Pharmacokinetic drug interactions of morphine, codeine, and their derivatives: theory and clinical reality, part I

In vitro inhibitory effects of selumetinib on activity of human UDP-glucuronosyltransferases and prediction of in vivo drug-drug interactions

Selumetinib is an oral, effective, and selective tyrosine kinase inhibitor targeting mitogen-activated protein kinase 1 and 2 (MEK1/2), which is clinically active in multiple tumor types, such as neurofibromatosis type 1 (NF1), melanoma, gliomas and non-small cell lung cancer (NSCLC). The purpose of this article was to assess the effects of selumetinib on the activities of twelve human UDP-glucosyltransferases (UGTs) including UGT1A1, 1A3, 1A4, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B15, and 2B17, and its potential for inducing clinical drug-drug interactions (DDIs). The results demonstrated that selumetinib potently inhibited the activity of UGT2B7 through the mechanism of mixed inhibition with the inhibition constant value of 5.79 ± 0.65 μM. Furthermore, the plasma concentration of UGT2B7 substrate as the co-administered drug was predicted to be increased by at least 84 % when patients took selumetinib 75 mg twice daily, suggesting a high potential to induce clinical DDIs. Selumetinib exhibited weak inhibitory effects on other human UGTs and was unlikely to trigger off UGTs-mediated DDIs except for UGT2B7. Therefore, the combination of selumetinib with the substrate drug of UGT2B7 requires additional attention to avoid adverse events in clinical treatment.

Co-Evolution of Opioid and Adrenergic Ligands and Receptors: Shared, Complementary Modules Explain Evolution of Functional Interactions and Suggest Novel Engineering Possibilities

Cross-talk between opioid and adrenergic receptors is well-characterized and involves second messenger systems, the formation of receptor heterodimers, and the presence of extracellular allosteric binding regions for the complementary ligand; however, the evolutionary origins of these interactions have not been investigated. We propose that opioid and adrenergic ligands and receptors co-evolved from a common set of modular precursors so that they share binding functions. We demonstrate the plausibility of this hypothesis through a review of experimental evidence for molecularly complementary modules and report unexpected homologies between the two receptor types. Briefly, opioids form homodimers also bind adrenergic compounds; opioids bind to conserved extracellular regions of adrenergic receptors while adrenergic compounds bind to conserved extracellular regions of opioid receptors; opioid-like modules appear in both sets of receptors within key ligand-binding regions. Transmembrane regions associated with homodimerization of each class of receptors are also highly conserved across receptor types and implicated in heterodimerization. This conservation of multiple functional modules suggests opioid–adrenergic ligand and receptor co-evolution and provides mechanisms for explaining the evolution of their crosstalk. These modules also suggest the structure of a primordial receptor, providing clues for engineering receptor functions.

Endogenous and iatrogenic sources of variability in response to opioid therapy in Post-Surgical and injured orthopedic patients

BACKGROUND

Hydrocodone is the most prescribed opioid in the US. The objective was to evaluate associations between genetic, intrinsic, and extrinsic patient factors, plasma hydrocodone and metabolites, common side effects, and pain scores in a cohort of orthopedic surgery patients.

METHODS

Data for each patient was collected by review of the electronic hospital record (EHR), and patient interview. Patients were recruited from those with trauma or undergoing scheduled elective surgery for total knee replacement or total hip at the University of Louisville Hospital, Baptist East Hospital, and Jewish Hospital, Louisville, KY. Plasma opiate concentrations and a targeted genotyping panel was performed.

RESULTS

There were statistically significant correlations with daily (p < 0.001) and total dose (p = 0.002) of hydrocodone in hospital and duration of opioid therapy. The length of opioid administration was significantly shorter in CYP2D6 EM/UM versus CYP2D6 PM/IM patients (p = 0.018). Subjects with the OPRM1 c.118G variant were also on opioids longer (p = 0.022). The effect of co-administration of a CYP2D6 inhibitor had a significant effect on the length of opioid therapy (P < 0.001). And not surprisingly the effect of the inhibitor adjusted CYP2D6 phenotype was greater in both the hospital stay period and days of opioid use post hospital discharge (p < 0.001).

CONCLUSIONS

Based on this study, patients should be evaluated for the use of inhibitors of CYP2D6, during hydrocodone therapy can alter the phenotype of the patient (phenocopy) and increase the probability that the patient will be on opioids for longer periods of time.

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.

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.

Predicting inadequate postoperative pain management in depressed patients: A machine learning approach

Widely-prescribed prodrug opioids (e.g., hydrocodone) require conversion by liver enzyme CYP-2D6 to exert their analgesic effects. The most commonly prescribed antidepressant, selective serotonin reuptake inhibitors (SSRIs), inhibits CYP-2D6 activity and therefore may reduce the effectiveness of prodrug opioids. We used a machine learning approach to identify patients prescribed a combination of SSRIs and prodrug opioids postoperatively and to examine the effect of this combination on postoperative pain control. Using EHR data from an academic medical center, we identified patients receiving surgery over a 9-year period. We developed and validated natural language processing (NLP) algorithms to extract depression-related information (diagnosis, SSRI use, symptoms) from structured and unstructured data elements. The primary outcome was the difference between preoperative pain score and postoperative pain at discharge, 3-week and 8-week time points. We developed computational models to predict the increase or decrease in the postoperative pain across the 3 time points by using the patient’s EHR data (e.g. medications, vitals, demographics) captured before surgery. We evaluate the generalizability of the model using 10-fold cross-validation method where the holdout test method is repeated 10 times and mean area-under-the-curve (AUC) is considered as evaluation metrics for the prediction performance. We identified 4,306 surgical patients with symptoms of depression. A total of 14.1% were prescribed both an SSRI and a prodrug opioid, 29.4% were prescribed an SSRI and a non-prodrug opioid, 18.6% were prescribed a prodrug opioid but were not on SSRIs, and 37.5% were prescribed a non-prodrug opioid but were not on SSRIs. Our NLP algorithm identified depression with a F1 score of 0.95 against manual annotation of 300 randomly sampled clinical notes. On average, patients receiving prodrug opioids had lower average pain scores (p<0.05), with the exception of the SSRI+ group at 3-weeks postoperative follow-up. However, SSRI+/Prodrug+ had significantly worse pain control at discharge, 3 and 8-week follow-up (p < .01) compared to SSRI+/Prodrug- patients, whereas there was no difference in pain control among the SSRI- patients by prodrug opioid (p>0.05). The machine learning algorithm accurately predicted the increase or decrease of the discharge, 3-week and 8-week follow-up pain scores when compared to the pre-operative pain score using 10-fold cross validation (mean area under the receiver operating characteristic curve 0.87, 0.81, and 0.69, respectively). Preoperative pain, surgery type, and opioid tolerance were the strongest predictors of postoperative pain control. We provide the first direct clinical evidence that the known ability of SSRIs to inhibit prodrug opioid effectiveness is associated with worse pain control among depressed patients. Current prescribing patterns indicate that prescribers may not account for this interaction when choosing an opioid. The study results imply that prescribers might instead choose direct acting opioids (e.g. oxycodone or morphine) in depressed patients on SSRIs.

Effects of Oral Morphine on Dyspnea in Patients with Cancer: Response Rate, Predictive Factors, and Clinically Meaningful Change (CJLSG1101)

BACKGROUND

Although the efficacy of parenteral morphine for alleviating dyspnea has been previously demonstrated in several studies, little is known regarding the efficacy of oral morphine for dyspnea among patients with cancer, including its response rate and predictive factors of effectiveness. Therefore, the aim of this study was to clarify the effectiveness of oral morphine on dyspnea in patients with cancer and elucidate the predictive factors of its effectiveness.

SUBJECTS, MATERIALS, AND METHODS

In this multicenter prospective observational study, we investigated the change in dyspnea intensity in patients with cancer before and after the administration of oral morphine by using a visual analog scale (VAS). We also administered a self-assessment questionnaire to determine whether the patients believed oral morphine was effective.

RESULTS

Eighty patients were enrolled in the study, and 71 of these patients were eligible. The least square mean of the VAS scores for dyspnea intensity was 53.5 at baseline, which decreased significantly to 44.7, 40.8, and 35.0 at 30, 60, and 120 minutes after morphine administration, respectively. Fifty-four patients (76.1%) reported that oral morphine was effective on the self-assessment questionnaire. Among the background factors, a high score for "sense of discomfort" on the Cancer Dyspnea Scale (CDS) and a smoking history of fewer pack-years were associated with greater effectiveness.

CONCLUSION

Oral morphine was effective and feasible for treating cancer-related dyspnea. A higher score for "sense of discomfort" on the CDS and a smaller cumulative amount of smoking may be predictive factors of the effectiveness of oral morphine.

IMPLICATIONS FOR PRACTICE

This study demonstrated that oral morphine was effective in alleviating cancer-related dyspnea due to multiple factors including primary lung lesions, airway narrowing, and pleural effusion. Approximately 76% of patients reported that oral morphine was effective. A higher score for "sense of discomfort" on the Cancer Dyspnea Scale and a lower cumulative amount of smoking may be predictive factors for the effectiveness of oral morphine. Interestingly, respiratory rates in patients who reported the morphine to be effective decreased significantly after oral morphine administration, unlike the respiratory rates in "morphine-ineffective" patients.

Genomics Testing and Personalized Medicine in the Preoperative Setting

Pharmacogenomics (PGx) is the study of how individuals' personal genotypes may affect their responses to various pharmacologic agents. The application of PGx principles in perioperative medicine is fairly novel. Challenges in executing PGx programs into health care systems include physician buy-in and integration into usual clinical workflow, including the electronic health record. This article discusses the current evidence highlighting the potential of PGx with various drug categories (including opioids, nonopioid analgesics, sedatives, β-blockers, antiemetics, and anticoagulants) used in the perioperative process and the challenges of integrating PGx into a health care system and relevant workflows.

Pain Management in the Emergency Department: a Review Article on Options and Methods

CONTEXT

The aim of this review is to recognizing different methods of analgesia for emergency medicine physicians (EMPs) allows them to have various pain relief methods to reduce pain and to be able to use it according to the patient's condition and to improve the quality of their services.

EVIDENCE ACQUISITION

In this review article, the search engines and scientific databases of Google Scholar, Science Direct, PubMed, Medline, Scopus, and Cochrane for emergency pain management methods were reviewed. Among the findings, high quality articles were eventually selected from 2000 to 2018, and after reviewing them, we have conducted a comprehensive comparison of the usual methods of pain control in the emergency department (ED).

RESULTS

For better understanding, the results are reported in to separate subheadings including "Parenteral agents" and "Regional blocks". Non-opioids analgesics such as nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen are commonly used in the treatment of acute pain. However, the relief of acute moderate to severe pain usually requires opioid agents. Considering the side effects of systemic drugs and the restrictions on the use of analgesics, especially opioids, regional blocks of pain as part of a multimodal analgesic strategy can be helpful.

CONCLUSION

This study was designed to investigate and identify the disadvantages and advantages of using each drug to be able to make the right choices in different clinical situations for patients while paying attention to the limitations of the use of these analgesic drugs.

Ketorolac, Oxymorphone, Tapentadol, and Tramadol: A Comprehensive Review

Pain remains a tremendous burden on patients and for the health care system, with uncontrolled pain being the leading cause of disability in this country. There are a variety of medications that can be used in the treatment of pain, including ketorolac, oxymorphone, tapentadol, and tramadol. Depending on the clinical situation, these drugs can be used as monotherapy or in conjunction with other types of medications in a multimodal approach. A strong appreciation of pharmacologic properties of these agents and potential side effects is warranted for clinicians.

Oral Oxymorphone for Pain Management

Objective

To describe the pharmacology, safety and efficacy, and rationale for use of oral oxymorphone for the management of acute and chronic moderate-to-severe pain.

Data Sources

A PubMed/MEDLINE search (1966-March 2007) was conducted using the following terms: oral oxymorphone, oxymorphone, EN 3202, EN 3203, Opana, and Opana ER. Manufacturer-provided data (package inserts) and abstracts presented at the American Pain Society meetings (2003–2006) were also reviewed.

Study Selection and Data Extraction

Human studies evaluating the safety and efficacy of oral oxymorphone in pain management were considered; animal and non–English-language data were excluded.

Data Synthesis

Oral oxymorphone is a semisynthetic opioid agonist that is specific for the μ-opioid receptor and approved to treat both acute and chronic pain. Unlike other opioids, such as oxycodone, oxymorphone does not bind to the κ-opioid receptor. Due to extensive liver metabolism, oral oxymorphone is contraindicated in patients with moderate-to-severe hepatic impairment; however, no clinically significant CYP3A4, 2C9, or 2D6 mediated drug-drug interactions have been noted. Elderly patients may experience a 40% increase in plasma concentrations, while renally impaired patients may have a 57–65% increase in bioavailability. Food can increase the rate of absorption by as much as 50%, necessitating dosing either 1 hour before or 2 hours after a meal. Oxymorphone's primary adverse effects are similar to those of other opioids: nausea, vomiting, pruritus, pyrexia, and constipation.

Conclusions

Oxymorphone is an oral therapeutic option approved for the treatment of acute and chronic moderate-to-severe pain. Oxymorphone has a safety and efficacy profile similar to that of other commonly used pure opioids (morphine, oxycodone, hydromorphone). Like oxycodone and morphine, oxymorphone also has immediate-release and extended-re lease formulations. Since cost alone is not yet favorable for oxymorphone over oxycodone or morphine, further studies of comparative efficacy targeting potential advantages of oxymorphone over other opioids are necessary before considering it for addition to a formulary.

Pharmacokinetics cannot explain the increased effective dose requirement for morphine and midazolam in rats during their extended administration alone or in combination

Objectives

Chronic administration of morphine and midazolam, alone or in combination, can induce tolerance to their effects. Data showed that co-administration of morphine and midazolam increased effective dose requirement of morphine, exceeding that observed with morphine alone.

Methods

To elucidate the pharmacokinetic component to the tolerance, we administered midazolam (2 mg/kg) and morphine (10 mg/kg) alone or their combination daily to rats for 12 days followed by a pharmacokinetic study on day 13. On the study day, each animal received a single bolus dose of 5 mg/kg morphine, and 2 mg/kg of midazolam 30 s later. Multiple blood samples were obtained for 6 h. Plasma drug concentrations were assayed by mass spectrometry optimized for small samples.

Key findings

Mean morphine clearance was as follows: 22.2, 27.2, 26.0 and 23.4 l/h per kg in the saline–saline, saline–midazolam, saline–morphine and midazolam–morphine groups, respectively. Corresponding midazolam clearances were 32.8, 23.0, 22.2 and 31.1 l/h per kg. ANOVA indicated no significant differences among the four groups in the clearances, half-lives, and volumes of distribution. Morphine and midazolam clearances were significantly correlated (R2 = 0.48, P &lt; 0.001).

Conclusions

This animal model suggests that altered pharmacokinetics cannot explain tolerance evidenced as increased dose requirement for morphine or midazolam, when administered alone or combination, for extended periods.

Changes in activity patterns after the oral administration of brotizolam in institutionalized elderly patients with dementia

BACKGROUND

Little is known about the side effects of sedative-hypnotic agents in elderly dementia patients with sleep disorders. The present study describes activity pattern changes after a single dose of brotizolam in elderly patients with dementia.

METHODS

We conducted retrospective analysis of prospectively collected data from a case series at Asakayama Hospital (Osaka, Japan) between September 2008 and September 2009. Around-the-clock movements of dementia patients who were administered a single dose of brotizolam were recorded by the integrated circuit tag monitoring system during a 4-week baseline and 7-day peri-administration period. Diurnal and nocturnal activity levels and the onset times of the least-active and most-active phases were then measured.

RESULTS

Seven patients (four men, three women; age range 59-85 years) were analyzed. All seven patients had disturbed activity patterns during the peri-administration period. Compared with the pre-administration period, the incidence of reversed rest-activity pattern increased significantly in the post-administration period, as measured by the distance moved per hour (P < 0.000). Patients with advanced stages of dementia had prolonged and delayed activity responses.

CONCLUSIONS

Findings showed changes in activity levels and reversed active/resting phases after a single dose of brotizolam in elderly patients with dementia. Use of brotizolam in elderly patients with dementia, especially in advanced stages, calls for closer attention and longer observation periods.

The metabolism of opioid agents and the clinical impact of their active metabolites

BACKGROUND

The metabolism of opioids is critical to consider for multiple reasons. The most commonly prescribed opioid agents often have metabolites that are active and are the source of both analgesic activity and an increased incidence of adverse events. Many opioids are metabolized by cytochrome P450 enzymes. Polymorphisms in cytochrome P450 genes and inhibition or induction of cytochrome P450 enzymes by coadministered drugs may significantly impact the systemic concentration of opioids and their metabolites and the associated efficacy or adverse events.

METHODS

This is a narrative review of the metabolism of various opioids that will highlight the impact of their active metabolites, and the potential impact of cytochrome P450 activity on analgesic activity.

RESULTS

An understanding of "opioid metabolic machinery," cytochrome P450 activity, and drug-drug interactions in the context of opioid selection may benefit clinicians and patients alike.

CONCLUSIONS

A greater appreciation of the metabolism of commonly prescribed opioid analgesics and the impact of their active metabolites on efficacy and safety may aid prescribers in tailoring care for optimal outcomes.

Structural features of cytochromes P450 and ligands that affect drug metabolism as revealed by X-ray crystallography and NMR

Cytochromes P450 (P450s) play a major role in the clearance of drugs, toxins, and environmental pollutants. Additionally, metabolism by P450s can result in toxic or carcinogenic products. The metabolism of pharmaceuticals by P450s is a major concern during the design of new drug candidates. Determining the interactions between P450s and compounds of very diverse structures is complicated by the variability in P450-ligand interactions. Understanding the protein structural elements and the chemical attributes of ligands that dictate their orientation in the P450 active site will aid in the development of effective and safe therapeutic agents. The goal of this review is to describe P450-ligand interactions from two perspectives. The first is the various structural elements that microsomal P450s have at their disposal to assume the different conformations observed in X-ray crystal structures. The second is P450-ligand dynamics analyzed by NMR relaxation studies.

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.

Efflux transporters- and cytochrome P-450-mediated interactions between drugs of abuse and antiretrovirals

Multidrug regimens and corresponding drug interactions cause many adverse reactions and treatment failures. Drug efflux transporters: P-gp, MRP, BCRP in conjunction with metabolizing enzymes (CYPs) are major factors in such interactions. Most effective combination antiretrovirals (ARV) therapy includes a PI or a NNRTI or two NRTI. Coadministration of such ARV may induce efflux transporters and/or CYP3A4 resulting in sub-therapeutic blood levels and therapeutic failure due to reduced absorption and/or increased metabolism. A similar prognosis is true for ARV-compounds and drugs of abuse combinations. Morphine and nicotine enhance CYP3A4 and MDR1 expression in vitro. A 2.5 fold rise of cortisol metabolite was evident in smokers relative to nonsmokers. Altered functions of efflux transporters and CYPs in response to ARV and drugs of abuse may result in altered drug absorption and metabolism. Appropriate in vitro models can be employed to predict such interactions. Influence of genetic polymorphism, SNP and inter-individual variation in drug response has been discussed. Complexity underlying the relationship between efflux transporters and CYP makes it difficult to predict the outcome of HAART as such, particularly when HIV patients taking drugs of abuse do not adhere to HAART regimens. HIV(+) pregnant women on HAART medications, indulging in drugs of abuse, may develop higher viral load due to such interactions and lead to increase in mother to child transmission of HIV. A multidisciplinary approach with clear understanding of mechanism of interactions may allow proper selection of regimens so that desired therapeutic outcome of HAART can be reached without any side effects.

Case report: delirium due to a diltiazem-fentanyl CYP3A4 drug interaction

INTRODUCTION

Fentanyl and diltiazem are frequently used medications. Diltiazem inhibits cytochrome P450 3A4 isoenzymes. This can suppress fentanyl metabolism.

METHOD

We present a case of delirium after coadministration of fentanyl and diltiazem.

DISCUSSION

Cautious use is warranted while concomitantly administering fentanyl and diltiazem as this can potentiate fentanyl toxicity. Other 3A4 inhibitors include ketoconazole, erythromycin, nefazodone, ritonavir, delavirdine, aprepitant and imatinib. Psychosomatic medicine psychiatrists, pain and palliative care physicians and cardiologists in particular should be aware of this interaction.

Biological pathways and genetic variables involved in pain

PURPOSE

This paper summarizes current knowledge of pain-related and analgesic-related pathways as well as genetic variations involved in pain perception and management.

METHODS

The pain group of the GENEQOL Consortium was given the task of summarizing the current status of research on genetic variations in pain and analgesic efficacy. This review is neither exhaustive nor comprehensive; we focus primarily on single-nucleotide polymorphisms.

RESULTS

Two categories of potential genetic pain-perception pathways were identified: neurotransmission modulators and mechanisms that affect inflammation. Four categories were identified for analgesic efficacy: genes related to receptor interaction, modulation of opioid effects, metabolism, and transport. Various genetic variations involved in these pathways are proposed as candidate genetic markers for pain perception and for individual sensitivity to analgesics.

CONCLUSIONS

Candidate gene association studies have been used to provide evidence for the genetic modulation of pain perception and response to analgesics. However, the nature and range of genetic modulation of pain is not well addressed due to the limited number of patients and the limited number of genes and genetic variants investigated in studies to date. Moreover, personalized analgesic treatments will require a more complete understanding of the effects of genetic variants and gene-gene interactions in response to analgesics.

Ebastine in the light of CONGA recommendations for the development of third-generation antihistamines

In 2003 a consensus group on new-generation antihistamines (CONGA) defined the characteristics required for a third-generation H(1) antihistamine as there had been much controversy about this issue since the early 1990s. One of the antihistamines that had been claimed to belong to such a group is the second-generation antihistamine, ebastine. The objective of this review is to analyze the pharmacology of ebastine, in light of the CONGA recommendations for the development of new-generation antihistamines: (1) anti-inflammatory properties, (2) potency, efficacy and effectiveness, (3) lack of cardiotoxicity, (4) lack of drug interactions, (5) lack of CNS effects, and (6) pharmacological approach. Ebastine seems to have anti-inflammatory properties that help to ameliorate nasal congestion, though this has not yet been conclusively demonstrated. Its pharmacological-therapeutic profile does not differ greatly from that of other second-generation antihistamines. Its cardiac safety has been widely assessed and no cardiac toxicity has been found at therapeutic doses despite initial concerns. The risk of potentially relevant drug interactions has been investigated and ruled out. Ebastine does not produce sedation at therapeutic doses and drug interaction studies with classical CNS depressants have not demonstrated a synergistic effect. Pharmacologically, ebastine is an H(1) inverse agonist. Perhaps the answer to the quest for new-generation antihistamines lies not only in H(1) but in a combined approach with other histamine receptors.

CNS penetration of small molecules following local inflammation, widespread systemic inflammation or direct injury to the nervous system

AIMS

We sought to investigate effects of local and systemic inflammation on CNS permeability of small molecules and compare these to effects of direct injury to the nervous system.

MAIN METHODS

Evans blue was used to determine the integrity of the blood-brain barrier (BBB) following local inflammation, systemic inflammation, injury to the L5 spinal nerve or transient occlusion of the middle cerebral artery. In addition, three compounds having low, medium and high brain permeability (atenolol, morphine and oxycodone, respectively) were used. Following model establishment (4-hr post-carrageenan, 24-hr post-FCA, 2-, 4- and 24-hr post-LPS, 21 days post-nerve injury) compounds were administered and 30 min later the brain, spinal cord and blood removed. The plasma and tissue concentrations of compounds were quantified by LC/MS/MS.

KEY FINDINGS

Localized inflammation did not affect Evans blue penetration into the CNS but significantly increased morphine penetration into the spinal cord. Systemic inflammation increased the quantity of Evans blue in the CNS but also decreased the penetration of atenolol, morphine and oxycodone into the brain 4-hr post-insult. Nerve injury had no effect on Evans blue or compound penetration, while middle cerebral artery occlusion resulted in a large but short lived increase in Evans blue penetration into both the cortex and striatum.

SIGNIFICANCE

The presence of inflammation may affect the CNS penetration of some compounds but is unlikely to lead to a large non-selective BBB breakdown. As a result, it is appropriate to test for side-effects, and conduct brain pharmacokinetic determinations, in naïve rats.

Acute and chronic fentanyl administration causes hyperalgesia independently of opioid receptor activity in mice

Although mu-receptor opioids are clinically important analgesics, they can also paradoxically cause hyperalgesia independently of opioid receptor activity, presumably via the action of neuroexcitatory glucoronide metabolites. However, it is unknown whether the commonly used mu-receptor opioid analgesic fentanyl, which is not subject to glucuronidation, can also induce hyperalgesia independently of opioid receptor activity. Thus, here we examined whether fentanyl increases nociception on the tail-withdrawal test in CD-1 mice concurrently treated with the opioid receptor antagonist naltrexone or in opioid receptor triple knock-out mice lacking mu, delta, and kappa opioid receptors. For both groups, an acute fentanyl bolus dose (0.25mg/kg, s.c.) and continuous fentanyl infusion (cumulative daily dose: 10mg/kg) did not cause analgesia at any time. Instead, fentanyl significantly decreased withdrawal latencies relative to pre-drug values for the next 15-60 min and for six days, respectively. MK-801 blocked and reversed hyperalgesia caused by the acute injection and continuous infusion of fentanyl, respectively, in naltrexone-treated CD-1 mice, indicating the contribution of NMDA receptors to fentanyl hyperalgesia. These data show that the synthetic opioid fentanyl causes hyperalgesia independently of prior or concurrent opioid receptor activity or analgesia. Since the biotransformation of fentanyl does not yield any known pronociceptive metabolites, these data challenge assumptions regarding the role of neuroexcitatory metabolites in opioid-induced hyperalgesia.

Pain management principles in the critically ill

This article addresses conventional pharmacologic and nonpharmacologic treatment of pain in patients in ICUs. For the critically ill patient, opioids have been the mainstay of pain control. The optimal choice of opioid and dosing regimen for a specific patient varies depending on factors such as the pharmacokinetics and physicochemical characteristics of an opioid and the body's handling of the opioid, concomitant sedative regimen, potential or actual adverse drug events, and development of tolerance. The clinician must appreciate that favorable pharmacokinetic properties such as a short-elimination half-life do not necessarily translate into clinical advantages in the ICU setting. A variety of medications have been proposed as alternatives or adjuncts to the opioids for pain control that have unique considerations when contemplated for use in the critically ill patient. Most have been relatively unstudied in the ICU setting, and many have limitations with respect to availability of the GI route of administration in patients with questionable GI absorptive function. Nonpharmacologic, complementary therapies are low cost, easy to provide, and safe, and many clinicians can implement them with little difficulty or resources. However, the evidence base for their effectiveness is limited. At present, insufficient research evidence is available to support a broad implementation of nonpharmacologic therapies in ICUs.

Fatal and severe codeine intoxication in 3-year-old twins--interpretation of drug and metabolite concentrations

This work presents two cases of codeine intoxication in 3-year-old monozygotic twin brothers while treated with a codeine slow-release formulation. One child had to be admitted to the hospital, whereas the other one died at home after aspiration of gastric content. The concentrations of codeine and major metabolites including morphine and corresponding glucuronide conjugates were measured by liquid chromatography-tandem mass spectrometry in serum, urine, cerebrospinal fluid, and brain tissue, respectively. A genetic polymorphism study was carried out in order to determine the ability of the children to metabolize codeine by O-demethylation. A pharmacokinetic calculation was also performed to estimate the administered dose of codeine in question. High concentrations of all substances were found in samples of both children. The pharmacokinetic estimate suggests an overdose of codeine, and the possible reasons for the high opiate concentrations are discussed. Furthermore, the postmortem distribution--during and after resuscitation--might play a major role in the interpretation of postmortem concentration levels.

Mini-series: II. clinical aspects. clinically relevant CYP450-mediated drug interactions in the ICU

BACKGROUND

In the critically ill, multiple drug therapies for acute and chronic conditions are often used at the same time and adverse drug events occur frequently. Many pharmacological and disease-related factors, e.g. altered renal and hepatic function, catecholamine-related circulatory changes, altered drug volume of distribution, enteral versus parenteral feeding and morbid obesity, along with concomitant multiple drug regimens may account for the wide inter-individual variability in drug exposure and response in critically ill patients and for the high risk for drug-drug interactions to occur. The practicing intensivist must remain aware of the major mechanisms for drug-drug interactions, among which the drug-metabolizing enzyme inhibitory or induction potential of associated chemical entities are paramount. Metabolism-based drug-drug interactions are largely due to changes in levels of drug-metabolizing enzymes caused by one drug, leading to changes in the systemic exposure clearance of another. Among the numerous drug-metabolizing enzymes identified to date, the activity of cytochrome P450s (CYP450) is a critical determinant of drug clearance and appears to be involved in the mechanism of numerous clinically relevant drug-drug interactions observed in critically ill patients.

DISCUSSION

This manuscript will cover a practical overview of clinically relevant CYP450-mediated drug-drug interactions. Medications frequently used in the intensive care unit such as benzodiazepines, immunosuppressive agents, opioid analgesics, certain anticonvulsants, the azoles and macrolides have the potential to interact with CYP450-mediated metabolism and may lead to toxicity or therapeutic failure.

The side effects of morphine and hydromorphone patient-controlled analgesia

BACKGROUND

Despite "clinical lore" among health care providers that treatment with hydromorphone results in improved pain control and fewer adverse side effects, morphine continues to be the first-line medication for postoperative patient-controlled analgesia (PCA). In this study, we compared the efficacy and side-effect profiles of morphine and hydromorphone at concentrations producing equivalent drug effect measured by pain score and miosis.

METHODS

We conducted a prospective, randomized, double-blind trial of 50 general and gynecological surgery patients. Subjects were randomly assigned to receive either morphine (1 mg/mL) or hydromorphone (0.2 mg/mL) via PCA after surgery and were followed for a period of 8 h. The primary outcome was nausea. Secondary outcome variables were pruritus, vomiting, sedation, pain report, pupillary miosis, and patient satisfaction.

RESULTS

The side effect profile was not different between drugs. The incidence of nausea did not differ between morphine and hydromorphone-treated patients (1 h: 44% vs 52%, 8 h: 68% vs 64%), vomiting (1 h: 4% vs 0%, 8 h: 0% vs 4%), or pruritus (1 h: 4% vs 16%, 8 h: 40% vs 40%). There was no difference in the amount of medication required to treat side effects or patient satisfaction. The average ratio of morphine to hydromorphone use was about 7:1. The patients used 10.9+/-6.0 mg morphine versus 1.57+/-1.0 mg hydromorphone after 1 h and 29.0+/-18.0 mg morphine versus 3.9+/-2.5 mg hydromorphone after 8 h. There was no difference between the morphine and hydromorphone groups with respect to postoperative pain scores with movement at 1 h (7.9+/-2.3 vs 7.1+/-2.4) or 8 h (5.7+/-2.8 vs 5.9+/-2.7). There was also no difference in pain at rest or miosis between groups.

CONCLUSIONS

We found no systematic difference between morphine and hydromorphone in opioid-related side effects. Neither was there any difference in efficacy of pain control or patient satisfaction when patients self-titrated to equal drug effect as measured by equianalgesia and pupillary miosis. The choice between morphine and hydromorphone for use in PCA should be guided by patient history, as there may be idiosyncratic reactions to either drug.

Induction effects of ritonavir: implications for drug interactions

OBJECTIVE

To review the literature on the induction effects of ritonavir on the cytochrome P450 enzyme system and glucuronyl transferase and identify resultant established and potential drug interactions.

DATA SOURCES

Primary literature was identified from MEDLINE (1950-April 2008), EMBASE (1988-April 2008) and International Pharmaceutical Abstracts (1970-April 2008) using the search terms ritonavir, cytochrome P450 enzyme system, enzyme induction, glucuronyl transferase, and drug interactions. Additionally, relevant conference abstracts and references of relevant articles were reviewed.

STUDY SELECTION AND DATA ABSTRACTION

All English-language articles and abstracts identified were reviewed.

DATA SYNTHESIS

Ritonavir is a well-known inhibitor of the metabolism of numerous medications that are substrates of the CYP3A and CYP2D6 pathways. It also exhibits a biphasic, time-dependent effect on P-glycoprotein of inhibition followed by induction. Numerous pharmacokinetic studies suggested that ritonavir induces cytochrome P450 enzymes 3A, 1A2, 2B6, 2C9, and 2C19, as well as glucuronyl transferase. Additionally, several case reports described clinically significant subtherapeutic effects of drugs metabolized by these isoenzymes when coadministered with ritonavir. Both therapeutic and boosting doses of ritonavir appear to induce these enzymes; however, most of the studies of low-dose ritonavir involved a second protease inhibitor such as lopinavir, darunavir, or tipranavir. It is, therefore, difficult to distinguish the relative effects of additional medications unless well-designed, 3-way studies are conducted.

CONCLUSIONS

At both therapeutic and boosting doses, ritonavir exhibits a clinically relevant induction effect on numerous drug-metabolizing enzymes. A decrease or loss of therapeutic effect may be observed when ritonavir is coadministered with medications that are substrates for these enzymes. It is important for clinicians to be aware of drugs potentially impacted by ritonavir therapy to identify and manage these interactions.

Complicated pain management in a CYP450 2D6 poor metabolizer

We describe the case of a patient with significant adverse effects from posttraumatic analgesic therapy with opioid analgesics who was found by microarray analysis to have a CYP2D6 genotype predictive of a poor metabolizer phenotype. In addition to her poor tolerance and limited response to opioid analgesics, she developed further discomfort when the antiemetic promethazine was administered to treat her gastrointestinal adverse effects. In our discussion we review the literature about the clinical impact of CYP450 2D6 polymorphisms in treatment with the commonly used opioid analgesics codeine, oxycodone, hydrocodone, hydromorphone, and morphine, as well as the antiemetic promethazine. The case we present, as well as the literature we review, demonstrates the clinical utility of CYP2D6 genotyping in patients with adverse effects from analgesia therapy.