = 163) after intrauterine exposure to short-acting opioids or buprenorphine. Buprenorphine therapy was associated with a shorter course of opioid treatment of 9.4 (CI 7.1-11.7) vs 14.0 (12.6-15.4) days (P < .001) and decreased hospital stay of 16.3 (13.7-18.9) vs 20.7 (19.1-22.2) days (P < .001) compared with methadone therapy. No difference was detected in the use of adjunct therapy (23.7% vs 25.8%, P = .79) between treatment groups.

CONCLUSION

The choice of pharmacotherapeutic agent is an important determinant of hospital outcomes in infants with NAS. Sublingual buprenorphine may be superior to methadone for management of NAS in infants with select intrauterine opioid exposures.