Involvement of μ1-opioid receptor on oxycodone-induced antinociception in diabetic mice

Post-operative opioid-related adverse events with intravenous oxycodone compared to morphine: A randomized controlled trial

BACKGROUND

The value of intravenous oxycodone compared to morphine remains controversial. The purpose of this trial was to compare opioid-related adverse events (ORAES) of intravenous oxycodone and morphine after total hip arthroplasty.

METHODS

Patients scheduled for total hip arthroplasty were enrolled in this study of post-operative pain treatment with intravenous oxycodone or intravenous morphine (ratio 1:1). After surgery, patients received similar drug regimens for titration in the post-operative care unit followed by intravenous patient-controlled analgesia (PCA). The primary outcome was the number of patients with ≥1 ORAEs within the first 24 hours defined as either nausea, vomiting, respiratory depression, pruritus, urinary retention requiring evacuation, allergy, hallucinations. Secondary outcomes included pain scores and opioid consumption.

RESULTS

The analysis included 238 patients with similar characteristics. There were 55 patients with at least one ORAEs in the oxycodone group vs 46 in the morphine group: 48% vs 40%, P = .19; relative risk = 1.22 (0.91:1.63). Intravenous oxycodone vs intravenous morphine requirements were respectively (median, IQR): 6 (0-11) vs 8 (0-12) mg (P = .06) for titration, 15 (8-26) vs 8 (5-16) mg (P = .001) for PCA, and 22 (12-37) mg vs 19 (11-28) mg for cumulated intravenous consumption (P = .048). During the first 24 hours, there was no difference in secondary outcomes (oxycodone vs morphine, respectively, in %): nausea (15 vs 13), vomiting (5 vs 5), urinary retention (20 vs 12) or pain scores.

CONCLUSION

This study demonstrates that IV oxycodone did not significantly reduce ORAEs within the first 24 hours compared to similar ratio of IV morphine.

Role of Oxycodone Hydrochloride in Treating Radiotherapy-Related Pain

Radiotherapy is commonly used to treat cancer patients. Besides the curable effect, radiotherapy also could relieve the pain of cancer patients. However, cancer pain is gradually alleviated about two weeks after radiotherapy. In addition, cancer patients who receive radiotherapy may also suffer from pain flare or radiotherapy-induced side effects such as radiation esophagitis, enteritis, and mucositis. Pain control is reported to be inadequate during the whole course of radiotherapy (before, during, and after radiotherapy), and quality of life is seriously affected. Hence, radiotherapy is suggested to be combined with analgesic drugs in clinical guidelines. Previous studies have shown that radiotherapy combined with oxycodone hydrochloride can effectively alleviate cancer pain. In this review, we firstly presented the necessity of analgesia during the whole course of radiotherapy. We also sketched the role of oxycodone hydrochloride in radiotherapy of bone metastases and radiotherapy-induced oral mucositis. Finally, we concluded that oxycodone hydrochloride shows good efficacy and tolerance and could be used for pain management before, during, and after radiotherapy.

Medical Management of Pain in Chronic Pancreatitis

The medical management of pain in chronic pancreatitis continues to pose significant challenges for clinicians caring for these patients. There are increasing data, suggesting that pain in chronic pancreatitis is largely due to peripheral and central sensitization that evolves, over time, as a result of nociceptive afferent associated with chronic inflammation and fibrosis of the pancreas. In many instances, patients rapidly progress to requiring opioid analgesics for the adequate treatment of pain despite the unequivocal risks associated with the long-term use of these drugs. Centrally acting drugs, such as gabapentinoids, appear to be effective means of treating pain due to their inhibition of neurotransmitters involved in central sensitization, but side effects limit their use. The present review explores the evidence for various non-pharmacologic and pharmacologic treatments for pain in chronic pancreatitis.

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.

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.

Effects of Low-Dose Escherichia coli Lipopolysaccharide-Induced Endotoxemia on Morphine Pharmacokinetics in an Animal Model

OBJECTIVE

Systemic inflammation may change the bioavailability and pharmacokinetics of opioids. However, there are insufficient data on morphine pharmacokinetics in mild inflammatory conditions. This study aimed to determine the pharmacokinetics of morphine during low-dose endotoxemia in rabbits.

DESIGN

In two experiments (separated by a 14-day washout period), 10 rabbits received intravenous morphine at a dose of 3 mg/kg. In the second set of experiments, morphine infusion was preceded by low-dose endotoxemia induced with lipopolysaccharide (Escherichia coli 0111: B4) at a dose of 5 µg/kg. The kinetics of systemic morphine concentrations and chosen physiological parameters were measured at specific time intervals up to 6 hours after morphine administration.

RESULTS

In endotoxemia, decreased elimination half-life (P = 0.017), mean residence time (P = 0.022), and volume of distribution (P = 0.037) as well as an increased elimination rate constant (P = 0.013) and total body clearance (P = 0.023) were noted. The inverse linear correlation between morphine clearance versus the percentage (%) change in body temperature and pulse rate observed under control conditions was abolished under endotoxemia.

CONCLUSIONS

Low-dose endotoxemia is correlated with significant alterations in morphine pharmacokinetics in rabbits, leading to the faster elimination of the drug.

CLINICAL IMPLICATIONS

These findings may have important implications in patients with low-grade inflammation and imply the need to modify morphine dosing regimens to ensure optimal analgesia. The issue warrants further experimental and clinical investigation.

A6V polymorphism of the human μ-opioid receptor decreases signalling of morphine and endogenous opioids in vitro

BACKGROUND AND PURPOSE

Polymorphisms of the μ opioid receptor (MOPr) may contribute to the variation in responses to opioid drugs in clinical and unregulated situations. The A6V variant of MOPr (MOPr-A6V) is present in up to 20% of individuals in some populations, and may be associated with heightened susceptibility to drug abuse. There are no functional studies examining the acute signalling of MOPr-A6V in vitro, so we investigated potential functional differences between MOPr and MOPr-A6V at several signalling pathways using structurally distinct opioid ligands.

EXPERIMENTAL APPROACH

CHO and AtT-20 cells stably expressing MOPr and MOPr-A6V were used. AC inhibition and ERK1/2 phosphorylation were assayed in CHO cells; K channel activation was assayed in AtT-20 cells.

KEY RESULTS

Buprenorphine did not inhibit AC or stimulate ERK1/2 phosphorylation in CHO cells expressing MOPr-A6V, but buprenorphine activation of K channels in AtT-20 cells was preserved. [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, morphine and β-endorphin inhibition of AC was significantly reduced via MOPr-A6V, as was signalling of all opioids to ERK1/2. However, there was little effect of the A6V variant on K channel activation.

CONCLUSIONS AND IMPLICATIONS

Signalling to AC and ERK via the mutant MOPr-A6V was decreased for many opioids, including the clinically significant drugs morphine, buprenorphine and fentanyl, as well endogenous opioids. The MOPr-A6V variant is common and this compromised signalling may affect individual responses to opioid therapy, while the possible disruption of the endogenous opioid system may contribute to susceptibility to substance abuse.

Does the pharmacology of oxycodone justify its increasing use as an analgesic?

Oxycodone is a semisynthetic opioid analgesic that is increasingly used for the treatment of acute, cancer, and chronic non-malignant pain. Oxycodone was synthesized in 1917 but its pharmacological properties were not thoroughly studied until recently. Oxycodone is a fairly selective μ-opioid receptor agonist, but there is a striking discrepancy between the relatively low binding potential and G protein activation by oxycodone and its analgesic efficacy. It has been claimed that this is because of active metabolites and enhanced passage to the central nervous system by active transport. We critically review studies on the basic pharmacology of oxycodone and on its pharmacokinetics and pharmacodynamics in humans. In particular, the role of pharmacogenomics and population pharmacokinetics in understanding the properties of oxycodone is discussed in detail. We compare oxycodone with morphine, the standard opioid in clinical use.

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.

Opioid receptor subtypes: fact or artifact?

There is a vast amount of pharmacological evidence favouring the existence of multiple subtypes of opioid receptors. In addition to the primary classification of µ (mu: MOP), δ (delta: DOP), κ (kappa: KOP) receptors, and the nociceptin/orphanin FQ peptide receptor (NOP), various groups have further classified the pharmacological µ into µ(1-3), the δ into δ(1-2)/δ(complexed/non-complexed), and the κ into κ(1-3). From an anaesthetic perspective, the suggestions that µ(1) produced analgesia and µ(2) produced respiratory depression are particularly important. However, subsequent to the formal identification of the primary opioid receptors (MOP/DOP/KOP/NOP) by cloning and the use of this information to produce knockout animals, evidence for these additional subtypes is lacking. Indeed, knockout of a single gene (and hence receptor) results in a loss of all function associated with that receptor. In the case of MOP knockout, analgesia and respiratory depression is lost. This suggests that further sub-classification of the primary types is unwise. So how can the wealth of pharmacological data be reconciled with new molecular information? In addition to some simple misclassification (κ(3) is probably NOP), there are several possibilities which include: (i) alternate splicing of a common gene product, (ii) receptor dimerization, (iii) interaction of a common gene product with other receptors/signalling molecules, or (iv) a combination of (i)-(iii). Assigning variations in ligand activity (pharmacological subtypes) to one or more of these molecular suggestions represents an interesting challenge for future opioid research.

Determination of α(2)-adrenoceptor and imidazoline receptor involvement in augmentation of morphine and oxycodone analgesia by agmatine and BMS182874

Studies have demonstrated that clonidine (α(2)-adrenoceptor and imidazoline receptor agonist) and BMS182874 (endothelin ET(A) receptor antagonist) potentiate morphine and oxycodone analgesia. Agmatine, an endogenous clonidine-like substance, enhances morphine analgesia. However, its effect on oxycodone analgesia and its interaction with endothelin ET(A) receptor antagonists are not known. The present study was performed to determine the effect of agmatine on morphine and oxycodone analgesia and the involvement of α(2)-adrenoceptors, imidazoline receptors, opioid receptors, and endothelin receptors. Antinociception at various time intervals was determined by the tail-flick latency method in mice. Agmatine produced dose-dependent increase in tail-flick latency, while BMS182874 did not produce any change over the 360-min observation period. Agmatine significantly potentiated morphine as well as oxycodone analgesia which was not altered by BMS182874. BMS182874 pretreatment did not increase the analgesic effect produced by agmatine alone. Agmatine-induced potentiation of morphine and oxycodone analgesia was blocked by idazoxan (imidazoline receptor/α(2)-adrenoceptor antagonist) and yohimbine (α(2)-adrenoceptor antagonist). BMS182874-induced potentiation of morphine or oxycodone analgesia was not affected by yohimbine. However, idazoxan blocked BMS182874-induced potentiation of oxycodone but not morphine analgesia. This is the first report demonstrating that agmatine potentiates not only morphine but also oxycodone analgesia in mice. Potentiation of morphine and oxycodone analgesia by agmatine appears to involve α(2)-adrenoceptors, imidazoline receptors, and opioid receptors. In addition, imidazoline receptors may be involved in BMS182874-induced potentiation of oxycodone but not morphine analgesia. It is concluded that agmatine may be used as an adjuvant in opiate analgesia.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety

BACKGROUND AND PURPOSE

The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored.

EXPERIMENTAL APPROACH

We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed.

KEY RESULTS

CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers.

CONCLUSIONS AND IMPLICATIONS

The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

Visceral pain originating from the upper urinary tract

Pain originating from the upper urinary tract is a common problem and stone colic is one of the most intense pain conditions that can be experienced in the clinic. The pain is difficult to alleviate and often leads to medical attention. In humans, pain mechanisms of the upper urinary tract pain are still poorly understood, which often leads to a trial and error approach in clinical pain management. Pain from the upper urinary tract seems to have all the characteristics of pure visceral pain, including referred pain with or without hyperalgesia/trophic changes in somatic tissues and viscero-visceral hyperalgesia. However, further studies are needed to better understand these visceral pain mechanisms with regard to optimising pain management. This review gives an introduction to visceral pain in general and upper urinary tract pain in particular, with special reference to pain pathways and pharmacological and non-pharmacological pain modulation.

Regulation of gene expression in brain tissues of rats repeatedly treated by the highly abused opioid agonist, oxycodone: microarray profiling and gene mapping analysis

Although oxycodone is the most often used opioid agonist, it remains one of the most understudied drugs. We used microarray analysis to better understand the global changes in gene expression in brain tissues of rats repeatedly treated with oxycodone. Many genes were significantly regulated by oxycodone (e.g., Fkbp5, Per2, Rt1.Dalpha, Slc16a1, and Abcg2). Validation of the microarray data by quantitative real-time-polymerase chain reaction (Q-PCR) indicated that there was a strong significant correlation (r = 0.979, p < 0.0000001) between the Q-PCR and the microarray data. Using MetaCore (a computational platform), many biological processes were identified [e.g., organic anion transport (p = 7.251 x 10(-4)) and regulation of immune response (p = 5.090 x 10(-4))]. Among the regulated genes, Abcg2 mRNA was up-regulated by 2.1-fold, which was further confirmed by immunoblotting (1.8-fold up-regulation). Testing the Abcg2 affinity status of oxycodone using an Abcg2 ATPase assay suggests that oxycodone behaves as an Abcg2 substrate only at higher concentrations (> or = 500 microM). Furthermore, brain uptake studies demonstrated that oxycodone-induced Abcg2 up-regulation resulted in a significant (p < 0.05) decrease (approximately 2-fold) in brain/plasma ratios of mitoxantrone. These results highlight markers/mediators of neuronal responses and identify regulatory pathways involved in the pharmacological action of oxycodone. These results also identify genes that potentially modulate tolerance, dependence, immune response, and drug-drug interactions. Finally, our findings suggest that oxycodone-induced up-regulation of Abcg2 enhanced the efflux of the Abcg2 substrate, mitoxantrone, limiting its brain accumulation and resulting in an undesirable drug-drug interaction. Extrapolating these results to other Abcg2 substrates (e.g., daunorubicin and doxorubicin) indicates that the brain uptake of these agents may be affected if they are administered concomitantly with oxycodone.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.