Impact of the CYP2D6 genotype on post-operative intravenous oxycodone analgesia

Managing Severe Cancer Pain with Oxycodone/Naloxone Treatment: A Literature Review Update

Severe cancer pain substantially affects patients' quality of life, increasing the burden of the disease and reducing the disability-adjusted life years. Although opioid analgesics are effective, they may induce opioid-induced bowel dysfunction (OIBD). Oxycodone/naloxone combination therapy has emerged as a promising approach to mitigate opioid-induced constipation (OIC) while providing effective pain relief. This review provides an updated analysis of the literature of the last decade regarding the use of oxycodone/naloxone in the management of severe cancer pain. Through a comprehensive search of databases, studies focusing on the efficacy, safety, and patient experience of oxycodone/naloxone's prolonged release in severe cancer pain management were identified. Furthermore, the literature discusses the mechanism of action of naloxone in mitigating OIC without compromising opioid analgesia. Overall, the evidence suggests that oxycodone/naloxone combination therapy offers a valuable option for effectively managing severe cancer pain while minimizing opioid-induced constipation, thereby improving patients' quality of life. However, further research is needed to optimize dosing regimens, evaluate long-term safety, and assess patient outcomes in diverse cancer populations.

Pharmacogenetic Approaches in Personalized Medicine for Postoperative Pain Management

Despite technical and pharmacological advancements in recent years, including optimized therapies and personalized medicine, postoperative pain management remains challenging and sometimes undertreated. This review aims to summarize and update how genotype-guided therapeutics within personalized medicine can enhance postoperative pain management. Several studies in the area have demonstrated that genotype-guided therapy has the ability to lower opioid consumption and improve postoperative pain. Gene mutations, primarily OPRM1, CYP2D6, CYP2C9, COMT and ABCB1, have been shown to exert nuanced influences on analgesic response and related pharmacological outcomes. This review underscores the integration of pharmacogenetic-guided personalized medicine into perioperative care, particularly when there is uncertainty regarding opioid prescriptions. This approach leads to superior outcomes in terms of postoperative pain relief and reduced morbidity for numerous patients.

CYP2D6-guided opioid therapy for adults with cancer pain: A randomized implementation clinical trial

INTRODUCTION

The CYP2D6 enzyme metabolizes opioids commonly prescribed for cancer-related pain, and CYP2D6 polymorphisms may contribute to variability in opioid response. We evaluated the feasibility of implementing CYP2D6-guided opioid prescribing for patients with cancer and reported pilot outcome data.

METHODS

Adult patients from two cancer centers were prospectively enrolled into a hybrid implementation-effectiveness clinical trial and randomized to CYP2D6-genotype-guided opioid selection, with clinical recommendations, or usual care. Implementation metrics, including provider response, medication changes consistent with recommendations, and patient-reported pain and symptom scores at baseline and up to 8 weeks, were assessed.

RESULTS

Most (87/114, 76%) patients approached for the study agreed to participate. Of 85 patients randomized, 71% were prescribed oxycodone at baseline. The median (range) time to receive CYP2D6 test results was 10 (3-37) days; 24% of patients had physicians acknowledge genotype results in a clinic note. Among patients with CYP2D6-genotype-guided recommendations to change therapy (n = 11), 18% had a change congruent with recommendations. Among patients who completed baseline and follow-up questionnaires (n = 48), there was no difference in change in mean composite pain score (-1.01 ± 2.1 vs. -0.41 ± 2.5; p = 0.19) or symptom severity at last follow-up (3.96 ± 2.18 vs. 3.47 ± 1.78; p = 0.63) between the usual care arm (n = 26) and genotype-guided arm (n = 22), respectively.

CONCLUSION

Our study revealed high acceptance of pharmacogenetic testing as part of a clinical trial among patients with cancer pain. However, provider response to genotype-guided recommendations was low, impacting assessment of pain-related outcomes. Addressing barriers to utility of pharmacogenetics results and clinical recommendations will be critical for implementation success.

Pharmacogenetic Analysis Enables Optimization of Pain Therapy: A Case Report of Ineffective Oxycodone Therapy

Patients suffering from chronic pain may respond differently to analgesic medications. For some, pain relief is insufficient, while others experience side effects. Although pharmacogenetic testing is rarely performed in the context of analgesics, response to opiates, non-opioid analgesics, and antidepressants for the treatment of neuropathic pain can be affected by genetic variants. We describe a female patient who suffered from a complex chronic pain syndrome due to a disc hernia. Due to insufficient response to oxycodone, fentanyl, and morphine in addition to non-steroidal anti-inflammatory drug (NSAID)-induced side effects reported in the past, we performed panel-based pharmacogenotyping and compiled a medication recommendation. The ineffectiveness of opiates could be explained by a combined effect of the decreased activity in cytochrome P450 2D6 (CYP2D6), an increased activity in CYP3A, and an impaired drug response at the µ-opioid receptor. Decreased activity for CYP2C9 led to a slowed metabolism of ibuprofen and thus increased the risk for gastrointestinal side effects. Based on these findings we recommended hydromorphone and paracetamol, of which the metabolism was not affected by genetic variants. Our case report illustrates that an in-depth medication review including pharmacogenetic analysis can be helpful for patients with complex pain syndrome. Our approach highlights how genetic information could be applied to analyze a patient's history of medication ineffectiveness or poor tolerability and help to find better treatment options.

Effects of oxycodone pharmacogenetics on postoperative analgesia and related clinical outcomes in children: a pilot prospective study

Background: Variability in the pharmacokinetics and pharmacodynamics of oxycodone in children undergoing surgery could be due to genetic polymorphisms. Materials & methods: The authors studied the association between clinical outcomes and pharmacogenes in children undergoing major surgery. A total of 89 children (35 undergoing pectus excavatum repair and 54 undergoing spinal fusion) were recruited. Results: OPRM1 SNP rs6902403 showed an association with maximum pain score and total morphine equivalent dose (p < 0.05). Other polymorphisms in OPRM1 SNP, PXR, COMT and ABCB1 were also shown to be associated with average morphine equivalent dose, length of hospital stay and maximum surgical pain (p < 0.05). Conclusion: This study demonstrates novel associations between the above pharmacogenes and oxycodone's pharmacokinetics as well as postoperative outcomes in children. Clinical trial registration: NCT03495388 (ClinicalTrials.gov).

Implementing a pragmatic clinical trial to tailor opioids for acute pain on behalf of the IGNITE ADOPT PGx investigators

Opioid prescribing for postoperative pain management is challenging because of inter-patient variability in opioid response and concern about opioid addiction. Tramadol, hydrocodone, and codeine depend on the cytochrome P450 2D6 (CYP2D6) enzyme for formation of highly potent metabolites. Individuals with reduced or absent CYP2D6 activity (i.e., intermediate metabolizers [IMs] or poor metabolizers [PMs], respectively) have lower concentrations of potent opioid metabolites and potentially inadequate pain control. The primary objective of this prospective, multicenter, randomized pragmatic trial is to determine the effect of postoperative CYP2D6-guided opioid prescribing on pain control and opioid usage. Up to 2020 participants, age ≥8 years, scheduled to undergo a surgical procedure will be enrolled and randomized to immediate pharmacogenetic testing with clinical decision support (CDS) for CYP2D6 phenotype-guided postoperative pain management (intervention arm) or delayed testing without CDS (control arm). CDS is provided through medical record alerts and/or a pharmacist consult note. For IMs and PM in the intervention arm, CDS includes recommendations to avoid hydrocodone, tramadol, and codeine. Patient-reported pain-related outcomes are collected 10 days and 1, 3, and 6 months after surgery. The primary outcome, a composite of pain intensity and opioid usage at 10 days postsurgery, will be compared in the subgroup of IMs and PMs in the intervention (n = 152) versus the control (n = 152) arm. Secondary end points include prescription pain medication misuse scores and opioid persistence at 6 months. This trial will provide data on the clinical utility of CYP2D6 phenotype-guided opioid selection for improving postoperative pain control and reducing opioid-related risks.

Dutch Pharmacogenetics Working Group (DPWG) guideline for the gene-drug interaction between CYP2D6 and opioids (codeine, tramadol and oxycodone)

The current Dutch Pharmacogenetics Working Group (DPWG) guideline, describes the gene-drug interaction between CYP2D6 and the opioids codeine, tramadol and oxycodone. CYP2D6 genotype is translated into normal metaboliser (NM), intermediate metaboliser (IM), poor metaboliser (PM) or ultra-rapid metaboliser (UM). Codeine is contraindicated in UM adults if doses >20 mg every 6 h (q6h), in children ≥12 years if doses >10 mg q6h, or with additional risk factors. In PMs, an alternative analgesic should be given which is not or to a lesser extent metabolised by CYP2D6 (not tramadol). In IMs with insufficient analgesia, a higher dose or alternative analgesic should be given. For tramadol, the recommendations for IMs and PMs are the same as the recommendation for codeine and IMs. UMs should receive an alternative drug not or to a lesser extent metabolised by CYP2D6 or the dose should be decreased to 40% of the commonly prescribed dose. Due to the absence of effect on clinical outcomes of oxycodone in PMs, IMs and UMs no action is required. DPWG classifies CYP2D6 genotyping for codeine "beneficial" and recommends testing prior to, or shortly after initiation of treatment in case of higher doses or additional risk factors. CYP2D6 genotyping is classified as "potentially beneficial" for tramadol and can be considered on an individual patient basis.

Zhx2 Is a Candidate Gene Underlying Oxymorphone Metabolite Brain Concentration Associated with State-Dependent Oxycodone Reward

Understanding the pharmacogenomics of opioid metabolism and behavior is vital to therapeutic success, as mutations can dramatically alter therapeutic efficacy and addiction liability. We found robust, sex-dependent BALB/c substrain differences in oxycodone behaviors and whole brain concentration of oxycodone metabolites. BALB/cJ females showed robust state-dependent oxycodone reward learning as measured via conditioned place preference when compared with the closely related BALB/cByJ substrain. Accordingly, BALB/cJ females also showed a robust increase in brain concentration of the inactive metabolite noroxycodone and the active metabolite oxymorphone compared with BALB/cByJ mice. Oxymorphone is a highly potent, full agonist at the mu opioid receptor that could enhance drug-induced interoception and state-dependent oxycodone reward learning. Quantitative trait locus (QTL) mapping in a BALB/c F2 reduced complexity cross revealed one major QTL on chromosome 15 underlying brain oxymorphone concentration that explained 32% of the female variance. BALB/cJ and BALB/cByJ differ by fewer than 10,000 variants, which can greatly facilitate candidate gene/variant identification. Hippocampal and striatal cis-expression QTL (eQTL) and exon-level eQTL analysis identified Zhx2, a candidate gene coding for a transcriptional repressor with a private BALB/cJ retroviral insertion that reduces Zhx2 expression and sex-dependent dysregulation of cytochrome P450 enzymes. Whole brain proteomics corroborated the Zhx2 eQTL and identified upregulated CYP2D11 that could increase brain oxymorphone in BALB/cJ females. To summarize, Zhx2 is a highly promising candidate gene underlying brain oxycodone metabolite levels. Future studies will validate Zhx2 and its site of action using reciprocal gene editing and tissue-specific viral manipulations in BALB/c substrains. SIGNIFICANCE STATEMENT: Our findings show that genetic variation can result in sex-specific alterations in whole brain concentration of a bioactive opioid metabolite after oxycodone administration, reinforcing the need for sex as a biological factor in pharmacogenomic studies. The cooccurrence of female-specific increased oxymorphone and state-dependent reward learning suggests that this minor yet potent and efficacious metabolite of oxycodone could increase opioid interoception and drug-cue associative learning of opioid reward, which has implications for cue-induced relapse of drug-seeking behavior and for precision pharmacogenetics.

Sex, estrous cycle, and hormone regulation of CYP2D in the brain alters oxycodone metabolism and analgesia

Opioids, and numerous centrally active drugs, are metabolized by cytochrome P450 2D (CYP2D). There are sex and estrous cycle differences in brain oxycodone analgesia. Here we investigated the mechanism examining the selective role of CYP2D in the brain on sex, estrous cycle, and hormonal regulation. Propranolol, CYP2D-specific mechanism-based inhibitor, or vehicle was delivered into cerebral ventricles 24 hours before administering oxycodone (or oxymorphone, negative control) orally to male and female (in estrus and diestrus) rats. Ovariectomized and sham-operated females received no treatment, estradiol, progesterone or vehicle. Analgesia was measured using tail-flick latency, and brain drug and metabolite concentrations were measured by microdialysis. Data were analyzed by two-way or mixed ANOVA. Following propranolol (versus vehicle) inhibition and oral oxycodone, there were greater increases in brain oxycodone concentrations and analgesia, and greater decreases in brain oxymorphone/oxycodone ratios (an in vivo phenotype of CYP2D in brain) in males and females in estrus, compared to females in diestrus; with no impact on plasma drug concentrations. There was no impact of propranolol pre-treatment, sex, or cycle after oral oxymorphone (non-CYP2D substrate) on brain oxymorphone concentrations or analgesia. There was no impact of propranolol pre-treatment following ovariectomy on brain oxycodone concentrations or analgesia, which was restored in ovariectomized females following estradiol, but not progesterone, treatment. Sex, cycle, and estradiol regulation of CYP2D in brain in turn altered brain oxycodone concentration and response, which may contribute to the large inter-individual variation in response to the numerous centrally acting CYP2D substrate drugs, including opioids.

Pharmacogenetics: A Precision Medicine Approach to Combatting the Opioid Epidemic

Ineffective pain control is the most commonly cited reason for misuse of prescription opioids and is influenced by genetics. In particular, the gene encoding the CYP2D6 enzyme, which metabolizes some of the most commonly prescribed opioids (e.g., tramadol, hydrocodone) to their more potent forms, is highly polymorphic and can lead to reduced concentrations of the active metabolites and decreased opioid effectiveness. Consideration of the CYP2D6 genotype may allow for predicting opioid response and identifying patients who are likely to respond well to lower potency opioids as well as those who may derive greater pain relief from non-opioid analgesics versus certain opioids. There is emerging evidence that a CYP2D6-guided approach to pain management improves pain control and reduces opioid consumption and thus may be a promising means for combating opioid misuse. Clinical practice guidelines are available for select opioids and other analgesics to support medication and dose selection based on pharmacogenetic data. This article describes the evidence supporting genotype-guided pain management as a means of improving pain control and reducing opioid misuse and clinical recommendations for genotype-guided analgesic prescribing. In addition, a "how to" guide using patient case examples is provided to demystify the process for implementing pharmacogenetics-guided pain management in order to optimize analgesia and minimize adverse effects. Optimizing pain management through genotype-guided approaches may ultimately provide safer and more effective therapy for pain control while decreasing the risk for opioid misuse.

Pharmacogenomics of Opioid Treatment for Pain Management

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

Appraisal and development of evidence-based clinical decision support to enable perioperative pharmacogenomic application

Variable responses to medications complicates perioperative care. As a potential solution, we evaluated and synthesized pharmacogenomic evidence that may inform anesthesia and pain prescribing to identify clinically actionable drug/gene pairs. Clinical decision-support (CDS) summaries were developed and were evaluated using Appraisal of Guidelines for Research and Evaluation (AGREE) II. We found that 93/180 (51%) of commonly-used perioperative medications had some published pharmacogenomic information, with 18 having actionable evidence: celecoxib/diclofenac/flurbiprofen/ibuprofen/piroxicam/CYP2C9, codeine/oxycodone/tramadol CYP2D6, desflurane/enflurane/halothane/isoflurane/sevoflurane/succinylcholine/RYR1/CACNA1S, diazepam/CYP2C19, phenytoin/CYP2C9, succinylcholine/mivacurium/BCHE, and morphine/OPRM1. Novel CDS summaries were developed for these 18 medications. AGREE II mean ± standard deviation scores were high for Scope and Purpose (95.0 ± 2.8), Rigor of Development (93.2 ± 2.8), Clarity of Presentation (87.3 ± 3.0), and Applicability (86.5 ± 3.7) (maximum score = 100). Overall mean guideline quality score was 6.7 ± 0.2 (maximum score = 7). All summaries were recommended for clinical implementation. A critical mass of pharmacogenomic evidence exists for select medications commonly used in the perioperative setting, warranting prospective examination for clinical utility.

Reviewing pharmacogenetics to advance precision medicine for opioids

BACKGROUND

Adequate opioid prescribing is critical for therapeutic success of pain management. Despite the widespread use of opioids, optimized opioid therapy remains unresolved with risk of accidental lethal overdosing. With the emergence of accumulating evidence linking genetic variation to opioid response, pharmacogenetic based treatment recommendations have been proposed.

OBJECTIVE

The aim of this review is to evaluate pharmacogenetic evidence and provide an overview on genes involved in the pharmacokinetics and pharmacodynamics of opioids.

METHODS

For this review, a systematic literature search of published articles was used in PubMed®, with no language restriction and between the time period of January 2000 to December 2020. We reviewed randomized clinical studies, study cohorts and case reports that investigated the influence of genetic variants on selected opioid pharmacokinetics and pharmacodynamics. In addition, we reviewed current CPIC clinical recommendations for pharmacogenetic testing.

RESULTS

Results of this review indicate consistent evidence supporting the association between selected genetic variants of CYP2D6 for opioid metabolism. CPIC guidelines include recommendations that indicate the avoidance of tramadol use, in addition to codeine, in CYP2D6 poor metabolizers and ultrarapid metabolizers, and to monitor intermediate metabolizers for less-than-optimal response. While there is consistent evidence for OPRM1 suggesting increased postoperative morphine dosing requirements in A118G G-allele carriers, the clinical relevance remains limited.

CONCLUSION

There is emerging evidence of clinical relevance of CYP2D6 and, to a lesser extent, OPRM1 polymorphism in personalized opioid drug dosing. As a result, first clinics have started to implement pharmacogenetic guidelines for CYP2D6 and codeine.

Contribution of CYP2D6 Functional Activity to Oxycodone Efficacy in Pain Management: Genetic Polymorphisms, Phenoconversion, and Tissue-Selective Metabolism

Oxycodone is a widely used opioid for the management of chronic pain. Analgesic effects observed following the administration of oxycodone are mediated mostly by agonistic effects on the μ-opioid receptor. Wide inter-subject variability observed in oxycodone efficacy could be explained by polymorphisms in the gene coding for the μ-opioid receptor (OPRM1). In humans, oxycodone is converted into several metabolites, particularly into oxymorphone, an active metabolite with potent μ-opioid receptor agonist activity. The CYP2D6 enzyme is principally responsible for the conversion of oxycodone to oxymorphone. The CYP2D6 gene is highly polymorphic with encoded protein activities, ranging from non-functioning to high-functioning enzymes. Several pharmacogenetic studies have shown the importance of CYP2D6-mediated conversion of oxycodone to oxymorphone for analgesic efficacy. Pharmacogenetic testing could optimize oxycodone therapy and help achieve adequate pain control, avoiding harmful side effects. However, the most recent Clinical Pharmacogenetics Implementation Consortium guidelines fell short of recommending pharmacogenomic testing for oxycodone treatment. In this review, we (1) analyze pharmacogenomic and drug-interaction studies to delineate the association between CYP2D6 activity and oxycodone efficacy, (2) review evidence from CYP3A4 drug-interaction studies to untangle the nature of oxycodone metabolism and its efficacy, (3) report on the current knowledge linking the efficacy of oxycodone to OPRM1 variants, and (4) discuss the potential role of CYP2D6 brain expression on the local formation of oxymorphone. In conclusion, we opine that pharmacogenetic testing, especially for CYP2D6 with considerations of phenoconversion due to concomitant drug administration, should be appraised to improve oxycodone efficacy.

Impact of CYP2D6 Pharmacogenomic Status on Pain Control Among Opioid-Treated Oncology Patients

BACKGROUND

Several opioids have pharmacogenomic associations impacting analgesic efficacy. However, germline pharmacogenomic testing is not routinely incorporated into supportive oncology. We hypothesized that CYP2D6 profiling would correlate with opioid prescribing and hospitalizations.

MATERIALS AND METHODS

We analyzed 61,572 adult oncology patients from 2012 to 2018 for opioid exposures. CYP2D6 metabolizer phenotype (ultra-rapid [UM], normal metabolizer [NM], intermediate [IM], or poor [PM]), the latter two of which may cause inefficacy of codeine, tramadol, and standard-dose hydrocodone, was determined for patients genotyped for reasons unrelated to pain. The primary endpoint was number of opioid medications received during longitudinal care (IM/PMs vs. NMs). Secondary endpoint was likelihood of pain-related hospital encounters.

RESULTS

Most patients with cancer (n = 34,675, 56%) received multiple opioids (average 2.8 ± 1.6/patient). Hydrocodone was most commonly prescribed (62%), followed by tramadol, oxycodone, and codeine. In the CYP2D6 genotyped cohort (n = 105), IM/PMs received a similar number of opioids (3.4 ± 1.4) as NMs (3.3 ± 1.9). However, IM/PMs were significantly more likely to experience pain-related hospital encounters compared with NMs, independent of other variables (odds ratio [OR] = 5.4; 95% confidence interval [CI], 1.2-23.6; p = .03). IM/PMs were also more likely to be treated with later-line opioids that do not require CYP2D6 metabolism, such as morphine and hydromorphone (OR = 3.3; 95% CI, 1.1-9.8; p = .03).

CONCLUSION

CYP2D6 genotype may identify patients with cancer at increased risk for inadequate analgesia when treated with typical first-line opioids like codeine, tramadol, or standard-dose hydrocodone. Palliative care considerations are an integral part of optimal oncology care, and these findings justify prospective evaluation of preemptive genotyping as a strategy to improve oncology pain management.

IMPLICATIONS FOR PRACTICE

Genomic variation in metabolic enzymes can predispose individuals to inefficacy when receiving opioid pain medications. Patients with intermediate and/or poor CYP2D6 metabolizer status do not adequately convert codeine, tramadol, and hydrocodone into active compounds, with resulting increased risk of inadequate analgesia. This study showed that patients with cancer frequently receive CYP2D6-dependent opioids. However, patients with CYP2D6 intermediate and poor metabolizer status had increased numbers of pain-related hospitalizations and more frequently required the potent non-CYP2D6 opioids morphine and hydromorphone. This may reflect inadequate initial analgesia with the common "first-line" CYP2D6-metabolized opioids. Preemptive genotyping to guide opioid prescribing during cancer care may improve pain-related patient outcomes.

Oxycodone findings and CYP2D6 function in postmortem cases

Genetic disposition can cause variation in oxycodone pharmacokinetic characteristics and decrease or increase the expected clinical response. In forensic medicine, determination of cause of death or assessing time between drug intake and death can be facilitated by knowledge of parent and metabolite concentrations. In this study, the aim was to investigate if CYP2D6 genotyping can facilitate interpretation by investigating the frequency of the four CYP2D6 phenotypes, poor metabolizer, intermediate metabolizer, extensive metabolizer, and ultra-rapid metabolizer in postmortem cases, and to study if the CYP2D6 activity was associated with a certain cause of death, concentration, or metabolic ratio. Cases positive for oxycodone in femoral blood (n = 174) were genotyped by pyrosequencing for CYP2D6*3, *4, and *6 and concentrations of oxycodone, noroxycodone, oxymorphone, and noroxymorphone were determined by LC-MS/MS (LLOQ 0.005 µg/g). Digital droplet PCR was used to determine the copy number variation for CYP2D6*5. Cases were categorized by cause of death. It was found that poor and intermediate CYP2D6 metabolizers had significantly higher oxycodone and noroxycodone concentrations compared to extensive and ultra-rapid metabolizers. CYP2D6 phenotype were equally distributed between cause of death groups, showing that no phenotype was overrepresented in any of the cause of death groups. We also found that the concentration ratio between oxymorphone and oxycodone depended on the CYP2D6 activity when death was unrelated to intoxication. In general, a low metabolite to parent ratio indicate an acute intake. By using receiver operating characteristic (ROC) analysis, we conclude that an oxymorphone/oxycodone ratio lower than 0.075 has a high sensitivity for separating intoxications with oxycodone from other intoxications and non-intoxications. However, the phenotype needs to be known to reach a high specificity. Therefore, the ratio should not be used as a biomarker on its own to distinguish between different causes of death but needs to be complemented by genotyping.

Pharmacogenomics of oxycodone: a narrative literature review

Oxycodone is a semisynthetic μ- and κ-opioid receptor with agonist with a broad scope of use including postoperative analgesia as well as control of neuropathic and cancer pain. Advantages over other opioids include prolonged duration of action, greater potency than morphine and lack of histamine release or ceiling effect. Individual responses to oxycodone can vary due to genetic differences. This review article aims to summarize the oxycodone literature and provide context on its pharmacogenomics and pharmacokinetics. The evidence for clinical effect of genetic polymorphisms on oxycodone is conflicting. There is stronger evidence linking polymorphic genetic enzymes CYP2D6 and CYP3A with therapeutic outcomes. Further, research is needed to discern all of oxycodone's metabolites and their contribution to the overall analgesic effect.

Clinical Pharmacogenetics Implementation Consortium Guideline for CYP2D6, OPRM1, and COMT Genotypes and Select Opioid Therapy

Opioids are mainly used to treat both acute and chronic pain. Several opioids are metabolized to some extent by CYP2D6 (codeine, tramadol, hydrocodone, oxycodone, and methadone). Polymorphisms in CYP2D6 have been studied for an association with the clinical effect and safety of these drugs. Other genes that have been studied for their association with opioid clinical effect or adverse events include OPRM1 (mu receptor) and COMT (catechol-O-methyltransferase). This guideline updates and expands the 2014 Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 genotype and codeine therapy and includes a summation of the evidence describing the impact of CYP2D6, OPRM1, and COMT on opioid analgesia and adverse events. We provide therapeutic recommendations for the use of CYP2D6 genotype results for prescribing codeine and tramadol and describe the limited and/or weak data for CYP2D6 and hydrocodone, oxycodone, and methadone, and for OPRM1 and COMT for clinical use.

Pharmacogenomics, concepts for the future of perioperative medicine and pain management: A review

Pharmacogenomics is the study of how genetic differences between individuals affect pharmacokinetics and pharmacodynamics. These differences are apparent to clinicians when taking into account the wide range of responses to medications given in clinical practice. A review of literature involving pharmacogenomics and pain management was performed. The implementation of preoperative pharmacogenomics will allow us to better care for our patients by delivering personalized, safer medicine. This review describes the current state of pharmacogenomics as it relates to many aspects of clinical practice and how clinicians can use these tools to improve patient outcomes.

Physiologically based pharmacokinetic modelling of oxycodone drug-drug interactions

Oxycodone is an opioid analgesic with several pharmacologically active metabolites and relatively narrow therapeutic index. Cytochrome P450 (CYP) 3A4 and CYP2D6 play major roles in the metabolism of oxycodone and its metabolites. Thus, inhibition and induction of these enzymes may result in substantial changes in the exposure of both oxycodone and its metabolites. In this study, a physiologically based pharmacokinetic (PBPK) model was built using GastroPlus™ software for oxycodone, two primary metabolites (noroxycodone, oxymorphone) and one secondary metabolite (noroxymorphone). The model was built based on literature and in house in vitro and in silico data. The model was refined and verified against literature clinical data after oxycodone administration in the absence of drug-drug interactions (DDI). The model was further challenged with simulations of oxycodone DDI with CYP3A4 inhibitors ketoconazole and itraconazole, CYP3A4 inducer rifampicin and CYP2D6 inhibitor quinidine. The magnitude of DDI (AUC ratio) was predicted within 1.5-fold error for oxycodone, within 1.8-fold and 1.3-4.5-fold error for the primary metabolites noroxycodone and oxymorphone, respectively, and within 1.4-4.5-fold error for the secondary metabolite noroxymorphone, when compared to the mean observed AUC ratios. This work demonstrated the capability of PBPK model to simulate DDI of the administered compounds and the formed metabolites of both DDI victim and perpetrator. However, the predictions for the formed metabolites tend to be associated with higher uncertainty than the predictions for the administered compound. The oxycodone model provides a tool for forecasting oxycodone DDI with other CYP3A4 and CYP2D6 DDI perpetrators that may be co-administered with oxycodone.

Pharmacokinetics and Bioequivalence Evaluation of a New Oxycodone Tamper-Resistant Tablet Administered with an Opioid Antagonist in Patients with Chronic Pain

BACKGROUND AND OBJECTIVES

Oxycodone tamper resistant (OTR) is a new extended-release abuse-deterrent formulation providing improvements in the tamper resistant characteristics. This study aimed to investigate the pharmacokinetic properties of the new OTR tablets and evaluate the bioequivalence of oxycodone from OTR and the original extended release (ER) formulation tablets administered with an opioid antagonist in patients with chronic pain.

METHODS

In this open-label, randomized, cross-over study, the enrolled patients were randomised to receive a single dose of 40 mg OTR or 40 mg OXYCONTIN^® (OXY) tablet administered with naltrexone blockade under fasting conditions. Serial blood samples for pharmacokinetic analysis were collected. Plasma oxycodone was quantified by a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. Tolerability was evaluated by monitoring adverse events, physical examinations, 12-lead ECG and laboratory tests.

RESULTS

A total of 38 patients were enrolled and 33 subjects completed the study. After a single dose of 40 mg tablets, pharmacokinetic results of the new OTR tablet were found to be similar to those of original extended-release oxycodone tablet. OTR 40 mg was bioequivalent to OXY 40 mg and was well tolerated in patients with chronic pain.

CONCLUSIONS

The new OTR formulation could provide a new choice in the treatment of chronic pain and reduce the potential for oxycodone abuse. Chictr.org identifier: ChiCTR1800017253.

Update on the pharmacogenomics of pain management

Pharmacogenomics is the study of genetic variants that impact drug effects through changes in a drug’s pharmacokinetics and pharmacodynamics. Pharmacogenomics is being integrated into clinical pain management practice because variants in individual genes can be predictive of how a patient may respond to a drug treatment. Pain is subjective and is considered challenging to treat. Furthermore, pain patients do not respond to treatments in the same way, which makes it hard to issue a consistent treatment regimen for all pain conditions. Pharmacogenomics would bring consistency to the subjective nature of pain and could revolutionize the field of pain management by providing personalized medical care tailored to each patient based on their gene variants. Additionally, pharmacogenomics offers a solution to the opioid crisis by identifying potentially opioid-vulnerable patients who could be recommended a nonopioid treatment for their pain condition. The integration of pharmacogenomics into clinical practice creates better and safer healthcare practices for patients. In this article, we provide a comprehensive history of pharmacogenomics and pain management, and focus on up to date information on the pharmacogenomics of pain management, describing genes involved in pain, genes that may reduce or guard against pain and discuss specific pain management drugs and their genetic correlations.

CYP2D6-guided opioid therapy improves pain control in CYP2D6 intermediate and poor metabolizers: a pragmatic clinical trial

PURPOSE

CYP2D6 bioactivates codeine and tramadol, with intermediate and poor metabolizers (IMs and PMs) expected to have impaired analgesia. This pragmatic proof-of-concept trial tested the effects of CYP2D6-guided opioid prescribing on pain control.

METHODS

Participants with chronic pain (94% on an opioid) from seven clinics were enrolled into CYP2D6-guided (n = 235) or usual care (n = 135) arms using a cluster design. CYP2D6 phenotypes were assigned based on genotype and CYP2D6 inhibitor use, with recommendations for opioid prescribing made in the CYP2D6-guided arm. Pain was assessed at baseline and 3 months using PROMIS^® measures.

RESULTS

On stepwise multiple linear regression, the primary outcome of composite pain intensity (composite of current pain and worst and average pain in the past week) among IM/PMs initially prescribed tramadol/codeine (n = 45) had greater improvement in the CYP2D6-guided versus usual care arm (-1.01 ± 1.59 vs. -0.40 ± 1.20; adj P = 0.016); 24% of CYP2D6-guided versus 0% of usual care participants reported ≥30% (clinically meaningful) reduction in the composite outcome. In contrast, among normal metabolizers prescribed tramadol or codeine at baseline, there was no difference in the change in composite pain intensity at 3 months between CYP2D6-guided (-0.61 ± 1.39) and usual care (-0.54 ± 1.69) groups (adj P = 0.540).

CONCLUSION

These data support the potential benefits of CYP2D6-guided pain management.

Effects of Single Nucleotide Polymorphisms on Surgical and Postsurgical Opioid Requirements: A Systematic Review and Meta-Analysis

OBJECTIVES

There is great heterogeneity in the way individuals respond to medications. Inherited differences, such as single nucleotide polymorphisms (SNP), can influence the efficacy and toxicity of drugs. This meta-analysis aims to collate data from studies investigating the effect of SNPs on postoperative and/or intraoperative opioid requirements.

MATERIALS AND METHODS

A meta-analysis was conducted following PRISMA guidelines. Eligibility criteria for studies included were reporting amount of postoperative and/or intraoperative opioid used as the primary outcome and genotyping patients for SNPs in one of the following genes; OPRM1, CYP2D6, CYP3A4, CYP3A5, COMT, UGT2B7, or ABCB1. A comprehensive systematic search for articles using keywords "opioid-sensitivity," "polymorphisms," "post-operative opioid," "post-surgical opioid," "post-operative pain," and "post-surgical pain" was performed.

RESULTS

Fifty-one studies were included. Individuals homozygous for AA at the OPRMI (rs1799971) polymorphisms required less postsurgical opioid compared with those homozygous for GG (Hedges g, -0.270; 95% confidence interval, -0.433 to -0.108; P=0.001). Polymorphisms in CYP2D6, CYP3A4, CYP3A5, COMT, UGT2B7, and ABCB1 did not affect opioid requirements.

DISCUSSION

Investigation of single changes in 1 gene can only yield limited information regarding genetic effects on opioid requirements. Rapid development of whole genome sequencing enables information on all genetic modifications that may affect analgesic response to be collected. The information collected must include data on the individual's metabolic enzymes, as well as information on drug receptors and enzymes responsible for drug degradation, so that a personal profile can be built up which will predict individual response to drugs, and guide clinicians on the type and dosage of drug to use.

Design and rational for the precision medicine guided treatment for cancer pain pragmatic clinical trial

INTRODUCTION

Pain is one of the most burdensome symptoms associated with cancer and its treatment, and opioids are the cornerstone of pain management. Opioid therapy is empirically selected, and patients often require adjustments in therapy to effectively alleviate pain or ameliorate adverse drug effects that interfere with quality of life. There are data suggesting CYP2D6 genotype may contribute to inter-patient variability in response to opioids through its effects on opioid metabolism. Therefore, we aim to determine if CYP2D6 genotype-guided opioid prescribing results in greater reductions in pain and symptom severity and interference with daily living compared to a conventional prescribing approach in patients with cancer.

METHODS

Patients with solid tumors with metastasis and a self-reported pain score ≥ 4/10 are eligible for enrollment and randomized to a genotype-guided or conventional pain management strategy. For patients in the genotype-guided arm, CYP2D6 genotype information is integrated into opioid prescribing decisions. Patients are asked to complete questionnaires regarding their pain, symptoms, and quality of life at baseline and 2, 4, 6, and 8 weeks after enrollment. The primary endpoint is differential change in pain severity by treatment strategy (genotype-guided versus conventional pain management). Secondary endpoints include change in pain and symptom interference with daily living.

CONCLUSION

Pharmacogenetic-guided opioid selection for cancer pain management has potential clinical utility, but current evidence is limited to retrospective and observational studies. Precision Medicine Guided Treatment for Cancer Pain is a pragmatic clinical trial that seeks to determine the utility of CYP2D6 genotype-guided opioid prescribing in patients with cancer.

Codeine and opioid metabolism: implications and alternatives for pediatric pain management

PURPOSE OF REVIEW

Use of perioperative opioids for surgical pain management of children presents clinical challenges because of concerns of serious adverse effects including life-threatening respiratory depression. This is especially true for children with history of obstructive sleep apnea. This review will explore current knowledge of clinically relevant factors and genetic polymorphisms that affect opioid metabolism and postoperative outcomes in children.

RECENT FINDINGS

Within the past several years, an increasing number of case reports have illustrated clinically important respiratory depression, anoxic brain injuries and even death among children receiving appropriate weight-based dosages of codeine and other opioids for analgesia at home setting particularly following tonsillectomy. Several national and international organizations have issued advisories on use of codeine in pediatrics, based on cytochrome P450 family 2 subfamily D type 6 (CYP2D6) pharmacogenetics. We have discussed the pros and cons of alternatives to codeine for pain management.

SUMMARY

Although routine preoperative genotyping to identify children at risk and personalized opioid use for pediatric perioperative pain management is still a distant reality, current known implications of CYP2D6 pharmacogenetics on codeine use shows that pharmacogenetics has the potential to guide anesthesia providers on perioperative opioid selection and dosing to maximize efficacy and safety.

Pharmacogenetics of Opioid Use and Implications for Pain Management

BACKGROUND

Opioid analgesics are frequently prescribed to manage acute and chronic pain, but individual differences in opioid response make effective pain control in all patients an elusive goal. Furthermore, the risk of addiction following opioid consumption varies among individual patients. Although many psychosocial factors contribute to an individual's opioid response and risk for addiction, a strong genetic component has also been demonstrated.

CONTENT

Opioids undergo substantial enzymatic modification that can generate metabolites with either increased or decreased opioid activity relative to the parent compound. To elicit their analgesic effect, parent compounds and active metabolites must be transported into the central nervous system where they bind to opioid receptors and inhibit neurotransmission. Inherited genetic variants that alter the function of proteins involved in these processes have been associated with differences in opioid response and risk for addiction. Detection of these variants can help guide opioid selection, inform dosing decisions, or encourage use of a nonopioid analgesic.

SUMMARY

Whereas some genetic variants are clearly associated with differences in opioid response and have been included in consensus clinical practice guidelines, the impact of other variants on opioid response remains unclear. Studies performed to date have generated promising results, but inconsistent findings, reimbursement challenges, and the lack of robust decision support tools have hampered widespread adoption of pharmacogenetic testing to guide pain management treatment decisions. Future work involving the simultaneous evaluation of large numbers of variants and demonstration of a clear clinical benefit provided by pharmacogenetic testing will be required to overcome these obstacles.

Analgesic Plasma Concentrations of Oxycodone After Surgery for Breast Cancer-Which Factors Matter?

We investigated factors affecting analgesic oxycodone concentrations after breast cancer surgery in 1,000 women. Preoperatively, we studied heat and cold pain sensitivities and anxiety scores. Postoperatively, rest and motion pain intensities were measured and intravenous oxycodone was administered until satisfactory analgesia. At this point, the mean oxycodone concentration (variation coefficient) was 33.3 ng/mL (66%) and it was 21.7 ng/mL (69%) when the patient requested oxycodone again. At both time points, the concentrations varied >100-fold between individuals. The analgesic oxycodone concentration was increased by 21.3% per motion pain intensity score on a 0-10 scale and by 22.3% if axillary clearance was performed instead of sentinel node biopsy (P < 0.001). Forty-seven women who were older and less anxious than others (P < 0.01) required no oxycodone. Anxiety, age, chronic pain, or preoperative pain sensitivity were not independently associated with the analgesic oxycodone concentration. CYP2D6 and CYP3A genotypes did not affect analgesic concentration or duration of analgesia.

CYP2D6 phenotypes are associated with adverse outcomes related to opioid medications

BACKGROUND

Variation in the CYP2D6 gene may affect response to opioids in both poor and ultrarapid metabolizers, but data demonstrating such associations have been mixed, and the impact of variants on toxicity-related symptoms (e.g., nausea) is unclear. Therefore, we examined the association between CYP2D6 phenotype and poor pain control or other adverse symptoms related to the use of opioids in a sample of primary care patients.

MATERIALS AND METHODS

We identified all patients in the Mayo Clinic RIGHT Protocol who were prescribed an opioid medication between July 01, 2013 and June 30, 2015, and categorized patients into three phenotypes: poor, intermediate to extensive, or ultrarapid CYP2D6 metabolizers. We reviewed the electronic health record of these patients for indications of poor pain control or adverse symptoms related to medication use. Associations between phenotype and outcomes were assessed using Chi-square tests and logistic regression.

RESULTS

Overall, 257 (25% of RIGHT Protocol participants) patients received at least one opioid prescription; of these, 40 (15%) were poor metabolizers, 146 (57%) were intermediate to extensive metabolizers, and 71 (28%) were ultrarapid metabolizers. We removed patients that were prescribed a CYP2D6 inhibitor medication (n=38). After adjusting for age and sex, patients with a poor or ultrarapid phenotype were 2.7 times more likely to experience either poor pain control or an adverse symptom related to the prescription compared to patients with an intermediate to extensive phenotype (odds ratio: 2.68; 95% CI: 1.39, 5.17; p=0.003).

CONCLUSION

Our results suggest that >30% of patients with a poor or ultrarapid CYP2D6 phenotype may experience an adverse outcome after being prescribed codeine, tramadol, oxycodone, or hydrocodone. These medications are frequently prescribed for pain relief, and ~39% of the US population is expected to carry one of these phenotypes, suggesting that the population-level impact of these gene-drug interactions could be substantial.

CYP2D6 phenotypes are associated with adverse outcomes related to opioid medications

Background

Variation in the CYP2D6 gene may affect response to opioids in both poor and ultrarapid metabolizers, but data demonstrating such associations have been mixed, and the impact of variants on toxicity-related symptoms (e.g., nausea) is unclear. Therefore, we examined the association between CYP2D6 phenotype and poor pain control or other adverse symptoms related to the use of opioids in a sample of primary care patients.

Materials and methods

We identified all patients in the Mayo Clinic RIGHT Protocol who were prescribed an opioid medication between July 01, 2013 and June 30, 2015, and categorized patients into three phenotypes: poor, intermediate to extensive, or ultrarapid CYP2D6 metabolizers. We reviewed the electronic health record of these patients for indications of poor pain control or adverse symptoms related to medication use. Associations between phenotype and outcomes were assessed using Chi-square tests and logistic regression.

Results

Overall, 257 (25% of RIGHT Protocol participants) patients received at least one opioid prescription; of these, 40 (15%) were poor metabolizers, 146 (57%) were intermediate to extensive metabolizers, and 71 (28%) were ultrarapid metabolizers. We removed patients that were prescribed a CYP2D6 inhibitor medication (n=38). After adjusting for age and sex, patients with a poor or ultrarapid phenotype were 2.7 times more likely to experience either poor pain control or an adverse symptom related to the prescription compared to patients with an intermediate to extensive phenotype (odds ratio: 2.68; 95% CI: 1.39, 5.17; p=0.003).

Conclusion

Our results suggest that >30% of patients with a poor or ultrarapid CYP2D6 phenotype may experience an adverse outcome after being prescribed codeine, tramadol, oxycodone, or hydrocodone. These medications are frequently prescribed for pain relief, and ~39% of the US population is expected to carry one of these phenotypes, suggesting that the population-level impact of these gene–drug interactions could be substantial.

Revisiting Oxycodone Analgesia: A Review and Hypothesis

Oxycodone, a semisynthetic opioid analgesic, is widely used in clinical practice. Oxycodone and morphine seem to be equally effective and equipotent; however, morphine is 10 times more potent than oxycodone when given epidurally. This article provides an updated review of the basic pharmacology of oxycodone with a special focus on pharmacokinetic/pharmacodynamics properties. The controversy regarding oxycodone-mediated effects for visceral pain via agonism and the possible role of peripheral opioid analgesia are discussed in the present investigation in an attempt to propose a plausible explanation to the perplexing question of oxycodone analgesia.

Pharmacogenetic Testing for Analgesic Adverse Effects: Pediatric Case Series

OBJECTIVES

Genetic variants in pharmacokinetic genes can alter the effectiveness and increase the risks of using analgesics to treat pain. The purpose of this retrospective study is to describe the clinical experiences that led to pharmacogenetic testing of pediatric pain management program patients for alterations in the CYP2D6, CYP2C19, and CYP2C9 genes and correlate the analgesic efficacy and adverse analgesic effects with the gene-specific findings and Metabolic Reserve (MR) index.

MATERIALS AND METHODS

Nineteen patients were referred for pharmacogenetic testing between February 2010 and December 2013 due to analgesic ineffectiveness or adverse analgesic effects. CYP2D6, CYP2C19, and CYP2C9 functional status was inferred from genotyping; and MR calculated. Data from the available inpatient and outpatient medical records from January 2007 to May 2014 for these patients were reviewed and extracted to characterize patient analgesic response phenotype.

RESULTS

Significant CYP2D6 genetic variants were identified in 16 of the 19 (84%) patients: 4 were ultra-rapid metabolizers, 8 were deficient, 3 were poor metabolizers, and 1 was CYP2D6 null metabolizer. Of the 3 patients with functional CYP2D6 status, 2 were CYP2C19 null metabolizers. The MR scores ranged from 3.0 to 7.0, with a bimodal distribution with high frequencies corresponding to 4.0/4.5 and 7.0.

DISCUSSION

Clinical evaluation of analgesic ineffectiveness and adverse effects led to the high likelihood of identifying patients with CYP2D6, CYP2C19, and CYP2C9 alleles associated with alterations in analgesic metabolism. Further research is needed to integrate pharmacogenetic and clinical information into anticipatory guidance for pharmacogenetic testing and analgesic prescribing to children with pain.

[Interindividual variation of pharmacokinetic disposition of and clinical responses to opioid analgesics in cancer pain patients]

Use of prescription opioids for cancer pain according to the World Health Organization analgesic ladder has been accepted in Japan. Although oxycodone and fentanyl are commonly used as first-line analgesics, a few clinical reports have been published on interindividual variations in their pharmacokinetics and clinical responses in cancer patients. (1) Some factors relating to CYP2D6, CYP3A, ATP-binding cassette sub-family B member 1 (ABCB1), and opioid receptor mu 1 (OPRM1) involve oxycodone pharmacokinetics and sensitivity in humans. The relations between their genetic variations and clinical responses to oxycodone are being revealed in limited groups. In our study, the impact of genetic variants and pharmacokinetics on clinical responses to oxycodone were evaluated in Japanese populations. (2) Opioid switching improves the opioid tolerance related to the balance between analgesia and adverse effects. Some patients have difficulty in obtaining better opioid tolerance in recommended conversion ratios. The activities of CYP3A, ABCB1, and OPRM1 contribute to the interindividual variations in clinical responses to fentanyl in cancer patients. However, the variations in opioid switching remain to be clarified in clinical settings. In our study, genetic factors related to interindividual variations in clinical responses in opioid switching to fentanyl were revealed in Japanese populations. In this symposium review, the possibility of approaches to personalized palliative care using opioids based on genetic variants of CYP2D6, CYP3A5, ABCB1, and OPRM1 is discussed.

Perspectives on Intravenous Oxycodone for Control of Postoperative Pain

Intravenous (IV) analgesia has particular advantages in the immediate postoperative period. For example, IV administration results in a faster onset of pain relief and results in more predictable pharmacokinetics than does administration by other routes. It also allows for convenient dosing before or during surgery, permitting the initiation of effective analgesia in the early phase of the postoperative period. In addition, when patients are able to tolerate oral intake, they can be switched from IV to oral dosing based on maintaining the predictable analgesia established by the IV route. IV morphine is widely used for the control of postoperative pain, but there is a trend toward the use of oxycodone. Oxycodone (which may be mediated partly through kappa- as well as mu-opioid receptors) offers several potential advantages. Published studies comparing IV oxycodone to other IV opioids for postsurgical pain report that oxycodone is a safe and effective analgesic. Some studies show that IV oxycodone may be associated with greater pain control, fewer or less severe adverse events, and faster onset of action, although the results are not consistent across all studies. Oxycodone has been reported to be safe in the geriatric and other special populations when adequate clinical adjustments are made. Thus, the clinical reports and oxycodone's pharmacologic profile make intravenous oxycodone a potentially important "new" old drug for postoperative pain control.

The role of cytochrome P450 pharmacogenomics in chronic non-cancer pain patients

INTRODUCTION

Pharmacogenomics is the field that studies an individualized treatment approach for patients' medication regimen that can impact drug safety, productivity, and personalized health care. Pharmacogenomics characterizes the genetic differences in metabolic pathways which can affect a patient's individual responses to drug treatments. Areas covered: The various responses to pharmacological agents are mainly determined by the different types of genetic variants of the CYP450. CYP2D6 polymorphism is well known for its variation in the metabolism of drugs from many therapeutic arenas, including some analgesic drugs such as codeine, hydromorphone, oxycodone and tramadol. Allele combinations determine the phenotypic expression, characterized as either: extensive metabolizer, intermediate metabolizer, ultra-rapid metabolizer and poor metabolizer. Expert opinion: The Human Genome Project (HGP) revolutionized the future of medicine and the way health care providers approach individualized patient treatment, and chronic pain management is one of those areas. The key findings in the literature appear to be related to the CYP2D6 expression and its high polymorphism influencing the metabolism of opioid medications, and the impact of that on the patient's therapeutic outcome thus exemplifying the importance of genetic testing for CYP2D6 in the process of physician therapeutic decision making.

Pharmacokinetic and pharmacodynamic evaluation of oxycodone and naltrexone for the treatment of chronic lower back pain

INTRODUCTION

Chronic low back pain (CLBP) is a common and difficult illness to manage. Some individuals with CLBP have pain processing disorders and are also at risk for opioid abuse, misuse; addiction and diversion. Guidelines have been published to guide management; neuromodulation, exercise, mindfulness-based stress reduction and cognitive behavior therapies among other non-pharmacological reduce the pain of CLBP with minimal toxicity. Pharmacological management includes acetaminophen, NSAIDs and antidepressants, mainly duloxetine. Abuse-deterrent opioids have been developed which have been shown to reduce pain and opioid abuse risk. ALO-02 is a tamper-resistant sustained release opioid consisting of extended release oxycodone and sequestered naltrexone. Pivotal studies of ALO-02 have centered on patients with CLBP.

AREAS COVERED

This manuscript will review CLBP, the pivotal analgesic and clinical abuse potential studies of ALO-02. The opinion will cover whether opioids should be used for CLBP, when they should be used and opioid choices.

EXPERT OPINION

ALO-02 is one of several opioids which can be considered in the management of CLBP. The outcome to a trial of opioids should be function rather than analgesia. Most analgesic trials for CLBP have had analgesia as the primary outcome and function has not been vigorously studied as an outcome. Opioids should be considered as a trial only when other non-opioid analgesics have failed to improve analgesia and function. Universal precautions should be routinely part of phase III analgesic trial particularly for chronic non-malignant pain.

A new therapeutic option for postoperative pain management with oxycodone HCI injection

Fentanyl is the most commonly used opioid analgesic in intravenous patient-controlled analgesia (IV PCA) in Korea. IV oxycodone was approved for postoperative IV PCA by the Ministry of Food and Drug Safety of Korea in 2013. The approved dosage regimen for postoperative pain relief with IV oxycodone is IV bolus loading of 2 mg followed by PCA composed of demand boluses of 1 mg and no background infusion with an oxycodone concentration of 1 mg/ml. However, a simulation study indicated that the minimum effective analgesic concentration (MEAC, as indicated by relief of pain by administering rescue analgesics) of oxycodone was reached most quickly with a higher loading dose of 0.1 mg/kg and IV PCA with background infusion. Oxycodone is a therapeutic option as an analgesic for postoperative pain management. It is necessary to reduce the analgesic dose of oxycodone in elderly patients because metabolic clearance decreases with age.

The pharmacogenetics of opioid therapy in the management of postpartum pain: a systematic review

AIMS

Opioids are commonly prescribed for postpartum pain. Yet, providing adequate pain relief, while ensuring that the mother and her breastfeeding infant are protected from adverse events can be challenging. The objective of this systematic review was to identify the role of opioid pharmacogenetics in analgesia and adverse events among patients being treated for postpartum pain, along with their breastfeeding infants.

METHODS

A comprehensive search of the literature was conducted in seven databases on June 3-4, 2015. Two reviewers independently screened studies for eligibility, extracted data and evaluated study quality using the Newcastle-Ottawa Scale.

RESULTS

Among the 2082 papers retrieved from the search, 17 were included in the review. These 17 papers consisted of various study designs, opioids, polymorphisms and patient outcomes. This systematic review reveals that CYP2D6, OPRM1 A118G, UGT2B7 C802T and ABCB1 G2677AT may contribute to postpartum analgesia or adverse events.

CONCLUSION

These findings may assist in personalizing care for patients receiving opioids during the postpartum period.

Cytochrome P450-mediated changes in oxycodone pharmacokinetics/pharmacodynamics and their clinical implications

In recent years the use of the opioid oxycodone has increased markedly and replacing morphine as the first-line choice of opioid in several countries. There are formulations for oral immediate, oral extended release and intravenous use. The bioavailability is higher than for morphine and less variable. Oxycodone is primarily metabolized in the liver by the cytochrome P450 (CYP) enzymes with CYP3A as the major metabolic pathway and CYP2D6 as the minor metabolic pathway to noroxycodone, oxymorphone and noroxymorphone. Oxycodone exerts its analgesic effect via the µ-opioid receptor. The metabolism of CYP2D6 substrates varies to a large degree between individuals as a result of allele functionality. Poor metabolizers (PM) have two non-functional alleles, extensive metabolizers (EM) are homozygous with two functional alleles or heterozygous with one functional allele and ultrarapid metabolizers (UM) have more than two functional alleles. There are pronounced interethnic differences in the allele distribution. On the basis of studies performed thus far, oxycodone concentrations in comparison with EM are similar in PM and reduced in UM. The pharmacokinetics in UM are insufficiently investigated. Simultaneous inhibition of both CYP3A and CYP2D6 results in increased oxycodone concentrations and such a combination should be avoided. A similar effect is to be expected with use of a CYP3A inhibitor in CYP2D6 PM. Concomitant use of enzyme inducers such as rifampicin, St John's wort and carbamazepine should be avoided because of the risk of subtherapeutic concentrations of oxycodone. When the dosage of morphine may result in unpredictable bioavailability, like in patients with severe hepatic cirrhosis, oxycodone might be beneficial because it has higher and less variability in bioavailability between patients than morphine.