Opioid Metabolism

Catalogue of Somatic Mutations in Cancer Database and Structural Modeling Analysis of CYP2D6 Mutations in Human Cancers

Single nucleotide polymorphisms (SNPs) in cytochrome P450 (CYP450) enzymes alter the metabolism of a variety of drugs. Numerous medications, including chemotherapies, are metabolized by CYP450 enzymes, making the expression of this suite of enzymes in tumor cells relevant to prescription regimens for patients with cancer. We analyzed the characteristics of mutations of the cytochrome P450 2D6 (CYP2D6) enzymes in cancer patients obtained from the Catalogue of Somatic Mutations in Cancer (COSMIC), including mutation type, age of the patient, tissue type, and histology. Mutations were analyzed through the Cancer-Related Analysis of Variants Toolkit (CRAVAT) software along with cancer-specific high-throughput annotation of somatic mutations (CHASMplus) and variant effect scoring tool (VEST4) algorithms to determine the likelihood of being a driver and/or pathogenic mutation. For mutations with significant CHASMplus and VEST4 scores, structural analysis of each corresponding mutant protein was performed. The effect of each mutation was evaluated for its impact on the overall protein stability and ligand binding using Foldit Standalone and SwissDock, respectively. Structural analysis revealed that several missense mutations in CYP2D6 resulted in altered stability after energy minimization. Three missense mutations of CYP2D6 significantly altered docking stability, and those located on alpha helices near the docking site had a more significant impact than those not found in secondary protein structures. In conclusion, we have identified a series of mutations to CYP2D6 enzymes with possible relevance to cancer pathologies. SIGNIFICANCE STATEMENT: CYP2D6 is responsible for the metabolism of many anticancer drugs. This study identified and characterized a series of mutations in the CYP2D6 enzyme that occurred in tumors. We found it likely that many of these mutations would alter enzyme function, leading to changes in drug metabolism in the tumor. We provide a basis for predicting the likelihood of a patient carrying these mutations to identify patients who may benefit from a precision medicine approach to drug selection and dosing.

The potential impact of CYP and UGT drug-metabolizing enzymes on brain target site drug exposure

Drug metabolism is one of the critical determinants of drug disposition throughout the body. While traditionally associated with the liver, recent research has unveiled the presence and functional significance of drug-metabolizing enzymes (DMEs) within the brain. Specifically, cytochrome P-450 enzymes (CYPs) and UDP-glucuronosyltransferases (UGTs) enzymes have emerged as key players in drug biotransformation within the central nervous system (CNS). This comprehensive review explores the cellular and subcellular distribution of CYPs and UGTs within the CNS, emphasizing regional expression and contrasting profiles between the liver and brain, humans and rats. Moreover, we discuss the impact of species and sex differences on CYPs and UGTs within the CNS. This review also provides an overview of methodologies for identifying and quantifying enzyme activities in the brain. Additionally, we present factors influencing CYPs and UGTs activities in the brain, including genetic polymorphisms, physiological variables, pathophysiological conditions, and environmental factors. Examples of CYP- and UGT-mediated drug metabolism within the brain are presented at the end, illustrating the pivotal role of these enzymes in drug therapy and potential toxicity. In conclusion, this review enhances our understanding of drug metabolism's significance in the brain, with a specific focus on CYPs and UGTs. Insights into the expression, activity, and influential factors of these enzymes within the CNS have crucial implications for drug development, the design of safe drug treatment strategies, and the comprehension of drug actions within the CNS. To that end, CNS pharmacokinetic (PK) models can be improved to further advance drug development and personalized therapy.

Hydrocodone, Oxycodone, and Morphine Metabolism and Drug-Drug Interactions

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug-drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5'-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT: A review of the literature focusing on drug-drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Biomarker selection strategies based on compound stability in wastewater-based epidemiology

The specific compositions of human excreta in sewage can be used as biomarkers to indicate the disease prevalence, health status, and lifestyle of the population living in the investigated catchment. It is important for guiding and evaluating public health policies as well as promoting human health development. Among several parameters of wastewater-based epidemiology (WBE), the decay of biomarkers during transportation in sewer and storage plays a crucial role in the back-calculation of population consumption. In this paper, we summarized the stability data of common biomarkers in storage at different temperatures and in-sewer transportation. Among them, cardiovascular drugs and antidiabetic drugs are very stable which can be used as biomarkers; most of the illicit drugs are stable except for cocaine, heroin, and tetrahydrocannabinol which could be substituted by their metabolites as biomarkers. There are some losses for part of antibiotics and antidepressants even in frozen storage. Rapid detection of contagious viruses is a new challenge for infectious disease control. With the deeper and broader study of biomarkers, it is expected that the reliable application of the WBE will be a useful addition to epidemiological studies.

Metabolic clearance of select opioids and opioid antagonists using hepatic spheroids and recombinant cytochrome P450 enzymes

The opioid crisis is a pressing public health issue, exacerbated by the emergence of more potent synthetic opioids, particularly fentanyl and its analogs. While competitive antagonists exist, their efficacy against synthetic opioids is largely unknown. Furthermore, due to the short durations of action of current antagonists, renarcotization remains a concern. In this study, metabolic activity was characterized for fentanyl-class opioids and common opioid antagonists using multiple in vitro systems, namely, cytochrome P450 (CYP) enzymes and hepatic spheroids, after which an in vitro-in vivo correlation was applied to convert in vitro metabolic activity to predictive in vivo intrinsic clearance. For all substrates, intrinsic hepatic metabolism was higher than the composite of CYP activities, due to fundamental differences between whole cells and single enzymatic reactions. Of the CYP isozymes investigated, 3A4 yielded the highest absolute and relative metabolism across all substrates, with largely negligible contributions from 2D6 and 2C19. Comparative analysis highlighted elevated lipophilicity and diminished CYP3A4 activity as potential considerations for the development of more efficacious opioid antagonists. Finally, antagonists with a high degree of molecular similarity exhibited comparable clearance, providing a basis for structure-metabolism relationships. Together, these results provide multiple screening criteria for early stage drug discovery involving opioid countermeasures.

Changes in Sewage Sludge Chemical Signatures During a COVID-19 Community Lockdown, Part 1: Traffic, Drugs, Mental Health, and Disinfectants

The early months of the COVID-19 pandemic and the associated shutdowns disrupted many aspects of daily life and thus caused changes in the use and disposal of many types of chemicals. While records of sales, prescriptions, drug overdoses, and so forth provide data about specific chemical uses during this time, wastewater and sewage sludge analysis can provide a more comprehensive overview of chemical changes within a region. We analyzed primary sludge from a wastewater-treatment plant in Connecticut, USA, collected March 19 to June 30, 2020. This time period encompassed the first wave of the pandemic, the initial statewide stay at home order, and the first phase of reopening. We used liquid chromatography-high-resolution mass spectrometry and targeted and suspect screening strategies to identify 78 chemicals of interest, which included pharmaceuticals, illicit drugs, disinfectants, ultraviolet (UV) filters, and others. We analyzed trends over time for the identified chemicals using linear trend analyses and multivariate comparisons (p < 0.05). We found trends related directly to the pandemic (e.g., hydroxychloroquine, a drug publicized for its potential to treat COVID-19, had elevated concentrations in the week following the implementation of the US Emergency Use Authorization), as well as evidence for seasonal changes in chemical use (e.g., increases for three UV-filter compounds). Though wastewater surveillance during the pandemic has largely focused on measuring severe acute respiratory syndrome-coronavirus-2 RNA concentrations, chemical analysis can also show trends that are important for revealing the public and environmental health effects of the pandemic. Environ Toxicol Chem 2022;41:1179-1192. © 2021 SETAC.

Changes in Sewage Sludge Chemical Signatures During a COVID-19 Community Lockdown, Part 1: Traffic, Drugs, Mental Health, and Disinfectants

The early months of the COVID-19 pandemic and the associated shutdowns disrupted many aspects of daily life and thus caused changes in the use and disposal of many types of chemicals. While records of sales, prescriptions, drug overdoses, and so forth provide data about specific chemical uses during this time, wastewater and sewage sludge analysis can provide a more comprehensive overview of chemical changes within a region. We analyzed primary sludge from a wastewater-treatment plant in Connecticut, USA, collected March 19 to June 30, 2020. This time period encompassed the first wave of the pandemic, the initial statewide stay at home order, and the first phase of reopening. We used liquid chromatography-high-resolution mass spectrometry and targeted and suspect screening strategies to identify 78 chemicals of interest, which included pharmaceuticals, illicit drugs, disinfectants, ultraviolet (UV) filters, and others. We analyzed trends over time for the identified chemicals using linear trend analyses and multivariate comparisons (p < 0.05). We found trends related directly to the pandemic (e.g., hydroxychloroquine, a drug publicized for its potential to treat COVID-19, had elevated concentrations in the week following the implementation of the US Emergency Use Authorization), as well as evidence for seasonal changes in chemical use (e.g., increases for three UV-filter compounds). Though wastewater surveillance during the pandemic has largely focused on measuring severe acute respiratory syndrome-coronavirus-2 RNA concentrations, chemical analysis can also show trends that are important for revealing the public and environmental health effects of the pandemic. Environ Toxicol Chem 2022;41:1179-1192. © 2021 SETAC.

Pharmacokinetic Characterisation and Comparison of Bioavailability of Intranasal Fentanyl, Transmucosal, and Intravenous Administration through a Three-Way Crossover Study in 24 Healthy Volunteers

Background

For more than 60 years, the synthetic opioid fentanyl has been widely used in anaesthesia and analgesia. While the intravenous formulation is primarily used for general anaesthesia and intensive care settings, the drug's high lipophilic properties also allow various noninvasive routes of administration. Published data suggest that intranasal administration is also attractive for use as intranasal patient-controlled analgesia (PCA). A newly developed intranasal fentanyl formulation containing 47 μg fentanyl, intravenous fentanyl, and oral transmucosal fentanyl citrate were characterised, and bioavailability was compared to assess the suitability of the intranasal formulation for an intranasal PCA product.

Methods

27 healthy volunteers were enrolled in a single-centre, open-label, randomised (order of treatments), single-dose study in a three-period crossover design. The pharmacokinetics of one intranasal puff of fentanyl formulation (47 μg, 140 mL per puff), one short intravenous infusion of 50 μg fentanyl, and one lozenge with an integrated applicator (200 μg fentanyl) were studied, and bioavailability was calculated. Blood samples were collected over 12 hours, and plasma concentrations of fentanyl were determined by HPLC with MS/MS detection.

Results

24 volunteers completed the study. The geometric mean of AUC_0-tlast was the highest with oral transmucosal administration (1106 h ∗ pg/ml, CV% = 32.86), followed by intravenous (672 h ∗ pg/ml, CV% = 32.18) and intranasal administration (515 h ∗ pg/ml, CV% = 30.10). C _max was 886 pg/ml (CV% = 59.38) for intravenous, 338 pg/ml (CV% = 45.61) for intranasal, and 310 pg/ml (CV% = 29.58) for oral transmucosal administration. t _max was shortest for intravenous administration (0.06 h, SD = 0.056), followed by intranasal (0.21 h, SD = 0.078) and oral transmucosal administration (1.20 h, SD = 0.763). Dose-adjusted absolute bioavailability was determined to be 74.70% for the intranasal formulation and 41.25% for the oral transmucosal product. In total, 38 adverse events (AEs) occurred. Fourteen AEs were potentially related to the investigational items. No serious AE occurred.

Conclusion

Pharmacokinetic parameters and bioavailability of the investigated intranasal fentanyl indicated suitability for its intended use as an intranasal PCA option.

Use of opioids in patients with cancer with hepatic impairment-a systematic review

PURPOSE

Opioids are recommended for moderate-to-severe cancer pain; however, in patients with cancer, impaired hepatic function can affect opioid metabolism. The aim of this systematic review was to evaluate the evidence for the use of opioids in patients with cancer with hepatic impairment.

METHODS

A systematic review was conducted and the following databases searched: AMED (-2021), MEDLINE (-2021), EMBASECLASSIC + EMBASE (-2021) and Cochrane Central Register of Controlled Trials (-2021). Eligible studies met the following criteria: patients with cancer-related pain, taking an opioid (as defined by the WHO Guidelines for the pharmacological and radiotherapeutic management of cancer pain in adults and adolescents); >18 years of age; patients with hepatic impairment defined using recognised or study-defined definitions; clinical outcome hepatic impairment related; and primary studies. All eligible studies were appraised using the Grading of Recommendations Assessment, Development and Evaluation system.

RESULTS

Three studies (n=95) were eligible but heterogeneity meant meta-analysis was not possible. Each individual study focused on only one each of oxycodone±hydrocotarnine, oxycodone/naloxone and morphine. No recommendations could be formulated on the preferred opioid in patients with hepatic impairment.

CONCLUSIONS

Morphine is the preferred opioid in hepatic impairment owing to clinical experience and pharmacokinetics. This review, however, found little clinical evidence to support this. Dose adjustments of morphine and the oxycodone formulations reviewed remain necessary in the absence of quality evidence. Overall, the quality of existing evidence on opioid treatments in cancer pain and hepatic impairment is low and there remains a need for high-quality clinical studies examining this.

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.

Obstructive sleep apnoea and polymorphisms: implications for anaesthesia care

With a worldwide obesity pandemic, the incidence of obstructive sleep apnoea (OSA) is increasing; obesity is the most significant risk factor in children. Increasing evidence suggests that OSA is in part mediated through markers of inflammation. Systemic and pulmonary hypertension, right ventricular hypertrophy, prediabetes, and other conditions are common. Adenotonsillectomy improves only ~70% of children; 30% require other interventions, e.g. weight loss programs. The gold standard for diagnosis is a sleep-polysomnogram which are expensive and not readily available. The McGill oximetry score (saw-tooth desaturations during obstruction and arousal) is more cost-effective. Repeated episodes of desaturation alter the opioid receptors such that analgesia is achieved at much lower levels of opioid than in patients undergoing the same procedure but without OSA. This response is of great concern because a standard dose of opioids may be a relative overdose. Polymorphism variations in cytochrome CYP2D6 have major effects upon drug efficacy and side effects. Codeine, hydrocodone, oxycodone, and tramadol are all prodrugs that require CYP2D6 for conversion to the active compound. CYP2D6 is quite variable and patients can be divided into 4 classes: For codeine for example, poor metaboliser (PM) have virtually no conversion to morphine, intermediate metabolisers (IM) have some conversion to morphine, extensive metabolisers (EM) have a normal rate of conversion to morphine, and ultra-rapid metabolisers (RM) convert excessive amounts of codeine to morphine. Such variations result in some patients achieving no analgesia because there is reduced conversion to the active moiety whereas others convert an excessive amount of drug to the active compound thus resulting in relative or actual overdose despite appropriate dosing. Thus, OSA patients may have both opioid sensitivity due to recurrent desaturations and altered drug metabolism resulting in higher than intended blood levels of opioid. OSA patients should only receive one-third to half the usual dose of opioid. In those under the age of six, an effort should be made to avoid opioids altogether and use opioid sparing techniques such as alternating acetaminophen and ibuprofen.

Electrochemical Detection of Oxycodone and Its Main Metabolites with Nafion-Coated Single-Walled Carbon Nanotube Electrodes

Oxycodone is a strong opioid frequently used as an analgesic. Although proven efficacious in the management of moderate to severe acute pain and cancer pain, use of oxycodone imposes a risk of adverse effects such as addiction, overdose, and death. Fast and accurate determination of oxycodone blood concentration would enable personalized dosing and monitoring of the analgesic as well as quick diagnostics of possible overdose in emergency care. However, in addition to the parent drug, several metabolites are always present in the blood after a dose of oxycodone, and to date, there is no electrochemical data available on any of these metabolites. In this paper, a single-walled carbon nanotube (SWCNT) electrode and a Nafion-coated SWCNT electrode were used, for the first time, to study the electrochemical behavior of oxycodone and its two main metabolites, noroxycodone and oxymorphone. Both electrode types could selectively detect oxycodone in the presence of noroxycodone and oxymorphone. However, we have previously shown that addition of a Nafion coating on top of the SWCNT electrode is essential for direct measurements in complex biological matrices. Thus, the Nafion/SWCNT electrode was further characterized and used for measuring clinically relevant concentrations of oxycodone in buffer solution. The limit of detection for oxycodone with the Nafion/SWCNT sensor was 85 nM, and the linear range was 0.5–10 μM in buffer solution. This study shows that the fabricated Nafion/SWCNT sensor has potential to be applied in clinical concentration measurements.

Hip Fracture Risk among Hemodialysis-Dependent Patients Prescribed Opioids and Gabapentinoids

BACKGROUND

Despite opioids' known association with hip fracture risk in the general population, they are commonly prescribed to patients with ESKD. Whether use of opioids or gabapentinoids (also used to treat pain in patients with ESKD) contributes to hip fracture risk in patients with ESKD on hemodialysis remains unknown.

METHODS

In a case-control study nested within the US Renal Data System, we identified all hip fracture events recorded among patients dependent on hemodialysis from January 2009 through September 2015. Eligible cases were risk-set matched on index date with ten eligible controls. We required >1 year of Medicare Parts A and B coverage and >3 years of part D coverage to study cumulative longer-term exposure. To examine new, short-term exposure, we selected individuals with >18 months of Part D coverage and no prior opioid or gabapentinoid use between 18 and 7 months before index. We used conditional logistic regression to estimate unadjusted and multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (95% CI).

RESULTS

For the longer-term analyses, we identified 4912 first-time hip fracture cases and 49,120 controls. Opioid use was associated with increased hip fracture risk (adjusted OR, 1.39; 95% CI, 1.26 to 1.53). Subgroups of low, moderate, and high use yielded adjusted ORs of 1.33 (95% CI, 1.20 to 1.47), 1.53 (95% CI, 1.36 to 1.72), and 1.66 (95% CI, 1.45 to 1.90), respectively. The association with hip fractures was also elevated with new, short-term use (adjusted OR, 1.38; 95% CI, 1.25 to 1.52). There were no associations between gabapentinoid use and hip fracture.

CONCLUSIONS

Among patients dependent on hemodialysis in the United States, both short-term and longer-term use of opioid analgesics were associated with hip fracture events.

Chronic Methadone Use Alters the CD8+ T Cell Phenotype In Vivo and Modulates Its Responsiveness Ex Vivo to Opioid Receptor and TCR Stimuli

Endogenous opioid peptides are released at sites of injury, and their cognate G protein-coupled opioid receptors (ORs) are expressed on immune cells. Although drugs of misuse appropriate ORs, conflicting reports indicate immunostimulatory and immunosuppressive activity, in that opioid users have elevated infection risk, opioids activate innate immune cells, and opioids attenuate inflammation in murine T cell-mediated autoimmunity models. The i.v. use of drugs transmits bloodborne pathogens, particularly viruses, making the study of CD8⁺ T cells timely. From a cohort of nonuser controls and methadone users, we demonstrate, via t-Stochastic Neighbor Embedding and k-means cluster analysis of surface marker expression, that chronic opioid use alters human CD8⁺ T cell subset balance, with notable decreases in T effector memory RA⁺ cells. Studying global CD8⁺ T cell populations, there were no differences in expression of OR and several markers of functionality, demonstrating the need for finer analysis. Purified CD8⁺ T cells from controls respond to opioids ex vivo by increasing cytoplasmic calcium, a novel finding for OR signal transduction, likely because of cell lineage. CD8⁺ T cells from controls exposed to μ-OR agonists ex vivo decrease expression of activation markers CD69 and CD25, although the same markers are elevated in μ-OR-treated cells from methadone users. In contrast to control cells, T cell subsets from methadone users show decreased expression of CD69 and CD25 in response to TCR stimulus. Overall, these results indicate a direct, selective role for opioids in CD8⁺ T cell immune regulation via their ability to modulate cell responses through the opioid receptors and TCRs.

Clinical Pharmacology Considerations in Pain Management in Patients with Advanced Kidney Failure

Pain is common and poorly managed in patients with advanced CKD, likely due to both under and over prescription of appropriate analgesics. Poorly managed pain contributes to patients' poor quality of life and excessive health care use. There is tremendous variability within and between countries in prescribing patterns of analgesics, suggesting that factors other than patient characteristics account for these differences. This article discusses the pharmacologic management of acute and chronic pain in patients with advanced CKD, and the role analgesics, including opioids, play in the overall approach to pain management.

Phylogenetic analysis of the cytochrome P450 (CYP450) nucleotide sequences of the horse and predicted CYP450s of the white rhinoceros (Ceratotherium simum) and other mammalian species

Background

The plight of the white rhinoceros (Ceratotherium simum) and the increasing need of treatment options for injured poaching victims led to the necessity to expand the knowledge on applicable drugs in this endangered species. With very little information available on drug pharmacokinetics in rhino, veterinarians have to rely on information generated from other species. The horse being a closely related species, has served as the model for dose extrapolations. However, from recent research on enrofloxacin and carprofen, the white rhino showed considerable differences in the pharmacokinetic properties of these drugs in comparison to the horse. While the reason for the differences is unknown, a likely cause may be a difference in present cytochrome P450 (CYP450), which may result in the rhino being genetically deficient in certain enzyme families.

Methods

For this paper we assess the degree of similarity of the CYP genome sequences across the different species, using BLAT (BLAST-like alignment tool) for the alignment of the nucleotide sequences of the equine CYP450 with potential homologous nucleotide sequences of the published database from white rhinos and other mammalian species (cow, pig, dog, sheep, elephant, mouse and human).

Results

The white rhino nucleotide sequences were 90.74% identical to the equine sequences. This was higher than the degree of similarity between any of the other evaluated species sequences. While no specific CYP family were found to be deficient in the published rhino genome, the horse genome contained additional genetic sequence for a larger number of iso-enzymes that were not present in the rhino.

Discussion

In pharmacokinetic study, it is well known that absence of a metabolic enzyme will result in constraints in drug metabolism and drug elimination. While this was our speculation, comparison to the horse and other mammalian species indicate that all the described CYP genes required for metabolism are present within the rhino genome. These results leave functional differences in enzyme activity and a lack of isoenzymes as the likely reason for the constraint in drug metabolism. Despite a more than 90% similarity of the equine and rhino gene sequences, seemingly small differences can have major effects on drug metabolism. Thus, in spite of the close anatomical relationship, the rhino should not simply be treated like a big horse.

Why Are the Majority of Active Compounds in the CNS Domain Natural Products? A Critical Analysis

Small-molecule natural products (NPs) have a long and successful track record of providing first-in-class drugs and pharmacophore (scaffolds) in all therapeutic areas, serving as a bridge between modern and traditional medicine. This trajectory has been remarkably successful in three key areas of modern therapeutics: cancers, infections, and CNS diseases. Beginning with the discovery of morphine 200 years ago, natural products have remained the primary source of new drugs/scaffolds for CNS diseases. In this perspective, we address the question: why are the majority of active compounds in the CNS domain natural products? Our analysis indicates that ∼84% approved drugs for CNS diseases are NPs or NP-inspired, and interestingly, 20 natural products provided more than 400 clinically approved CNS drugs. We have discussed unique physicochemical properties of NPs and NP-inspired vis-à-vis synthetic drugs, isoform selectivity, and evolutionary relationship, providing a rationale for increasing focus on natural product driven discovery for next-generation drugs for neurodegenerative diseases.

Patterns of NSAIDs Use and Their Association with Other Analgesic Use in CKD

BACKGROUND AND OBJECTIVES

Avoiding nonsteroidal anti-inflammatory drugs is important for safe CKD care. This study examined nonsteroidal anti-inflammatory drug use patterns and their association with other analgesic use in CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Chronic Renal Insufficiency Cohort Study is an observational cohort study that enrolled 3939 adults ages 21-74 years old with CKD between 2003 and 2008 using age-based eGFR inclusion criteria. Annual visits between June of 2003 and December of 2011 were organized into 15,917 visit-pairs (with an antecedent and subsequent visit) for 3872 participants with medication information. Demographics, kidney function, and clinical factors were ascertained along with report of nonsteroidal anti-inflammatory drug or other analgesic use in the prior 30 days.

RESULTS

In our study, 24% of participants reported nonsteroidal anti-inflammatory drug use at baseline or at least one follow-up study visit. Having a 10 ml/min per 1.73 m2 higher eGFR level at an antecedent visit was associated with higher odds of starting nonsteroidal anti-inflammatory drugs at a subsequent visit (odds ratio, 1.44; 95% confidence interval, 1.34 to 1.56). Seeing a nephrologist at the antecedent visit was associated with lower odds of starting or staying on nonsteroidal anti-inflammatory drugs at a subsequent visit (odds ratio, 0.70; 95% confidence interval, 0.56 to 0.87 and odds ratio, 0.61; 95% confidence interval, 0.46 to 0.81, respectively). Starting and stopping nonsteroidal anti-inflammatory drugs were both associated with higher odds of increasing the number of other analgesics (odds ratio, 1.52; 95% confidence interval, 1.25 to 1.85 and odds ratio, 1.78; 95% confidence interval, 1.39 to 2.28, respectively) and higher odds of increasing the number of opioid analgesics specifically (odds ratio, 1.92; 95% confidence interval, 1.48 to 2.48 and odds ratio, 1.46; 95% confidence interval, 1.04 to 2.03, respectively).

CONCLUSIONS

Nonsteroidal anti-inflammatory drug use is common among patients with CKD but less so among those with worse kidney function or those who see a nephrologist. Initiation or discontinuation of nonsteroidal anti-inflammatory drugs is often associated with supplementation with or replacement by, respectively, other analgesics, including opioids, which introduces possible drug-related problems when taking these alternative analgesics.

Gene expression study of phase I and II metabolizing enzymes in RPTEC/TERT1 cell line: application in in vitro nephrotoxicity prediction

1. The phase I and II metabolizing enzymes of kidneys play an important role in the metabolism of xenobiotic as well as endogenous compounds and proximal tubules of kidney constitute high concentration of these metabolizing enzymes compared with the other parts. 2. It has been shown previously that differential enzyme expression among human and rodent/non-rodent species can be a roadblock in drug discovery and development process. Currently, proximal tubule cell lines of human origin such as RPTEC/TERT1 and HK-2 are used to understand the pathophysiology of kidney diseases, therapeutic efficacy of drugs, and nephrotoxicity of compounds. 3. The purpose of the present study is to understand the metabolic enzymes present in RPTEC/TERT1 and HK-2 cell lines that would help to interpret and predict probable in vitro behavior of the molecule being tested. 4. We analyzed the expression of phase I and II metabolizing enzymes of RPTEC/TERT1 and HK-2 cell lines. We found equal expression of CYP1B1, 2J2, 3A4, 3A5, UGT1A9, SULT2A1 and GSTA, higher expression of 2B6, 2D6, 4A11, 4F2, 4F8, 4F11, UGT2B7, SULT1E1 in RPTEC/TERT1 and absence of GSTT in RPTEC/TERT1 compared to HK-2 at mRNA level. Such differences can affect the outcome of in vitro nephrotoxicity prediction.

Painful Reality: Inappropriate Provider Management of Pain as a Determinant of Health Care Avoidance

Although pain is often characterized as a subjective, highly individualized phenomenon, in fact, numerous elements which are simply biological in nature underlie interpersonal differences in pain experience that influence the effectiveness of provider pain management. Elements acting at the level of tissues and cells include signal-transmitting molecules in pain pathways; elements acting at the level of the whole person comprise entire brain networks and anatomic elements fostering pain vulnerability. However, knowledge of these elements and translation of such knowledge into practical means for relieving patient pain is dismayingly sparse across the total spectrum of health care professionals. A serious consequence of this knowledge and action gap is that isolated, or worse yet, repeated, pain experiences may lead to profound mistrust of the health care system and its providers and to health care avoidance (e.g., mammography). This article outlines a biologic knowledge base and proposed remedies to improve pain management across the entire domain of health care. Key components of this approach include enhanced education for providers and informational outreach to health care consumers, clarifying pain mechanisms to both constituencies. Moreover, increased accountability within the health care system is needed, both in knowing and applying well-established biomedical knowledge and in best using technical and interpersonal skills necessary for effective pain management.

Evidence for Neurotoxicity Due to Morphine or Hydromorphone Use in Renal Impairment: A Systematic Review

BACKGROUND

Opioids are the mainstay of pain control for patients with chronic pain. Often, opioids with reported active metabolites, such as morphine and hydromorphone, are thought to increase the risk of neurotoxicity in renal impairment.

OBJECTIVES

To identify and assess the quality of evidence for neurotoxic effects in patients with renal impairment receiving morphine or hydromorphone.

METHODS

Systematic searches were conducted of the following databases from inception to December 2015: MEDLINE, CINAHL, EMBASE, in addition to hand-searching relevant review articles' citations. Studies were included if they reported neurotoxic effects of either morphine or hydromorphone for chronic or malignant pain in patients with renal impairment. Review articles and case reports were excluded. Narrative review was undertaken. The Grading of Recommendations, Assessment, Development and Evaluation approach was used to assess study quality.

RESULTS

Six original articles, three prospective and three retrospective studies were identified and assessed. No relevant randomized clinical trials were identified.

CONCLUSIONS

Although morphine and hydromorphone use may be associated with neurotoxic effects in patients with renal impairment, current evidence consists of very low-quality studies with conflicting findings. Clinicians may consider using either morphine or hydromorphone in mild-to-moderate renal impairment, while closely monitoring for neurotoxic effects, particularly when used in high doses and for extended duration.

Variable Patterns of Continuous Morphine Infusions at End of Life

BACKGROUND

Continuous morphine infusions (CMIs) treat pain and dyspnea at the end of life (EOL). CMIs may be initiated at an empiric rate and/or are rapidly escalated without proper titration.

OBJECTIVE

The study objective was to evaluate CMI patterns at the EOL.

METHODS

This single-center, retrospective chart review evaluated adult patients who died while receiving CMI at EOL. Patient demographics and opioid dosing information were extracted from an electronic medical record. Twenty-four hour IV morphine equivalent was calculated prior to CMI initiation and at the time of death.

RESULTS

Of the 190 patient charts, 63.2% (n=120) received no bolus doses prior to CMI initiation. Mean 24-hour IV morphine equivalent prior to CMI initiation was 49.3 mg (range: 0-1200 mg, SD 384.9) and at time of death was 267.1 mg (12.0-5193.2 mg, SD 442.2), representing an increase of +442%. Mean CMI starting rate was 3.3 mg/hour (0.4-30.0 mg/hour, SD 3.6) with titration at time of death to a mean of 7.7 mg/hour (0.4-70.0 mg/hour, SD 9.4), representing an increase of +130%. Mean number of CMI rate adjustments was 2.5 (0-5, SD 3.3); and number of bolus doses administered between titrations was 4.2 (0-27, SD 4.8). Mean time from CMI initiation to death was 15.5 hours (0.05-126.9 hours, SD 21.7). There was a negative association between rate of infusion increase per hour and total number of hours on CMI (r=-0.2, p=0.0062).

CONCLUSIONS

Hospitalized patients at EOL had a much higher 24-hour IV morphine equivalents and CMI rates at time of death compared to CMI initiation. Variability was observed in the number of CMI rate adjustments and the number of bolus doses administered.

Observations on the urine metabolic profile of codeine in pain patients

This retrospective data analysis explored the relationship between codeine and its metabolites morphine, hydrocodone and hydromorphone. The objectives were: (i) to determine urine concentrations and mole fractions of codeine and metabolites and (ii) to examine the effect of cytochrome P450 (CYP) 2D6 inhibition on metabolite mole fractions. De-identified urine specimens were collected between September 2010 and July 2011 and analyzed using LC-MS-MS to determine codeine, morphine, hydrocodone and hydromorphone concentrations. Geometric mean urine concentrations were 0.833, 0.085 and 0.055 for morphine, hydrocodone and hydromorphone, respectively. Mole fractions were 0.23, 0.025 and 0.014 for morphine, hydrocodone and hydromorphone, respectively. The fraction of excreted codeine in the urine increased (slope = 0.06 ± .01, R² = 0.02) with total moles. As the total amount of codeine and metabolites increased, the fraction of codeine increased, while the fraction of active metabolites decreased. CYP2D6 inhibition with paroxetine, fluoxetine, bupropion and methadone significantly decreased the fraction of morphine excreted. The prevalence of codeine metabolism to morphine was considerably higher than codeine to hydrocodone. The urine concentration of codeine excreted was the greatest, followed by morphine and hydrocodone. Subjects should be monitored during concomitant use of codeine and CYP2D6 inhibitors as this affects the amount of morphine metabolite formation.

Pharmacogenomics of opioids and perioperative pain management

Inadequate pain relief and adverse effects from analgesics remain common in children and adults during the perioperative period. Opioids are the most commonly used analgesics in children and adults to treat perioperative pain. Narrow therapeutic index and a large interpatient variability in response to opioids are clinically significant, with inadequate pain relief at one end of the spectrum and serious side effects, such as respiratory depression and excessive sedation due to relative overdosing, at the other end. Personalizing analgesia during the perioperative period attempts to maximize pain relief while minimizing adverse events from therapy. While various factors influence response to treatment among surgical patients, age, sex, race and pharmacogenetic differences appear to play major roles in predicting outcome. Genetic factors include a subset of genes that modulate the proteins involved in pain perception, pain pathway, analgesic metabolism (pharmacokinetics), transport and receptor signaling (pharmacodynamics). While results from adult genetic studies can provide direction for pediatric studies, they have limited direct applicability, as children's genetic predispositions to analgesic response may be influenced by developmental and behavioral components, altered sensitivity to analgesics and variation in gene-expression patterns. We have reviewed the available evidence on improving and personalizing pain management with opioids and the significance of individualizing analgesia, in order to maximize analgesic effect with minimal adverse effects with opioids. While the early evidence on individual genotype associations with pain, analgesia and opioid adverse outcome are promising, the large amount of conflicting data in the literature suggests that there is a need for larger and more robust studies with appropriate population stratification and consideration of nongenetic and other genetic risk factors. Although the clinical evidence and the prospect of being able to provide point-of-care genotyping to enable clinicians to deliver personalized analgesia for individual patients is still not available, positioning our research to identify all possible major genetic and nongenetic risk factors of an individual patient, advancing less expensive point-of-care genotyping technology and developing easy-to-use personalized clinical decision algorithms will help us to improve current clinical and economic outcomes associated with pain and opioid pain management.

Research priorities in geriatric palliative care: nonpain symptoms

Research addressing the burden, assessment, and management of nonpain symptoms associated with advanced illness in older adults is limited. While nonpain symptoms such as fatigue, sleep, dyspnea, anxiety, depression, cognitive impairment, nausea, and anorexia-cachexia are commonly noted by patients and clinicians, research quantifying their effects on quality of life, function, and other outcomes are lacking and there is scant evidence regarding management. Most available studies have focused on relatively narrow conditions (e.g., chemotherapy-induced nausea) and there are almost no data relevant to patients with multiple morbidities or multiple concurrent symptoms. Assessment and treatment of nonpain symptoms in older adults with serious illness and multiple comorbidities is compromised by the lack of data relevant to their care. Recommended research priorities address the documented high prevalence of distressing symptoms in older adults with serious illness, the unique needs of this population due to coexistence of multiple chronic conditions along with physiologic changes related to aging, the lack of evidence for effective pharmacologic and nonpharmacologic interventions, and the need for validated measures that are relevant across multiple care settings.

Drug testing for newborn exposure to illicit substances in pregnancy: pitfalls and pearls

Estimates of the prevalence of drug usage during pregnancy vary by region and survey tool used. Clinicians providing care to newborns should be equipped to recognize a newborn who has been exposed to illicit drugs during pregnancy by the effects the exposure might cause at the time of delivery and/or by drug testing of the newborn. The purpose of this paper is to provide an overview of the literature and assess the clinical role of drug testing in the newborn. Accurate recognition of a newborn whose mother has used illicit drugs in pregnancy cannot only impact decisions for healthcare in the nursery around the time of delivery, but can also provide a key opportunity to assess the mother for needed services. While drug use in pregnancy is not an independent predictor of the mother's ability to provide a safe and nurturing environment for her newborn, other issues that often cooccur in the life of a mother with a substance abuse disorder raise concerns for the safety of the discharge environment and should be assessed. Healthcare providers in these roles should advocate for unbiased and effective treatment services for affected families.

Prodrugs--from serendipity to rational design

The prodrug concept has been used to improve undesirable properties of drugs since the late 19th century, although it was only at the end of the 1950s that the actual term prodrug was introduced for the first time. Prodrugs are inactive, bioreversible derivatives of active drug molecules that must undergo an enzymatic and/or chemical transformation in vivo to release the active parent drug, which can then elicit its desired pharmacological effect in the body. In most cases, prodrugs are simple chemical derivatives that are only one or two chemical or enzymatic steps away from the active parent drug. However, some prodrugs lack an obvious carrier or promoiety but instead result from a molecular modification of the prodrug itself, which generates a new active compound. Numerous prodrugs designed to overcome formulation, delivery, and toxicity barriers to drug utilization have reached the market. In fact, approximately 20% of all small molecular drugs approved during the period 2000 to 2008 were prodrugs. Although the development of a prodrug can be very challenging, the prodrug approach represents a feasible way to improve the erratic properties of investigational drugs or drugs already on the market. This review introduces in depth the rationale behind the use of the prodrug approach from past to present, and also considers the possible problems that can arise from inadequate activation of prodrugs.

Individual differences in morphine and butorphanol analgesia: a laboratory pain study

OBJECTIVE

Responses to opioid analgesics are highly variable, and the understanding of contributing factors is limited. This laboratory study was designed to examine the contributions of sex and race to inter-individual variability in response to opioids.

DESIGN

A randomized, double-blind, mixed design was implemented in the evaluation of analgesic response to a µ-opioid agonist and mixed agonist-antagonist, using three well-validated experimental pain assays (thermal, pressure, and ischemic).

SUBJECTS

Participants included a total of 142 healthy subjects (76 men/66 women), 119 non-Hispanic whites and 23 African Americans.

INTERVENTION

Three sessions of pain testing were completed prior to and following an intravenous administration of morphine (0.08 mg/kg), butorphanol (0.016 mg/kg), and placebo (saline) in counterbalanced order.

OUTCOME MEASURES

A change score was calculated from the difference between the pre-drug and postdrug values. Three separate change scores (morphine, saline, and butorphanol) were computed for each experimental pain variable. Mixed-model analyses of covariance were performed on analgesic change scores.

RESULTS

Significant sex differences emerged for predrug pain measures with minimal differences for race. Sex differences in opioid analgesia were not demonstrated. However, significant race differences and race X drug interactions emerged for thermal, pressure, and ischemic pain measures. The pattern of results generally indicated that for pressure and ischemic pain, African American subjects showed greater analgesic responses to both medications compared with non-Hispanic whites. For thermal pain threshold, butorphanol but not morphine analgesia was greater for African American vs non-Hispanic whites.

CONCLUSIONS

Findings are among the first to demonstrate race differences in a laboratory study of opioid analgesia.

Sufentanil for chronic pain management

Sufentanil is a highly potent synthetic opioid that is approximately 1000-fold more potent than morphine and up to tenfold more potent than fentanyl. It is most commonly used by anesthesiologists to provide intraoperative analgesia. Although sufentanil is not yet approved for chronic pain management, it is being explored for chronic pain therapy. Owing to its physical properties, high potency, high lipid solubility, high therapeutic index and short duration of action, sufentanil has the potential to provide effective analgesia via multiple routes of administration. The superior pharmacokinetics of sufentanil make it ideal for treatment of breakthrough pain via the sublingual/buccal and nasal routes. Similarly, the transdermal route of sufentanil administration should provide analgesia for a prolonged period. The adverse effects of sufentanil are similar to those of other opioids that are commonly used for chronic pain management (e.g., fentanyl and morphine). Future research is necessary to define the role of sufentanil in the treatment of chronic pain.

Opioids for cancer pain: the challenge of optimizing treatment

During 2007, 11.7 million US men and women of all ages suffered from some form of invasive cancer. During their illness, at least 70% (8.2 million) will experience pain sufficiently severe to require chronic opioid treatment. Cancer-induced pain is usually described under 3 headings: acute pain, chronic pain, and breakthrough pain. Among patients with chronic, persistent cancer pain controlled by around-the-clock analgesics, there is a high prevalence of breakthrough pain-often precipitated by some form of physical activity. Breakthrough pain seems best treated by a powerful, fast-acting opioid such as intravenous morphine or transmucosal fentanyl. At present, opioids are virtually the only analgesics capable of controlling moderate and severe cancer pain. In recent years, a veritable arsenal of opioids with a wide range of pharmacologic properties has become available for use in different pain situations. The World Health Organization has developed a 3-step "analgesic ladder" to guide management of cancer pain, based on the pain's severity, estimated by means of a 1 to 10 numeric rating scale. As the severity of the pain escalates, more potent (World Health Organization Step III) opioids are used. When faced with a difficult case of cancer pain, the physician must choose-from an array of options-the safest and most effective opioid analgesic and the most appropriate delivery system. Such decisions require an adequate understanding of the available opioids and experience with their use. The pharmacodynamic response to a given opioid depends on the nature of the receptor to which the opioid binds and its affinity for the receptor. Morphine activates the μ-opioid receptors, resulting in not only analgesia and sedation, but also euphoria, respiratory depression, constipation, and pruritus. The existence of a number of opioid receptor subtypes, each with its own repertoire of responses, has given rise to the hope (as yet unrealized) that an opioid can be found (or engineered) that will selectively produce adequate analgesia and sedation without, at the same time, causing unwanted adverse effects. Furthermore, suitable neurostimulatory or neuroinhibitive methods involving the central nervous system are being sought that can amplify the analgesic action of opioids. In the search for antinociceptive agents as efficacious as currently available opioids, but without their troublesome adverse effects, the endogenous opioids, such as the endomorphins, are being examined as offering possible solutions to the adverse effect problem.