Opioid Metabolism and Effects of Cytochrome P450

Are carfentanil and acrylfentanyl naloxone resistant?

The rapid rise in deaths since 2012 due to opioid poisoning is correlated with the proliferation of potent synthetic opioid agonists such as fentanyl, acrylfentanyl, and carfentanil. The efficacy of frontline antidotes such as naloxone in reversing such poisoning events has been questioned, and the possibility of naloxone-resistant synthetic opioids has been raised. In this manuscript, we applied in vitro techniques to establish the median effective inhibitory concentrations for fentanyl, acrylfentanyl, and carfentanil and subsequently evaluate naloxone's ability to reverse agonist-receptor interactions.

Opioid trail: Tracking contributions to opioid use disorder from host genetics to the gut microbiome

Opioid use disorder (OUD) is a worldwide public health crisis with few effective treatment options. Traditional genetics and neuroscience approaches have provided knowledge about biological mechanisms that contribute to OUD-related phenotypes, but the complexity and magnitude of effects in the brain and body remain poorly understood. The gut-brain axis has emerged as a promising target for future therapeutics for several psychiatric conditions, so characterizing the relationship between host genetics and the gut microbiome in the context of OUD will be essential for development of novel treatments. In this review, we describe evidence that interactions between host genetics, the gut microbiome, and immune signaling likely play a key role in mediating opioid-related phenotypes. Studies in humans and model organisms consistently demonstrated that genetic background is a major determinant of gut microbiome composition. Furthermore, the gut microbiome is susceptible to environmental influences such as opioid exposure. Additional work focused on gene by microbiome interactions will be necessary to gain improved understanding of their effects on OUD-related behaviors.

Accelerated Fentanyl Metabolism During Pregnancy and Impact on Prenatal Drug Testing

OBJECTIVE

To evaluate the metabolic pattern of illicit fentanyl in a sample of pregnant patients with opioid use disorder. Fentanyl pharmacokinetics during pregnancy are currently understudied yet the interpretation of a fentanyl immunoassay during pregnancy has significant implications on maternal legal custody and child welfare. Through this medical-legal lens, we demonstrate the utility of an emerging metric, the metabolic ratio, for accurate analysis of fentanyl pharmacokinetics during pregnancy.

METHODS

We conducted a retrospective cohort analysis using the electronic medical records of 420 patients receiving integrated prenatal and opioid use disorder care at a large urban safety net hospital. Data related to maternal health and substance use were collected for each subject. The metabolic ratio was calculated for each subject to measure their rate of metabolism. The sample's (n = 112) metabolic ratios were compared with a large non-pregnant sample (n = 4366).

RESULTS

The metabolic ratios of our pregnant sample were significantly (p = .0001) higher than the metabolic ratios of our non-pregnant sample, indicating that the rate of conversion to the major metabolite was faster in pregnant people. The effect size for this difference between the pregnant and non-pregnant sample was large (d = 0.86).

CONCLUSIONS FOR PRACTICE

Our findings characterize the unique metabolic pattern of fentanyl in pregnant people who use opioids, providing guidance for institutional policies around fentanyl drug testing. Additionally, our study warns of misinterpretation of toxicology results and stresses the importance of physician advocacy on behalf of pregnant women who use illicit opioids.

N-substituted tetrahydro-beta-carboline as mu-opioid receptors ligands: in silico study; molecular docking, ADMET and molecular dynamics approach

Manipulating intracellular signals by interaction with transmembranal G-protein-coupled receptors (GPCRs) is the way of action of more than 30% of available medicines. Designing molecules against GPCRs is most challenging due to their flexible binding orthosteric and allosteric pockets, a property that lead to different mode and extent of activation of intracellular mediators. Here, in the current study we aimed to design N-substituted tetrahydro-beta-carbolines (THβC's) targeting Mu Opioid Receptors (MORs). We performed ligand docking study for reference and designed compounds against active and inactive states of MOR, as well as the active state bound to intracellular mediator of Gi. The reference compounds include 40 known agonists and antagonists, while the designed compounds include 25,227 N-substituted THβC analogues. Out of the designed compounds, 15 compounds were comparatively having better extra precision (XP) Gscore and were analyzed for absorption, distribution, metabolism, and excretion-toxicity (ADMET) properties, drug-likness, and molecular dynamic (MD) simulation. The results showed that N-substituted tetrahydro-beta-carbolines with and without C6-methoxy group substitutions (THBC/6MTHBC) analogues of A1/B1 and A9/B9 have relatively acceptable affinity and within pocket-stability toward MOR compared to the reference compounds of morphine (agonist) and naloxone (antagonist). Moreover, the designed analogues interact with key residue within the binding pocket of Asp 147 that is reported to be involved in receptor activation. In conclusion, the designed THBC analogues represent a good starting point for designing opioid receptor ligands other than morphinan scaffold, that have good synthetic accessibility which promotes feasible structural manipulation to tailor pharmacological effects with minimal side effects. Workflow rational in the discovery of potential Mu Opioid Receptor ligands.

Gaps in Evidence-based Treatment of Concurrent Attention Deficit Hyperactivity Disorder and Opioid Use Disorder: A Scoping Review

OBJECTIVES

To describe the effectiveness of medications for the treatment of opioid use disorder (OUD) and attention deficit/hyperactivity disorder (ADHD).

DATA SOURCES

Literature search of PubMed, Embase, Web of Science, CINAHL, Medline, PsycINFO, and Google Scholar was performed for studies published from inception to October 25, 2022.

STUDY SELECTION AND DATA EXTRACTION

Studies were included if patients were diagnosed with OUD and ADHD and had pharmacotherapy for either condition. Abstracts, commentaries, reviews, case reports, case series, non-English articles, and animal studies were omitted.

DATA SYNTHESIS

This review found 18 studies. Treatment of ADHD was evaluated for impact on ADHD and OUD outcomes, while treatment of OUD was evaluated for OUD-related outcomes. Outcomes assessed included markers for symptom intensity, adherence, and treatment failure. While results were mixed, treatment of ADHD was largely associated with improvements in ADHD severity and retention in OUD treatment programs. ADHD severity was associated with higher rates of illicit substance abuse and worse OUD-related outcomes. It could not be determined which medications for treatment of OUD should be prioritized.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review summarized key findings from studies that treated ADHD or OUD among dually diagnosed patients and highlighted methodological considerations for future research.

CONCLUSIONS

Treatment of ADHD is warranted among patients with OUD and ADHD to improve retention in OUD treatment programs and reduce illicit substance abuse. Pharmacotherapy for the treatment of ADHD or OUD should continue to be determined based on patients' characteristics and the capabilities of the treatment program.

Pharmacogenomics of Opioid Treatment for Pain Management

Pain affects approximately 100 million Americans. Pain harms quality of life and costs patients billions of dollars per year. Clinically, nonpharmacologic and pharmacologic therapies can alleviate acute and chronic pain suffering. Opioids are one type of medication used to manage pain. However, opioids can potentially create dependence and substance abuse, and the effects are not consistent in all patients. Pharmacogenomics is the study of the genome to understand the effects of drugs on individual patients based on their genetic information. Through pharmacogenomics, researchers can investigate genetic polymorphisms related to pain that maximize individual patient drug responses and minimize toxicity. This chapter discusses the pharmacogenomics of opioids to treat pain, including individual genetic differences to opioid treatments, opioid pharmacokinetics and pharmacodynamics, and the genetic polymorphisms associated with individual opioid medications.

Clinical Pharmacology of the Dietary Supplement, Kratom (Mitragyna speciosa)

Kratom (Mitragyna speciosa) consists of over 40 alkaloids with two of them, mitragynine (MG) and 7-OH-mitragynine (7-OH-MG) being the main psychoactive compounds. MG and 7-OH-MG each target opioid receptors and have been referred to as atypical opioids. They exert their pharmacologic effects on the μ, δ, and κ opioid receptors. In addition, they affect adrenergic, serotonergic, and dopaminergic pathways. Kratom has been touted as an inexpensive, legal alternative to standard opioid replacement therapy such as methadone and buprenorphine. Other uses for kratom include chronic pain, attaining a "legal high," and numerous CNS disorders including anxiety depression and post-traumatic stress disorder (PTSD). Kratom induces analgesia and mild euphoria with a lower risk of respiratory depression or adverse central nervous system effects compared to traditional opioid medications. Nonetheless, kratom has been associated with both physical and psychological dependence with some individuals experiencing classic opioid withdrawal symptoms upon abrupt cessation. Kratom use has been linked to serious adverse effects including liver toxicity, seizures, and death. These risks are often compounded by poly-substance abuse. Further, kratom may potentiate the toxicity of coadministered medications through modulation of cytochrome P450, P-glycoprotein, and uridine diphosphate glucuronosyltransferase enzymes (UGDT). In 2016 the U.S. Drug Enforcement Administration (DEA) took steps to classify kratom as a federal schedule 1 medication; however, due to public resistance, this plan was set aside. Until studies are conducted that define kratom's role in treating opioid withdrawal and/or other CNS conditions, kratom will likely remain available as a dietary supplement for the foreseeable future. This article is protected by copyright. All rights reserved.

Use of Drug Claims Data and a Medication Risk Score to Assess the Impact of CYP2D6 Drug Interactions among Opioid Users on Healthcare Costs

Cytochrome P450 2D6 (CYP2D6) activity is highly variable due to several factors, including genetic polymorphisms and drug-drug-gene interactions. Hydrocodone, oxycodone, codeine, and tramadol the most commonly prescribed CYP2D6-activated opioids for pain. However, the co-administration of CYP2D6 interacting drugs can modulate CYP2D6-medicated activation of these opioids, affecting drug analgesia, effectiveness, and safety, and can impact healthcare costs. A retrospective, observational cohort analysis was performed in a large (n = 50,843) adult population. This study used drug claims data to derive medication risk scores and matching propensity scores to estimate the effects of opioid use and drug-drug interactions (DDIs) on medical expenditures. 4088 individuals were identified as opioid users; 95% of those were prescribed CYP2D6-activated opioids. Among those, 15% were identified as being at risk for DDIs. Opioid users had a significant increase in yearly medical expenditure compared to non-opioid users ($2457 vs. $1210). In matched individuals, average healthcare expenditures were higher for opioid users with DDIs compared to those without DDIs ($7841 vs. $5625). The derived medication risk score was higher in CYP2D6 opioid users with interacting drug(s) compared to no DDI (15 vs. 12). Higher costs associated with CYP2D6 opioid use under DDI conditions suggest inadequate CYP2D6 opioid prescribing practices. Efforts to improve chronic opioid use in adults should reduce interacting drug combinations, especially among patients using CYP2D6 activated opioids.

Maternal morphine intake during pregnancy and lactation affects the circadian clock of rat pups

Early-life morphine exposure causes a variety of behavioural and physiological alterations observed later in life. In the present study, we investigated the effects of prenatal and early postnatal morphine on the maturation of the circadian clockwork in the suprachiasmatic nucleus and the liver, and the rhythm in aralkylamine N-acetyltransferase activity in the pineal gland. Our data suggest that the most affected animals were those born to control, untreated mothers and cross-fostered by morphine-exposed dams. These animals showed the highest mesor and amplitude in the rhythm of Per2, Nr1d1 but not Per1 gene expression in the suprachiasmatic nuclei (SCN) and arrhythmicity in AA-NAT activity in the pineal gland. In a similar pattern to the rhythm of Per2 expression in the SCN, they also expressed Per2 in a higher amplitude rhythm in the liver. Five of seven specific genes in the liver showed significant differences between groups in their expression. A comparison of mean relative mRNA levels suggests that this variability was caused mostly by cross-fostering, animals born to morphine-exposed dams that were cross-fostered by control mothers and vice versa differed from both groups of natural mothers raising offspring. Our data reveal that the circadian system responds to early-life morphine administration with significant changes in clock gene expression profiles both in the SCN and in the liver. The observed differences between the groups suggest that the dose, timing and accompanying stress events such as cross-fostering may play a role in the final magnitude of the physiological challenge that opioids bring to the developing circadian clock.

Searching for Scientific Explanations for the Uses of Spanish Folk Medicine: A Review on the Case of Mullein (Verbascum, Scrophulariaceae)

Verbascum species (common mullein) have been widely used in Spanish folk medicine to treat pathologies related to the musculature, skeleton, and circulatory, digestive, and respiratory systems, as well as to treat infectious diseases and organ-sense illnesses. These applications support the potential anti-inflammatory action of Verbascum phytochemicals. Based on the aforementioned facts, and following a deep bibliographic review of the chemical composition of the 10 species of Verbascum catalogued by the Spanish Inventory of Traditional Knowledge related to Biodiversity, we look for scientific evidences to correlate the traditional medical uses with the chemical components of these plants. To support these findings, in silico simulations were performed to investigate molecular interactions between Verbascum phytochemicals and cellular components. Most of common mullein traditional uses could rely on the anti-inflammatory action of phytochemicals, such as quercetin, and it could explain the employment of these plants to treat a wide range of diseases mediated by inflammatory processes such as respiratory diseases, otitis, arthrosis, and rheumatism among others.

Simultaneous LC-MS/MS quantification of oxycodone, tramadol and fentanyl and their metabolites (noroxycodone, oxymorphone, O- desmethyltramadol, N- desmethyltramadol, and norfentanyl) in human plasma and whole blood collected via venepuncture and volumetric absorptive micro sampling

INTRODUCTION

A range of opioids are commonly prescribed to manage chronic pain, but individual patient responses vary greatly, especially in older populations. One source of that variability are differences in absorption, metabolism and excretion, i.e. pharmacokinetics. Blood, plasma and serum concentrations of opioids allow that variability to be quantified and may be used to optimise opioid dosing. As an aid to that process, there is an unmet need to rapidly quantify several opioids and their metabolites in a single analytical method.

AIMS

To develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of tramadol, oxycodone, fentanyl and their major metabolites in various human matrices.

METHODS

Sample preparation involved adding three deuterated internal standards followed by protein precipitation with 100 % acetonitrile, evaporation and reconstitution. Separation of analytes via LC was achieved on a reversed phase column via binary gradient elution using 0.005 % formic acid in water and 100 % acetonitrile as mobile phases. Analytes were detected via MS/MS with multiple reaction monitoring (MRM).

RESULTS

The method was accurate with the inter-day and intra-day accuracy of quality control samples (QCs) below 15 %. It was also precise with inter-day and intra-day coefficient of variation below 15 %. The lower limit of quantification (LLOQ) was 0.2 ng/mL for all analytes except tramadol and its metabolites, where the LLOQ was 10 ng/mL. Recovery was greater than 88 % for all analytes, except for O-desmethyltramadol (81 %). Analytes were stable over four freeze-thaw cycles, for 24 h on the bench top and for 24 h post-preparation. The inter- and intra-day variability of concentrations determined in blood and plasma were within 84-124%, whereas the inter- and intra-day variability for blood samples prepared using volumetric absorptive micro-sampling (VAMS) compared to those prepared from whole blood ranged between 83-122%.

CONCLUSION

A LC-MS/MS method is described that is able to accurately and precisely quantify a number of commonly prescribed opioids and their major metabolites in plasma and whole blood, including whole blood collected using VAMS.

The Role of the Pharmacist in the Care of Patients with Chronic Pain

Pharmacists across the healthcare continuum are well positioned to collaborate with patients to effectively manage their chronic pain. Evidence supports positive outcomes when pharmacists undertake these roles; however, there are barriers preventing uptake across the profession. This paper aims to expand awareness of the breadth of these roles, including pharmaceutical care provision, interprofessional collaboration, pain and medication education, support for patients in self-management and acceptance of responsibility to be culturally responsive and decrease stigma. Pharmacists are accessible healthcare professionals and can improve the care of patients with chronic pain.

Tolerance to Opioid-Induced Respiratory Depression in Chronic High-Dose Opioid Users: A Model-Based Comparison With Opioid-Naïve Individuals

Chronic opioid consumption is associated with addiction, physical dependence, and tolerance. Tolerance results in dose escalation to maintain the desired opioid effect. Intake of high-dose or potent opioids may cause life-threatening respiratory depression, an effect that may be reduced by tolerance. We performed a pharmacokinetic-pharmacodynamic analysis of the respiratory effects of fentanyl in chronic opioid users and opioid-naïve subjects to quantify tolerance to respiratory depression. Fourteen opioid-naïve individuals and eight chronic opioid users received escalating doses of intravenous fentanyl (opioid-naïve subjects: 75-350 µg/70 kg; chronic users: 250-700 µg/70 kg). Isohypercapnic ventilation was measured and the fentanyl plasma concentration-ventilation data were analyzed using nonlinear mixed-effects modeling. Apneic events occurred in opioid-naïve subjects after a cumulative fentanyl dose (per 70 kg) of 225 (n = 3) and 475 µg (n = 6), and in 7 chronic opioid users after a cumulative dose of 600 (n = 2), 1,100 (n = 2), and 1,800 µg (n = 3). The time course of fentanyl's respiratory depressant effect was characterized using a biophase equilibration model in combination with an inhibitory maximum effect (Emax ) model. Differences in tolerance between populations were successfully modeled. The effect-site concentration causing 50% ventilatory depression, was 0.42 ± 0.07 ng/mL in opioid-naïve subjects and 1.82 ± 0.39 ng/mL in chronic opioid users, indicative of a 4.3-fold sensitivity difference. Despite higher tolerance to fentanyl-induced respiratory depression, apnea still occurred in the opioid-tolerant population indicative of the potential danger of high-dose opioids in causing life-threatening respiratory depression in all individuals, opioid-naïve and opioid-tolerant.

Opioid prescribing and risk of drug-opioid interactions in older discharged patients with polypharmacy in Australia

Background Opioids are commonly prescribed to managing chronic pain in older persons. However, these patients are often at risk of drug-opioid interactions due to polypharmacy. Objectives To identify the prevalence of opioid prescribing and drug-opioid interactions in poly-medicated older patients and factors associated with opioid prescribing. Setting Patients were included if they were admitted to the Royal Adelaide Hospital between September 2015 and August 2016, aged ≥ 75 years and took ≥ 5 medications at discharge. Methods After ethics approval, data of were retrospectively collected from case notes. The Charlson Comorbidity Index and Drug Burden Index were determined and opioids were classified as strong or weak. The association between opioid use and concurrent medications was computed using logistic regression and the results presented as odds ratios (OR) and 95% confidence intervals (95% CI), adjusted for age, sex, Charlson Comorbidity Index, number of prescribed medications and modified-Drug Burden Index. Main outcome measure Association between concurrent medications and opioid prescribing. Results 15,000 geriatric admissions were identified, of which 1192 were included. A total of 283 (23.7%) patients were prescribed opioids, with oxycodone accounting for 56% of these prescriptions. Opioid users were prescribed more medications (11.2 vs. 9.0, P < 0.001) and had higher Drug Burden Index (1.2 vs. 0.14, P < 0.001) compared to non-users. Opioid use was associated with concurrent prescription of antiepileptics (OR = 1.7, 95% CI 1.1-2.6), and negatively associated with Charlson Comorbidity Index (OR = 0.9, 95% CI 0.8-0.98) and concurrent use of antipsychotics (OR = 0.5, 95% CI 0.3-0.9) and beta blocking agents (OR = 0.4, 95% CI 0.3-0.6). Conclusions Strong opioids were prescribed more often than weak opioids and opioid users presented with characteristics and concurrent medications which increased the risk of opioid related adverse drug effects.

Glutathione and Glutathione-Like Sequences of Opioid and Aminergic Receptors Bind Ascorbic Acid, Adrenergic and Opioid Drugs Mediating Antioxidant Function: Relevance for Anesthesia and Abuse

Opioids and their antagonists alter vitamin C metabolism. Morphine binds to glutathione (l-γ-glutamyl-l-cysteinyl-glycine), an intracellular ascorbic acid recycling molecule with a wide range of additional activities. The morphine metabolite morphinone reacts with glutathione to form a covalent adduct that is then excreted in urine. Morphine also binds to adrenergic and histaminergic receptors in their extracellular loop regions, enhancing aminergic agonist activity. The first and second extracellular loops of adrenergic and histaminergic receptors are, like glutathione, characterized by the presence of cysteines and/or methionines, and recycle ascorbic acid with similar efficiency. Conversely, adrenergic drugs bind to extracellular loops of opioid receptors, enhancing their activity. These observations suggest functional interactions among opioids and amines, their receptors, and glutathione. We therefore explored the relative binding affinities of ascorbic acid, dehydroascorbic acid, opioid and adrenergic compounds, as well as various control compounds, to glutathione and glutathione-like peptides derived from the extracellular loop regions of the human beta 2-adrenergic, dopamine D1, histamine H1, and mu opioid receptors, as well as controls. Some cysteine-containing peptides derived from these receptors do bind ascorbic acid and/or dehydroascorbic acid and the same peptides generally bind opioid compounds. Glutathione binds not only morphine but also naloxone, methadone, and methionine enkephalin. Some adrenergic drugs also bind to glutathione and glutathione-like receptor regions. These sets of interactions provide a novel basis for understanding some ways that adrenergic, opioid and antioxidant systems interact during anesthesia and drug abuse and may have utility for understanding drug interactions.

Role of Opioid-Involved Drug Interactions in Chronic Pain Management

The use of opioids for chronic pain management is extraordinarily common despite substantial evidence of only modest benefits, when compared with nonopioid analgesics. Opioid use is also associated with serious risks, including overdose and death. A growing body of evidence suggests that opioids are involved in significant drug interactions that often go unrecognized in clinical practice. Understanding opioid-involved drug interactions is of great practical importance for all health care professionals caring for patients with chronic pain. In this article, we describe the mechanisms of opioid-involved drug interactions and their potential consequences, which have major public health implications. Additionally, this article provides practical strategies to aid health care professionals in avoiding and mitigating opioid-involved drug interactions in order to obtain a favorable balance in the risk-benefit ratio associated with opioid use. These strategies include using osteopathic principles for chronic pain management, separating the times of administration of the opioid(s) from the nonopioid(s) involved in the interaction, changing the opioid(s) adversely affected by the interaction, changing the nonopioid(s) causing the interaction, and partnering with pharmacists in clinical practice.

Opioids: Pharmacology, Physiology, and Clinical Implications in Pain Medicine

Opioid receptors and opioid agonists are widespread throughout nature. Endogenous opioids mediate complex functions in animals and in humans. The opioid system in humans plays a central role in pain control and is a key mediator of hedonic homeostasis, mood, and well-being. This system also regulates responses to stress and several peripheral physiologic functions, including respiratory, gastrointestinal, endocrine, and immune systems. This article provides an overview of the basic physiology of opioids, reviews opioid pharmacology, and attempts to address several issues of current importance in the management of patients with established long-term opioid therapy.

Identification of Cytochrome P450 Polymorphisms in Burn Patients and Impact on Fentanyl Pharmacokinetics: A Pilot Study

Pain management is critical for burn care. Unfortunately, interindividual variation in pharmacokinetics (PK) due to burn hypermetabolism and genetic polymorphisms can lead to treatment failures in this at-risk population. Analgesics may be affected by genetic polymorphisms affecting cytochrome P450 (CYP) drug metabolizing enzymes. Fentanyl is a common opiate primarily metabolized by CYP3A4 subtypes. Recent studies demonstrate CYP2D6 variants, affecting fentanyl PK. Functional CYP polymorphisms can significantly alter opiate levels resulting in inadequate analgesia or life-threatening toxicity. The goal of our study was to evaluate fentanyl PK and assess associations with CYP polymorphisms. We obtained samples from the previously banked blood of 13 patients (eight males and five females) with >20% TBSA burns. Mean (SD) patient age was 41.7 (14.5) years, and mean burn size was 25.8 (15.3) %TBSA. Plasma fentanyl was quantified, and CYP genotyping was performed. Pharmacokinetic analysis was performed using Monolix software (Lixsoft, France) with a two-compartment population model best-representing fentanyl profiles. Three CYP slow-metabolizing genotypes were identified, which included CYP2D6*9, CYP2D6*29, and CYP3A4*1B. All three patients with variant polymorphisms had increased serum fentanyl concentrations due to impaired clearance. This pilot study supports the need for further research in this topic, and CYP genotyping of individual patients prior to receiving opiate analgesics to inform precision-guided decisions, improve therapeutic efficacy, and, most importantly, increase patient well-being and safety.

Direct-acting antiviral interactions with opioids, alcohol or illicit drugs of abuse in HCV-infected patients

The hepatitis C virus (HCV) prevalence is extremely high in patients who consume and inject illicit drugs. Concerns about poor adherence and fear of interaction with drugs of abuse could constitute further disincentive for treatment initiation in these patients. We discussed the pharmacokinetics (PKs) and pharmacodynamics (PD) of currently prescribed direct antiviral agents (NSA5 inhibitors: daclatasvir, elbasvir, ledipasvir, pibrentasvir, velpatasvir; NS5B inhibitor: sofosbuvir; NS3/4A protease inhibitors: glecaprevir, grazoprevir, voxilaprevir) and most common substances of abuse (opioids: buprenorphine, fentanyl, heroin, methadone, morphine, oxycodone; stimulants: amphetamines, cathinones, cocaine; cannabinoids; ethanol). Overall, most direct-acting antivirals (DAAs) are substrates and inhibitors of the transmembrane transporter P-glycoprotein (P-gp), and several of them are metabolized by cytochrome P450 enzymes. Clinically relevant interactions are associated with P-gp and CYP3A modulators. Most substances of abuse are eliminated by Phase I and Phase II metabolizing enzymes, but none of them are either major inhibitors or inducers. PK studies did not show any relevant interactions between DAA and methadone or buprenorphine. Based on pharmacological considerations, neither efficacy loss nor adverse drug event associated with detrimental interaction are expected with opioids, stimulants, cannabinoids and ethanol. In summary, our literature review shows that the interaction potential of DAA with most opioids and illicit drugs is limited and should not be a hurdle to the initiate DAA.

Adapting the Social-Ecological Framework for Chronic Pain Management and Successful Opioid Tapering

Context

In 2015, Solano County's Medi-Cal insurer implemented a new policy to taper patients using high-dose opioids (≥120-mg morphine equivalent dose) to a safer level to follow best practices to address the opioid epidemic.

Objective

To evaluate the effect of the 2015 Solano County Medi-Cal prescribing policy, gain insight into the patient experience of undergoing opioid tapering, and generate hypotheses for further study.

Methods

Using a case series approach, researchers completed medical record reviews of affiliated clinical records, Solano County Vital Statistics, and California's prescription monitoring program in 2018. After exclusions, eligible patients were asked to participate in a comprehensive qualitative interview.

Results

Medical record reviews of 38 patients found the majority were not using opioids using them at a morphine equivalent dose of 90 mg or less. The reviews also found that mental illness and obesity prevalence were higher than Solano county baseline levels. Furthermore, naloxone was not prescribed to any of the 38 patients. Researchers reached 15 of the 38 patients by phone, and ultimately 6 completed the interview process. Themes and emergent concepts from interviews identified a lack of empathetic connection with health care professionals, poor understanding of overdose risks, persistent pain, and confirmed naloxone underuse.

Conclusion

Safer prescribing policies may take multiple years to fully implement and need to be employed across the jurisdiction to minimize doctor-shopping and adverse effects on patients with chronic pain. Approaching pain management through the social-ecological model can address potential root causes of addiction and establish a framework for doctors to provide compassionate care, community leadership, and advocacy for these patients.

A Retrospective Analysis of Selected Opioids in Hair of Workplace Drug Testing Subjects

Opioids, both naturally occurring and semisynthetic, are effective pain management medications, but also possess the potential for abuse. Analyses of over 37,000 head and body hair samples containing codeine, morphine, hydrocodone, hydromorphone, oxycodone or oxymorphone provide a view of use habits of workplace-testing subjects that cannot be obtained from fluid matrices results. Testing was performed using FDA cleared immunoassays using either 2 ng morphine or oxycodone per 10 mg hair as calibrators. Non-negative screening samples were washed with an extended aqueous wash procedure followed by LC-MS-MS confirmation at a cutoff concentration of 2 ng opioid per 10 mg hair. The LC-MS-MS method measured codeine, morphine, 6-acetylmorphine, hydrocodone, hydromorphone, oxycodone and oxymorphone with an administratively established LOQ of 0.50 ng opioid per 10 mg hair. The linear range was 0.50-100 ng morphine per 10 mg hair, and 0.50-150 ng opioid per 10 mg hair for all other measured analytes. For all analytes, within run precision was ≤5.4%, and between-run precision was ≤6.4%. Analysis of samples containing metabolites found that, among codeine positive samples, 97% contained less than 10% morphine metabolite and 88% less than 20% hydrocodone metabolite, among hydrocodone positive samples, 97% contained less than 10% hydromorphone metabolite and 95% of oxycodone positive samples contained less than 10% oxymorphone metabolite. Our analysis of opioid-positive samples may provide guidelines for interpretation of hair opioid levels typically observed in workplace testing.

Identification potential inhibitors against the Streptococcus quorum-sensing signal pathway

Streptococcal infections are common in human and antibiotics are frequently prescribed in clinical practice. However, infections caused by drug-resistant strains are particularly difficult to treat using common antibiotics. Hence, there is an urgent need for new antibiotics. Quorum sensing is a regulatory mechanism involving cell communication that is thought to play an important role in various bacterial infections, including those caused by Streptococcus. The ATP-binding cassette transporter ComA of Streptococcus is essential for quorum-sensing signal production. The inhibition of the ComA peptidase domain (ComA PEP) suppresses the quorum-sensing pathway and resulting changes in phenotype and/or behavior. Using virtual screening and molecular dynamics simulations, two promising candidate compounds, ZINC32918029 and ZINC6751571, were found. These compounds had similar binding modes and interactions to the experimentally determined reference inhibitor 6CH. However, a significantly stronger negative binding energy was achieved (-113.501 ± 15.312 KJ/mol and -103.153 ± 11.912 KJ/mol for ZINC32918029 and ZINC6751571, respectively). Molecular dynamics simulations also revealed that ZINC32918029 and ZINC6751571 had a strong affinity for ComA PEP. These results indicate that ZINC32918029 and ZINC6751571 are promising candidate inhibitors of the Streptococcus quorum-sensing pathway.Communicated by Ramaswamy H. Sarma.

Biotransformation, Using Recombinant CYP450-Expressing Baker's Yeast Cells, Identifies a Novel CYP2D6.10A122V Variant Which Is a Superior Metabolizer of Codeine to Morphine Than the Wild-Type Enzyme

CYP2D6, a cytochrome P450 (CYP) enzyme, metabolizes codeine to morphine. Within the human body, 0-15% of codeine undergoes O-demethylation by CYP2D6 to form morphine, a far stronger analgesic than codeine. Genetic polymorphisms in wild-type CYP2D6 (CYP2D6-wt) are known to cause poor-to-extensive metabolism of codeine and other CYP2D6 substrates. We have established a platform technology that allows stable expression of human CYP genes from chromosomal loci of baker's yeast cells. Four CYP2D6 alleles, (i) chemically synthesized CYP2D6.1, (ii) chemically synthesized CYP2D6-wt, (iii) chemically synthesized CYP2D6.10, and (iv) a novel CYP2D6.10 variant CYP2D6-C (i.e., CYP2D6.10^A122V) isolated from a liver cDNA library, were cloned for chromosomal integration in yeast cells. When expressed in yeast, CYP2D6.10 enzyme shows weak activity compared with CYP2D6-wt and CYP2D6.1 which have moderate activity, as reported earlier. Surprisingly, however, the CYP2D6-C enzyme is far more active than CYP2D6.10. More surprisingly, although CYP2D6.10 is a known low metabolizer of codeine, yeast cells expressing CYP2D6-C transform >70% of codeine to morphine, which is more than twice that of cells expressing the extensive metabolizers, CYP2D6.1, and CYP2D6-wt. The latter two enzymes predominantly catalyze formation of codeine's N-demethylation product, norcodeine, with >55% yield. Molecular modeling studies explain the specificity of CYP2D6-C for O-demethylation, validating observed experimental results. The yeast-based CYP2D6 expression systems, described here, could find generic use in CYP2D6-mediated drug metabolism and also in high-yield chemical reactions that allow the formation of regio-specific dealkylation products.

Beneficial effects of Bacopa monnieri extract on opioid induced toxicity

The present study examined the hepatotoxicity and nephrotoxicity of morphine and illicit street heroin and their amelioration by a standardized methanolic extract of Bacopa monnieri (L.) (mBME) in rats. Morphine or street heroin was administered at a dose of 20 mg/kg for 14 and 21 days. mBME (40 mg/kg) or ascorbic acid (50 mg/kg) was administered two hours before morphine or street heroin. High performance liquid chromatography (HPLC) was used for the standardization of bacoside-A major components in mBME. The antioxidant potential of mBME was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. Administration of morphine and street heroin resulted in marked elevation of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and creatinine. Histopathological changes induced by morphine and street heroin after 14 days were of reversible nature while treatment for 21 days was associated with irreversible changes. Pretreatment with mBME or ascorbic acid restored the elevation of serum ALT, AST and creatinine and protected liver and kidneys from the toxicological influence of morphine and street heroin. HPLC analysis showed that mBME contained bacoside-A major components i.e. bacoside-A₃ (37.5 μg/mg), bacopaside-II (4.62 μg/mg) and bacopasaponin-C (1.91 μg/mg). The EC₅₀ for the DPPH free radical scavenging assay revealed that mBME possessed strong antioxidant potential. These results concluded that as compared to morphine, street heroin was associated with severe biochemical and histopathological changes in the liver and kidneys. Bacopa monnieri having strong antioxidant potential may provide a beneficial herbal remedy for the efficient management of opioid related hepatotoxicity and nephrotoxicity.

Opioid Medication Practices Observed in Chronic Pain Patients Presenting for All-Causes to Emergency Departments: Prevalence and Impact on Health Care Outcomes

BACKGROUND

Chronic pain is a significant health problem that affects an estimated 100 million American adults (aged ≥ 18 years). Chronic pain affects more individuals than heart disease, stroke, diabetes, and cancer combined. Chronic pain sufferers cost up to $635 billion annually in medical treatment and lost productivity. Opioids are commonly used to treat chronic pain, but their metabolic interactions with concurrently prescribed medications for concomitant disease burdens can affect potency and efficacy of pain therapy. Additionally, misuse of short-acting opioids (SAOs) for chronic pain versus breakthrough pain can create gaps in pain relief. These potentially suboptimal prescribing practices may contribute to the high economic impact associated with chronic pain. 

OBJECTIVE

To examine the prevalence of suboptimal opioid therapy and the associated health care costs resulting from these prescribing practices in real-world patients presenting for all-causes to the emergency department (ED). 

METHODS

This retrospective observational database cohort analysis used the linked Premier-Optum database and included patients with ED visits from 2006 to 2010 having ≥ 60 days supply of opioids in the 75 days prior to the visit. Suboptimal prescribing practices were identified as patients with (a) drug-drug exposures (DDEs), defined as cytochrome P-450 (CYP-450)-metabolized opioids prescribed concurrently with CYP-450 inhibitors or inducers and/or (b) monotherapy with SAOs. Comorbid conditions and principal diagnoses were documented. Readmission rates to the ED and hospital within 72 hours as well as ≤ 30, ≤ 45, ≤ 60, and ≤ 90 days were computed. Total costs for health care were calculated, and reimbursement rates were normalized using 2011 Medicare severity diagnosis-related group (MS-DRG) and CPT-4 information. Nonparametric bootstrapping to adjust for patient comorbidities was applied to cost data.

RESULTS

Of the 9,214 patients identified with chronic pain, potentially suboptimal medication practices prior to the index ED visit were found for 8,539 (92.6%) patients. These appeared to be corrected in 345 (4.0%) patients before leaving the ED. Of 675 (7.3%) patients without prior DDE or exclusive use of SAOs, 345 (51.1%) patients were discharged with one of these. Of the 8,352 patients who left the ED with DDE or exclusive use of SAOs, 1,525 (18.3%) left with a DDE without exclusive SAO use; 4,812 (57.6%) left with both DDE and exclusive SAO use; and 2,015 (24.1%) left with only exclusive SAO use. Only 862 (9.3%) patients from the entire cohort left the ED without DDE or exclusive SAO use. Patients identified with suboptimal opioid use were aged 50 ± 13.5 years and were predominantly female (64.0%). Hypertension (44.0%), fluid and electrolyte disorders (32.7%), chronic pulmonary disease (22.8%), depression (19.6%), diabetes without chronic complications (16.2%), and drug abuse (15.6%) were the most prevalent comorbid conditions identified. The most prevalent principal diagnoses involved symptoms and signs of ill-defined conditions (36.5%), injury and poisoning (18.2%), and diseases of the musculoskeletal system (13.2%). The majority of revisits to the ED and hospital admissions occurred within 72 hours (73.6%) of the index visit and within 30 days (70%), respectively. When adjusted total costs were compared for all patients whose opioid use included DDE versus those without, a significantly greater cost (P  less than  0.05) was observed at every time period except ≤ 72 hours. Respective mean increases in costs were $581, $689, $773, and $1,275 at 30, 45, 60, and 90 days. Exclusive SAO use with or without DDE resulted in a significant increase (P  less than  0.05) in mean costs at all times: $214 at 72 hours; $836 at 30 days; $1,023 at 45 days; $1,022 at 60 days; and $1,536 at 90 days. 

CONCLUSIONS

This study identified potentially suboptimal opioid prescribing practices in a real-world population presenting for all-causes to the ED. The observed rate of ED revisits and inpatient admissions in these patients was associated with increased health care costs. These findings suggest that the ED has the future potential to serve as an ideal setting to identify and correct such practices, thereby improving patient care and reducing resource use and beneficiary costs.

Parent and Metabolite Opioid Drug Concentrations in Unintentional Deaths Involving Opioid and Benzodiazepine Combinations

Effects of benzodiazepines on postmortem opioid parent and parent/metabolite blood concentration ratios were determined for fentanyl-, hydrocodone-, methadone-, or oxycodone-related accidental deaths. These opioids are partially metabolized by the CYP3A4 enzyme system, which is also affected by diazepam and alprazolam. Opioid/metabolite combinations examined were as follows: fentanyl/norfentanyl, hydrocodone/dihydrocodeine, methadone/EDDP, and oxycodone/oxymorphone. Parent opioid concentrations were analyzed for 877 deaths. Parent/metabolite concentration ratios were analyzed for 349 deaths, excluding cases with co-intoxicants present known to interfere with opioid elimination. Alprazolam in combination with diazepam significantly decreased median hydrocodone concentrations by 48% (p = 0.01) compared to hydrocodone alone. The methadone parent/metabolite concentration ratio was reduced by 35% in the presence of diazepam compared to methadone alone (p = 0.03). Benzodiazepines did not statistically significantly affect fentanyl or oxycodone concentrations. Possible factors affecting opioid concentrations and possible toxicity development, including any differential effects on specific opioids, should continue to be explored.

Relationship between plasma concentrations of the l-enantiomer of methadone and response to methadone maintenance treatment

This study evaluated the relationship between the plasma concentration of l-methadone and response to methadone in real-world patients, in order to identify a minimum plasma concentration above which methadone treatment is effective. Ninety-four patients with opioid dependence under maintenance methadone treatment were consecutively recruited. Response was defined as negative urine analyses in the three weeks prior to the blood sampling. The percentage of participants with a plasma l-methadone concentration between 100 and 250 ng/ml was 54.2% among those with a methadone dosage ≥60 mg/day. Plasma l-methadone concentrations were significantly higher in patients with negative urine analyses compared with those with positive urine analyses (median 93 vs. 77 ng/ml, Mann-Whitney test, P<0.05). Above plasma l-methadone concentrations of 200 ng/ml no heroin use was reported and urine analyses were negative. Moreover, above concentrations of 250 ng/ml craving was absent. Examination of demographic correlates of treatment outcome indicated that older age, a stable job and being married were protective against the use of heroin. Mean plasma l-methadone concentration was significantly lower in patients who used cannabis compared with those who did not use cannabis, after adjusting for methadone dosage. In conclusion our results identify specific cut-offs for plasma l-methadone concentrations about which therapeutic response is observed and provide new evidence that therapeutic response is associated with patient׳s demographic characteristics. This underscores the need to monitor plasma methadone concentrations as part of Drug Addiction Services routine practice, in order to provide an objective framework for changing the methadone dosage.

Codeine-induced hyperalgesia and allodynia: investigating the role of glial activation

Chronic morphine therapy has been associated with paradoxically increased pain. Codeine is a widely used opioid, which is metabolized to morphine to elicit analgesia. Prolonged morphine exposure exacerbates pain by activating the innate immune toll-like receptor-4 (TLR4) in the central nervous system. In silico docking simulations indicate codeine also docks to MD2, an accessory protein for TLR4, suggesting potential to induce TLR4-dependent pain facilitation. We hypothesized codeine would cause TLR4-dependent hyperalgesia/allodynia that is disparate from its opioid receptor-dependent analgesic rank potency. Hyperalgesia and allodynia were assessed using hotplate and von Frey tests at days 0, 3 and 5 in mice receiving intraperitoneal equimolar codeine (21 mg kg(-1)), morphine (20 mg kg(-1)) or saline, twice daily. This experiment was repeated in animals with prior partial nerve injury and in TLR4 null mutant mice. Interventions with interleukin-1 receptor antagonist (IL-1RA) and glial-attenuating drug ibudilast were assessed. Analyses of glial activation markers (glial fibrillary acid protein and CD11b) in neuronal tissue were conducted at the completion of behavioural testing. Despite providing less acute analgesia (P=0.006), codeine induced similar hotplate hyperalgesia to equimolar morphine vs saline (-9.5 s, P<0.01 and -7.3 s, P<0.01, respectively), suggesting codeine does not rely upon conversion to morphine to increase pain sensitivity. This highlights the potential non-opioid receptor-dependent nature of codeine-enhanced pain sensitivity-although the involvement of other codeine metabolites cannot be ruled out. IL-1RA reversed codeine-induced hyperalgesia (P<0.001) and allodynia (P<0.001), and TLR4 knock-out protected against codeine-induced changes in pain sensitivity. Glial attenuation with ibudilast reversed codeine-induced allodynia (P<0.001), and thus could be investigated further as potential treatment for codeine-induced pain enhancement.

Economic implications of potential drug-drug interactions in chronic pain patients

Chronic pain patients may be subject to polypharmacy because of long-term pharmacological pain treatment and additional comorbidities. Many chronic pain patients expose themselves to potential drug-drug interactions (DDIs) and these interactions can have unintended and severe consequences. Prevalence and costs associated with DDIs are inconsistent and has led to an inadequate level of awareness among the medical community; therefore, it has become necessary to re-evaluate the rates of DDIs in chronic pain patients. Utilizing medical and prescription claims databases, five studies were conducted to assess the health care utilization of and associated financial payments for patients >18 years with chronic noncancer pain. The studies evaluated drug-drug exposures with the potential to cause DDIs specifically occurring through the CYP450 enzyme system. The studies reported that drug-drug exposures are prevalent, costly and can occur in any age group and that physicians should consider ways to limit their patients' exposure to potential DDIs.

Cytochrome P450 2D6 based electrochemical sensor for the determination of codeine

Considering the enzymatic activity of the cytochrome P450 2D6 on substrates such as codeine, the current paper includes the development of an enzymatic biosensor for detection of this drug. Home-made screen-printed electrodes were used as electrochemical transducers of the biosensor, in which the enzyme was covalently attached to the carbon surface of the working electrode, this type of modification being the most suitable for the immobilization of the biological element. Chronoamperometric measurements were carried out under optimum conditions of pH and working potential, pH 7 and +200 mV vs. screen-printed Ag/AgCl electrode, giving a reduction signal related to the concentration of codeine in solution. Consecutive additions of a solution of codeine were performed to obtain calibration curves in order to validate the electrochemical method in terms of precision and calculate its capability of detection. These biosensors were used for the determination of codeine in urine and commercial pharmaceutical samples.

Sulfation of opioid drugs by human cytosolic sulfotransferases: metabolic labeling study and enzymatic analysis

The current study was designed to examine the sulfation of eight opioid drugs, morphine, hydromorphone, oxymorphone, butorphanol, nalbuphine, levorphanol, nalorphine, and naltrexone, in HepG2 human hepatoma cells and human organ samples (lung, liver, kidney, and small intestine) and to identify the human SULT(s) responsible for their sulfation. Analysis of the spent media of HepG2 cells, metabolically labeled with [35S]sulfate in the presence of each of the eight opioid drugs, showed the generation and release of corresponding [35S]sulfated derivatives. Five of the eight opioid drugs, hydromorphone, oxymorphone, butorphanol, nalorphine, and naltrexone, appeared to be more strongly sulfated in HepG2 cells than were the other three, morphine, nalbuphine, and levorphanol. Differential sulfating activities toward the opioid drugs were detected in cytosol or S9 fractions of human lung, liver, small intestine, and kidney, with the highest activities being found for the liver sample. A systematic analysis using eleven known human SULTs and kinetic experiment revealed SULT1A1 as the major responsible SULTs for the sulfation of oxymorphone, nalbuphine, nalorphine, and naltrexone, SULT1A3 for the sulfation of morphine and hydromorphone, and SULT2A1 for the sulfation of butorphanol and levorphanol. Collectively, the results obtained imply that sulfation may play a significant role in the metabolism of the tested opioid drugs in vivo.

A simple liquid chromatography-tandem mass spectrometry method for determination of plasma fentanyl concentration in rats and patients with cancer pain

A fentanyl patch is widely used for the treatment of cancer pain. Its few adverse effects include constipation and drowsiness. The absorption volume of transdermally applied fentanyl may differ according to its site of application and variability in patch adhesion. Since fentanyl is predominantly metabolized by the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 in the liver, its concentration may vary in cases of physiologically reduced CYP3A4 activity in the liver (liver disease and aging) or on co-administration of drugs. The clinical significance of measuring plasma concentration of fentanyl is high, but conventional methods require complicated processes such as solid-phase extraction and liquid-liquid extraction before the sample is injected into an HPLC system. In this study, a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for determining plasma fentanyl concentrations by deproteinization with acetonitrile. A recovery test was conducted using an absolute calibration curve to confirm the method's linearity and inter- and intra-day reproducibility. The required plasma volume for detection was reduced from 1 mL in the conventional method to 20 µL in the present study, and a good calibration curve was obtained in the concentration range from 0.05 to 5 ng/mL. These findings suggest that the method for sample preparation and quantification developed in this study are appropriate for measuring fentanyl concentration in human plasma in clinical settings.

Opioid therapies and cytochrome p450 interactions

Adverse drug reactions are common and associated with substantial economic and human costs. Particularly among older adult populations, preventable adverse drug reactions are often caused by drug-drug interactions. All analgesics have side effect profiles and many have known drug-drug interactions. Opioids are recognized as a necessary option for managing moderate-to-severe pain, yet many opioid side effects can be enhanced by metabolic interactions within the liver, involving other drugs, diseases, or genetics.

The association of CYP2D6 genotype and postoperative nausea and vomiting in orthopedic trauma patients

The CYP2D6 gene encodes for an enzyme that is involved in the metabolism of more than 25% of all medications, including many opioids and antiemetics. It may contribute to the risk of postoperative nausea and vomiting (PONV), a common surgical complication. However, little research has been conducted in this area. The purpose of this study was to explore the association of CYP2D6 genotypes with PONV in adult surgical trauma patients. Data from 112 patients (28% female) with single extremity fractures, aged 18-70 years, were analyzed. PONV was defined as present if patients reported nausea, were observed vomiting, or received medication for PONV. Saliva samples collected for DNA extraction and Taqman(®) allele discrimination and quantitative real time polymerase chain reaction (qRT-PCR) were used to collect genotype data that were then used to assign CYP2D6 phenotype classification. The incidence of PONV was 38% in the postanesthesia care unit and increased to 50% when assessed at 48 hr. CYP2D6 classification results were 7 (6%) poor metabolizers, 34 (30%) intermediate metabolizers, and 71 (63%) extensive metabolizers. No ultrarapid metabolizers were identified. Patients who were classified as poor metabolizers had less PONV and higher pain scores. Gender and history of PONV, but not smoking, were also significant risk factors. Findings suggest variability in CYP2D6 impacts susceptibility to PONV.

Mechanistic and functional differentiation of tapentadol and tramadol

INTRODUCTION

Many opioid analgesics share common structural elements; however, minor differences in structure can result in major differences in pharmacological activity, pharmacokinetic profile, and clinical efficacy and tolerability.

AREAS COVERED

This review compares and contrasts the chemistry, pharmacodynamics, pharmacokinetics, and CNS 'functional activity' of tapentadol and tramadol, responsible for their individual clinical utilities.

EXPERT OPINION

The distinct properties of tapentadol and tramadol generate different CNS functional activities, making each drug the prototype of different classes of opioid/nonopioid analgesics. Tramadol's analgesia derives from relatively weak µ-opioid receptor (MOR) agonism, plus norepinephrine and serotonin reuptake inhibition, provided collectively by the enantiomers of the parent drug and a metabolite that is a stronger MOR agonist, but has lower CNS penetration. Tapentadol's MOR agonist activity is several-fold greater than tramadol's, with prominent norepinephrine reuptake inhibition and minimal serotonin effect. Accordingly, tramadol is well-suited for pain conditions for which a strong opioid component is not needed-and it has the benefit of a low abuse potential; whereas tapentadol, a schedule-II controlled substance, is well-suited for pain conditions requiring a strong opioid component-and it has the benefit of greater gastrointestinal tolerability compared to classical strong opioids. Both drugs offer distinct and complementary clinical options.

CYP2D6 polymorphisms and codeine analgesia in postpartum pain management: a pilot study

BACKGROUND

Codeine, a common opiate prescribed for pain postcesarean section (c-section), is biotransformed by the highly polymorphic Cytochrome P450 enzyme 2D6 (CYP2D6). Ultrarapid metabolizers (UMs), individuals with multiple active copies of CYP2D6, can biotranform up to 50% more codeine into morphine than normal individuals can. In contrast, poor metabolizers (PMs), individuals who have no active CYP2D6 genes, convert almost no codeine into morphine and as a result may take multiple doses of codeine without attaining analgesia.

OBJECTIVE

The aim was to study the relationship between CYP2D6 genotype and codeine analgesia among women recovering from c-section.

METHODS

Forty-five mothers prescribed codeine provided a blood sample for CYP2D6 genotyping and recorded their pain level 4 times a day for 3 days immediately after a c-section. Codeine was used on an as-needed basis; doses and times were recorded. The relationship between CYP2D6 genotype, pain scores, need for codeine, and adverse events was studied. Theoretical morphine dose, based on CYP2D6 genotype, was estimated.

RESULTS

Women at the genotypic extremes reported codeine effects consistent with their genotype: the 2 PMs of codeine reported no analgesia as a result of taking codeine, whereas 2 of the 3 UMs reported immediate pain relief from codeine but stopped taking it due to dizziness and constipation. Much larger numbers are needed to study similar correlations among extensive and intermediate metabolizers.

CONCLUSIONS

In this pilot study, the extreme CYP2D6 genotypes (PMs and UMs) seemed to predict pain response and adverse events. Larger sample sizes are needed to correlate the range of genotypes with pain response.

Economic impact of potential CYP450 pharmacokinetic drug-drug interactions among chronic low back pain patients taking opioids

Chronic low back pain (cLBP) patients who take at least 1 CYP450-metabolized opioid analgesic agent concurrent with at least 1 other CYP450-metabolized medication experience a drug-drug exposure (DDE), which puts them at risk for a pharmacokinetic drug-drug interaction (PK DDI). This study compared utilization of healthcare resources and associated payments in cLBP patients with and without incident DDEs with the potential to cause PK DDIs. A retrospective database analysis examined the associated clinical events, healthcare utilization (measured in terms of claims for office visits, outpatient visits, emergency department visits, and hospitalization), and cost to the health plan, as defined as the sum of health plan payments for resources used. Patients were grouped into 2 cohorts by age (those under 65 and those 65 years and over). In the 6 months after exposure, total healthcare payments were significantly higher for DDE patients than those without DDEs (no-DDE), in both in the younger ($7,086, SD = $8,370) and $6,353, SD = $8,352, respectively, P < 0.001) and the older cohorts ($7,806 vs. $7,043, respectively, P = 0.013). Younger and older patients with DDE had significantly higher prescription payments than those without DDE ($2,041, SD = $2,706 vs. $1,565, SD = $2,349, respectively, P < 0.001 for younger and $2,482, SD = $2,481 vs. $2,286, SD = $2,521, respectively, P = 0.044 for older patients). Both older and younger patients with DDE had significantly more claims for office visits and higher associated payments than similar patients without DDE. Patients in the study who experienced DDEs that placed them at risk for PK DDIs had significantly greater utilization rates of healthcare resources and higher associated payments in the 6-month observation period following exposure.

Economic impact of potential drug-drug interactions in opioid analgesics

OBJECTIVE

Patients managing chronic non-cancer pain with cytochrome P450 (CYP450)-metabolized opioid analgesics who concurrently take another CYP450-metabolized medication experience a drug-drug exposure (DDE), which puts them at risk for a pharmacokinetic drug-drug interaction (PK DDI). This study examined the economic impact of incident DDEs with the potential to cause PK DDIs compared to similar patients without such exposure.

STUDY DESIGN

This retrospective analysis used paid claims from a large, commercially insured population during January 1, 2004 through December 31, 2008.

METHODS

Propensity matching was used to control for baseline differences in comparisons between 85,043 exposed and 85,043 non-exposed patients.

RESULTS

Comparisons yielded mean total costs 6 months after the DDEs that were significantly higher in subjects with DDE versus matched subjects without DDE [$8165 (SD $11,357) vs. $7498 (SD $11,668), respectively, p<0.01] resulting in a difference of $667. This was driven by medical costs [$5520 (SD $10,505) vs. $5222 (SD $10,689), respectively, p<0.01] a $298 difference, and total prescription costs [$2646 (SD $3262) vs. $2276 (SD $3907), respectively, p<0.01] a $369 difference.

LIMITATIONS

The study design demonstrates associations only and cannot establish causal relationships. Further, relevant DDEs were not included if concurrent consumption occurred outside the index period and when CYP450 substances were consumed that are not reflected in pharmacy claims (herbals, over-the-counter medications).

CONCLUSION

Since concurrent exposure to DDEs with the potential to cause PK DDIs may be relatively common, policy decisions-makers should consider the use of long-acting opioids that are not metabolized through the CYP450 pathway.