Liposolubility and protein binding of oxycodone in vitro

Exploring the impact of CYP2D6 and UGT2B7 gene-drug interactions, and CYP-mediated DDI on oxycodone and oxymorphone pharmacokinetics using physiologically-based pharmacokinetic modeling and simulation

Oxycodone is one of the most commonly used opioids to treat moderate to severe pain. It is metabolized mainly by CYP3A4 and CYP2D6, while only a small fraction of the dose is excreted unchanged into the urine. Oxymorphone, the metabolite primarily formed by CYP2D6, has a 40- to 60-fold higher mu-opioid receptor affinity than the parent compound. While CYP2D6-mediated gene-drug-interactions (GDIs) and drug-drug interactions (DDIs) are well-studied, they only account for a portion of the variability in oxycodone and oxymorphone exposure. The combined impact of CYP2D6-mediated GDIs and DDIs, CYP3A4-mediated DDIs, and UGT2B7 GDIs is not fully understood yet and hard to study in head-to-head clinical trials given the relatively large number of scenarios. Instead, we propose the use of a physiologically-based pharmacokinetic model that integrates available information on oxycodone's metabolism to characterize and predict the impact of DDIs and GDIs on the exposure of oxycodone and its major, pharmacologically-active metabolite oxymorphone. To this end, we first developed and verified a PBPK model for oxycodone and its metabolites using published clinical data. The verified model was then applied to determine the dose-exposure relationship of oxycodone and oxymorphone stratified by CYP2D6 and UGT2B7 phenotypes respectively, and administered perpetrators of CYP-based drug interactions. Our simulations demonstrate that the combination of CYP2D6 UM and a UGT2B7Y (268) mutation may lead to a 2.3-fold increase in oxymorphone exposure compared to individuals who are phenotyped as CYP2D6 NM / UGT2B7 NM. The extent of oxymorphone exposure increases up to 3.2-fold in individuals concurrently taking CYP3A4 inhibitors, such as ketoconazole. Inhibition of the CYP3A4 pathway results in a relative increase in the partial metabolic clearance of oxycodone to oxymorphone. Oxymorphone is impacted to a higher extent by GDIs and DDIs than oxycodone. We predict oxymorphone exposure to be highest in CYP2D6 UMs/UGT2B7 PMs in the presence of ketoconazole (strong CYP3A4 index inhibitor) and lowest in CYP2D6 PMs/UGT2B7 NMs in the presence of rifampicin (strong CYP3A4 index inducer) covering a 55-fold exposure range.

First evidence of environmental bioaccumulation of pharmaceuticals on adult native anurans (Rhinella arenarum) from Argentina

The presence of pharmaceutically active compounds (PhACs) in surface water is well known, whereas their natural occurrence in biota is much less explored. The aim of this work was to evaluate the bioaccumulation of PhACs in adult toads of the neotropical species Rhinella arenarum. Three sites were selected in Buenos Aires (Argentina): a reference site (Site 1), a site with direct discharge from a secondary wastewater treatment plant (WWTP) (Site 2) and a site 300 m downstream of the WWTP discharge (Site 3). Surface water samples, as well as muscle, liver and fat bodies of toads were collected, extracted and analyzed by LC-MS/MS. Highly significant differences in total PhACs concentration in surface water (p < 0.005) were detected between Site 2 and the other sites. These concentrations ranged from 0.37 to 52.46 ng/L at Site 1, 0.71-6950.37 ng/L at Site 2, and 0.12-75.45 ng/L at Site 3. In general, bioaccumulation of PhACs in toad tissues was similar between sites and tissues of each site. The highest concentrations were detected in the muscle of toads from Site 3 (1.06-87.24 ng/g dw), followed by liver (1.77-38.10 ng/g dw) and fat bodies (0.68-20.59 ng/g dw) from Site 1. Ibuprofen (6950 ng/L), acetaminophen (3277 ng/L) and valsartan (2504 ng/L) were the compounds with the highest concentrations in surface water from Site 2, whereas acetaminophen (87.2 ng/g dw, muscle from Site 3), desloratadine (38.1 ng/g dw, liver from Site 1), and phenazone (25.9 ng/g dw, liver from Site 1) were the ones that showed the highest concentrations in biota. This is the first time a field study has examined the environmental bioaccumulation of PhACs in anurans, demonstrating their potential for monitoring the status of natural ecosystems.

Epidural Oxycodone for Acute Pain

Epidural analgesia is commonly used in labour analgesia and in postoperative pain after major surgery. It is highly effective in severe acute pain, has minimal effects on foetus and newborn, may reduce postoperative complications, and enhance patient satisfaction. In epidural analgesia, low concentrations of local anaesthetics are combined with opioids. Two opioids, morphine and sufentanil, have been approved for epidural use, but there is an interest in evaluating other opioids as well. Oxycodone is one of the most commonly used opioids in acute pain management. However, data on its use in epidural analgesia are sparse. In this narrative review, we describe the preclinical and clinical data on epidural oxycodone. Early data from the 1990s suggested that the epidural administration of oxycodone may not offer any meaningful benefits over intravenous administration, but more recent clinical data show that oxycodone has advantageous pharmacokinetics after epidural administration and that epidural administration is more efficacious than intravenous administration. Further studies are needed on the safety and efficacy of continuous epidural oxycodone administration and its use in epidural admixture.

A review of pregnancy-induced changes in opioid pharmacokinetics, placental transfer, and fetal exposure: Towards fetomaternal physiologically-based pharmacokinetic modeling to improve the treatment of neonatal opioid withdrawal syndrome

Physiologically-based pharmacokinetic (PBPK) modeling has emerged as a useful tool to study pharmacokinetics (PK) in special populations, such as pregnant women, fetuses, and newborns, where practical hurdles severely limit the study of drug behavior. PK in pregnant women is variable and everchanging, differing greatly from that in their nonpregnant female and male counterparts typically enrolled in clinical trials. PBPK models can accommodate pregnancy-induced physiological and metabolic changes, thereby providing mechanistic insights into maternal drug disposition and fetal exposure. Fueled by the soaring opioid epidemic in the United States, opioid use during pregnancy continues to rise, leading to an increased incidence of neonatal opioid withdrawal syndrome (NOWS). The severity of NOWS is influenced by a complex interplay of extrinsic and intrinsic factors, and varies substantially between newborns, but the extent of prenatal opioid exposure is likely the primary driver. Fetomaternal PBPK modeling is an attractive approach to predict in utero opioid exposure. To facilitate the development of fetomaternal PBPK models of opioids, this review provides a detailed overview of pregnancy-induced changes affecting the PK of commonly used opioids during gestation. Moreover, the placental transfer of these opioids is described, along with their disposition in the fetus. Lastly, the implementation of these factors into PBPK models is discussed. Fetomaternal PBPK modeling of opioids is expected to provide improved insights in fetal opioid exposure, which allows for prediction of postnatal NOWS severity, thereby opening the way for precision postnatal treatment of these vulnerable infants.

Integrated Systems Analysis of Mixed Neuroglial Cultures Proteome Post Oxycodone Exposure

Opioid abuse has become a major public health crisis that affects millions of individuals across the globe. This widespread abuse of prescription opioids and dramatic increase in the availability of illicit opioids have created what is known as the opioid epidemic. Pregnant women are a particularly vulnerable group since they are prescribed for opioids such as morphine, buprenorphine, and methadone, all of which have been shown to cross the placenta and potentially impact the developing fetus. Limited information exists regarding the effect of oxycodone (oxy) on synaptic alterations. To fill this knowledge gap, we employed an integrated system approach to identify proteomic signatures and pathways impacted on mixed neuroglial cultures treated with oxy for 24 h. Differentially expressed proteins were mapped onto global canonical pathways using ingenuity pathway analysis (IPA), identifying enriched pathways associated with ephrin signaling, semaphorin signaling, synaptic long-term depression, endocannabinoid signaling, and opioid signaling. Further analysis by ClueGO identified that the dominant category of differentially expressed protein functions was associated with GDP binding. Since opioid receptors are G-protein coupled receptors (GPCRs), these data indicate that oxy exposure perturbs key pathways associated with synaptic function.

Electrochemical Detection of Morphine in Untreated Human Capillary Whole Blood

Disposable single-use electrochemical sensor strips were used for quantitative detection of small concentrations of morphine in untreated capillary whole blood. Single-walled carbon nanotube (SWCNT) networks were fabricated on a polymer substrate to produce flexible, reproducible sensor strips with integrated reference and counter electrodes, compatible with industrial-scale processes. A thin Nafion coating was used on top of the sensors to enable direct electrochemical detection in whole blood. These sensors were shown to detect clinically relevant concentrations of morphine both in buffer and in whole blood samples. Small 38 μL finger-prick blood samples were spiked with 2 μL of morphine solution of several concentrations and measured without precipitation of proteins or any other further pretreatment. A linear range of 0.5-10 μM was achieved in both matrices and a detection limit of 0.48 μM in buffer. In addition, to demonstrate the applicability of the sensor in a point-of-care device, single-determination measurements were done with capillary samples from three subjects. An average recovery of 60% was found, suggesting that the sensor only measures the free, unbound fraction of the drug. An interference study with other opioids and possible interferents showed the selectivity of the sensor. This study clearly indicates that these Nafion/SWCNT sensor strips show great promise as a point-of-care rapid test for morphine in blood.

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.

Pharmacotherapy of neonatal opioid withdrawal syndrome: a review of pharmacokinetics and pharmacodynamics

INTRODUCTION

Neonatal opioid withdrawal syndrome (NOWS) often arises in infants born to mothers who used opioids during pregnancy. Morphine, methadone, and buprenorphine are the most common first-line treatments, whereas clonidine and phenobarbital are generally reserved for adjunctive therapy. These drugs exhibit substantial pharmacokinetic (PK) and pharmacodynamic (PD) variability. Current pharmacological treatments for NOWS are based on institutional protocols and largely rely on empirical treatment of patient symptoms.

AREAS COVERED

This article reviews the PK/PD of NOWS pharmacotherapies with a focus on the implication of physiological development and maturation. Body size-standardized clearance is consistently low in neonates, except for methadone. This can be ascribed to underdeveloped metabolic and elimination pathways. The effects of pharmacogenetics have been clarified especially for morphine. The PK/PD relationship of medications used in the treatment of NOWS is generally understudied.

EXPERT OPINION

Providing an appropriate opioid dose in neonates is challenging. Advancements in quantitative pharmacology and PK/PD modeling approaches facilitate identification of key factors driving PK/PD variability and characterization of exposure-response relationships. PK/PD model-informed simulations have been widely employed to define age-appropriate pediatric dosing regimens. The model-informed approach holds promise to aid more rational use of medications in the treatment of NOWS.

Comparison of Analgesic and Adverse Effects of Oxycodone- and Fentanyl-Based Patient-Controlled Analgesia in Patients Undergoing Robot-Assisted Laparoscopic Gastrectomy Using a 55:1 Potency Ratio of Oxycodone to Fentanyl: A Retrospective Study

Purpose

Oxycodone has affinities for both kappa- and mu-opioid receptors. Therefore, it has been used for postoperative analgesia of surgeries in which visceral pain is expected to be the main cause of pain. However, there are few studies of the 55:1 potency ratio of oxycodone to fentanyl when using it as intravenous patient-controlled analgesia (IV-PCA). Thus, we compared the analgesic and adverse effects of IV-PCA using the 55:1 potency ratio of oxycodone to fentanyl in patients who underwent robot-assisted laparoscopic gastrectomy.

Patients and Methods

This retrospective study included 100 patients using an automatic PCA pump with oxycodone or fentanyl who underwent robot-assisted laparoscopic gastrectomy between January and November 2017. All patients were provided with an IV-PCA consisting of 20 μg/kg of fentanyl or 1.1 mg/kg of oxycodone mixed with 0.9% normal saline solution to a total volume of 250 mL, which was infused basally at a rate of 0.1 mL/h with a bolus dose of 1 mL and lockout time of 6 min. The primary and secondary endpoints were to evaluate the efficacies of IV-PCA using the 55:1 potency ratio of oxycodone to fentanyl on analgesic and adverse effects.

Results

Pain intensity on arrival at the post-anesthesia care unit (PACU; 3.6±1.4 vs 4.4±2.0, P=0.031) and additional analgesic requirement within an hour after surgery (including the PACU period) (12% vs 37%; P=0.005) were significantly lower in the oxycodone group (n=49) than in the fentanyl group (n=51). Regarding adverse effects, the rate of postoperative nausea within 1 h after surgery (2% vs 16%; P=0.031) was also significantly lower in the oxycodone group than that in the fentanyl group.

Conclusion

Oxycodone-based IV-PCA by dose calculations with a 55:1 potency ratio may achieve better analgesia without any significant adverse effects, when using IV-PCA in patients undergoing robot-assisted laparoscopic gastrectomy.

Protracted renal clearance of fentanyl in persons with opioid use disorder

INTRODUCTION

The illicit opioid supply in the U.S. is increasingly adulterated with fentanyl. As such, persons with opioid use disorder (OUD) may be regularly exposed to fentanyl, however, the pharmacokinetics of repeated fentanyl exposure are not well understood. The current study aimed to quantify renal clearance of fentanyl in OUD patients presenting to residential treatment.

METHODS

Participants (N = 12) who presented to a 28-day residential treatment program were enrolled if they tested positive for fentanyl at intake. Urine samples were collected every 2-3 days and were quantitatively tested for fentanyl, norfentanyl, and creatinine via liquid chromatography mass spectrometry (LC-MS). Fentanyl clearance was defined as the time since last illicit opioid use and the median time between last positive and first negative fentanyl urine screen.

RESULTS

Participants had a mean and standard deviation (SD) age of 28.9 (11.0), were 67 % male, and 83 % white. The mean (SD) time for fentanyl and norfentanyl clearance was 7.3 (4.9) and 13.3 (6.9) days, respectively. One participant continued to test positive for fentanyl for 19 days and norfentanyl for 26 days following their last use, and left treatment without testing negative for norfentanyl.

CONCLUSION

Fentanyl clearance in persons with OUD is considerably longer than the typical 2-4 day clearance of other short-acting opioids. The findings of this study might explain recent reports of difficulty in buprenorphine inductions for persons who use fentanyl, and point to a need to better understand the pharmacokinetics of fentanyl in the context of opioid withdrawal in persons who regularly use fentanyl.

Method for Successfully Inducting Individuals Who Use Illicit Fentanyl Onto Buprenorphine/Naloxone

BACKGROUND AND OBJECTIVES

Individuals exposed to fentanyl are at risk of precipitated withdrawal using typical buprenorphine/naloxone induction procedures.

METHODS

This case series describes buprenorphine/naloxone inductions of four individuals who tested positive for fentanyl.

RESULTS

Buprenorphine-precipitated withdrawal was observed in two individuals who completed a conventional buprenorphine/naloxone induction strategy. Two more individuals completed a revised buprenorphine/naloxone induction strategy that did not precipitate withdrawal.

DISCUSSION AND CONCLUSION

Using multiple 2 mg doses of buprenorphine/naloxone in patients already in mild/moderate withdrawal improved outcomes.

SCIENTIFIC SIGNIFICANCE

Persons who use illicit fentanyl might be less likely to experience precipitated withdrawal from this revised buprenorphine/naloxone induction strategy. (Am J Addict 2021;30:83-87).

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.

Characteristics and circumstances of heroin and pharmaceutical opioid overdose deaths: Comparison across opioids

BACKGROUND

Although much is known about the correlates of heroin overdose, less is known about pharmaceutical opioid (PO) overdose. This study aimed to examine correlates of opioid overdose deaths by opioid and compare correlates between opioids.

METHODS

Analysis of opioid overdose deaths in Australia between 2000-2015, extracted from the National Coronial Information System (NCIS). The NCIS is an online database of deaths reportable to the coroner, and contains coroner's findings, autopsy and toxicology reports. Deaths were categorized into mutually exclusive groups: 1) Heroin deaths; and 2) PO deaths (excluding heroin). PO deaths were examined by individual opioid.

RESULTS

There were 10,795 opioid overdose deaths over the study period. Relative to deaths occurring in major cities, deaths in regional/remote areas had 15.2 (95 % CI: 11.5-20.2) times the risk of being attributed to pharmaceutical fentanyl than heroin. Relative to deaths among people without a recorded history of chronic pain, deaths among people with a recorded history of chronic pain had a 1.9-10.7-fold increased risk of the death being attributed to POs than heroin. Deaths among people with a recorded history of substance use problems where the opioid was injected prior to death had 7.2 and 1.7 times the risk of being attributed to methadone and pharmaceutical fentanyl (respectively) than heroin.

CONCLUSIONS

Findings suggest the need to: educate PO consumers about the risks of overdose at the time of prescribing; increase coverage and engagement in opioid dependence treatment (particularly in regional/remote areas); and increase uptake of take-home naloxone to reduce opioid overdose mortality.

Nonclinical safety assessment of PF614: A novel TAAP prodrug of oxycodone for chronic pain indication

PF614, a novel trypsin activated abuse protection (TAAP) prodrug of oxycodone, is being studied as chronic pain analgesic with extended release and abuse resistant properties. A series of nonclinical safety studies were conducted to support PF614 introduction to clinical trials. Ames assays (PF614 and its metabolites), comet assay (PF614 ≤ 50 mg/kg/day oral gavage in rats) and micronucleus assay (PF614 ≤ 175 mg/kg/day oral gavage in rats) were negative. hERG assay IC50 for PF614 was ≥300 μM. PF614 (0.1 and 10 μM) showed a low permeability in Caco-2 cells (≤1.17 x 10-6 cm/s) and was not a P-gp or BCRP substrate or inhibitor. The mean percent unbound PF614 among all concentrations in plasma ranged from 91.2 to 98.4, 79.4 to 100, and 52.9-79.9% in rat, dog, and human, respectively. Also, PF614 was metabolically stable in rat, dog, and human hepatocytes with no metabolites identified. Safety pharmacology study in dog indicated moderately lower heart rate at ≥ 2 mg/kg oral gavage doses. Toxicity studies of PF614 in rat and dog with daily oral doses of 25 and 18 mg/kg, respectively, for 14 Days were well tolerated with favorable safety profile supporting its further clinical evaluation.

Analgesic efficacy and pharmacokinetics of epidural oxycodone in pain management after gynaecological laparoscopy-A randomised, double blind, active control, double-dummy clinical comparison with intravenous administration

AIMS

Early pain after laparoscopy is often severe. Oxycodone is a feasible analgesic option after laparoscopy, but there are sparse data on epidural administration. The aim was to evaluate the analgesic efficacy and pharmacokinetics of a single dose of epidural oxycodone as a part of multimodal analgesia after gynaecological laparoscopy.

METHODS

Women (n = 60), aged 23-71 years, undergoing elective gynaecological laparoscopy, were administrated either epidural oxycodone 0.1 mg kg^-1 and intravenous (i.v.) saline (EPI-group n = 31), or epidural saline and i.v. oxycodone 0.1 mg kg^-1 (IV-group = 29) in a randomised, double blind, active control, double dummy clinical trial. A pharmacokinetic model was developed using population modelling of plasma and cerebrospinal fluid (CSF) concentrations obtained in these patients and data of 2 published studies. The primary outcome was the amount of i.v. fentanyl for rescue analgesia during the first 4 hours.

RESULTS

Twenty of the 31 patients in the EPI-group and 26 of the 29 patients in the IV-group needed i.v. fentanyl for rescue analgesia, P = .021. The median (interquartile range) number of fentanyl doses were 1.0 (1.0-3.0) in the EPI-group and 2.5 (1.0-4.0) doses in the IV-group, P = .008. Plasma concentrations were similar, but CSF concentrations were 100-fold higher in the EPI-group. The population model indicated that 60% of oxycodone injected into the epidural space enters into CSF and 40% is absorbed into the systemic circulation.

CONCLUSIONS

The data support superiority of epidural administration of oxycodone compared to i.v. administration during the first hours after laparoscopic surgery. This is likely to be based on enhanced permeation into the central nervous system after epidural administration.

Dexmedetomidine enhances glymphatic brain delivery of intrathecally administered drugs

Drug delivery to the central nervous system remains a major problem due to biological barriers. The blood-brain-barrier can be bypassed by administering drugs intrathecally directly to the cerebrospinal fluid (CSF). The glymphatic system, a network of perivascular spaces promoting fluid exchange between CSF and interstitial space, could be utilized to enhance convective drug delivery from the CSF to the parenchyma. Glymphatic flow is highest during sleep and anesthesia regimens that induce a slow-wave sleep-like state. Here, using mass spectrometry and fluorescent imaging techniques, we show that the clinically used α₂-adrenergic agonist dexmedetomidine that enhances EEG slow-wave activity, increases brain and spinal cord drug exposure of intrathecally administered drugs in mice and rats. Using oxycodone, naloxone, and an IgG-sized antibody as relevant model drugs we demonstrate that modulation of glymphatic flow has a distinct impact on the distribution of intrathecally administered therapeutics. These findings can be exploited in the clinic to improve the efficacy and safety of intrathecally administered therapeutics.

Frequency and severity of non-fatal opioid overdoses among clients attending the Sydney Medically Supervised Injecting Centre

BACKGROUND

Pharmaceutical opioid overdose rates have increased in recent years. The current study aimed to compare rates per 1000 injections of non-fatal overdose after heroin or oxycodone injection, and their comparative clinical severity.

METHODS

Analysis of prospectively collected data from the Sydney Medically Supervised Injecting Centre (MSIC). Severity of overdose was measured using the Glasgow Coma Scale, oxygen saturation levels, and the administration of naloxone.

RESULTS

Heroin overdoses occurred at three times the rate of oxycodone overdoses (12.7 v 4.1 per 1000 injections). Heroin overdoses appeared to be more severe than oxycodone overdoses, with higher levels of compromised consciousness (31 v 18%) and severe respiratory depression (67 v 48%), but there were no differences in naloxone doses (20 v 17%). Concurrent use of other depressants at the time of overdose was also associated with compromised consciousness, and the need for naloxone.

CONCLUSIONS

Heroin overdoses occurred at a greater rate than oxycodone overdoses, and had more severe clinical indicators.

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.

Analgesic efficacy, adverse effects, and safety of oxycodone administered as continuous intravenous infusion in patients after total hip arthroplasty

Background

Total hip arthroplasty (THA) causes extensive tissue damage and severe pain. This study aimed to assess the analgesic efficacy, adverse effects (AEs), and safety of continuous intravenous (iv) oxycodone infusion with ketoprofen (injected into the iv line) in patients after THA, and to assay serum oxycodone levels.

Patients and methods

Fourteen patients, aged 59‒82 years with American Society of Anesthesiologists (ASA) classification I or III, underwent THA with intrathecal analgesia and sedation induced by iv propofol. After the surgery, oxycodone (continuous iv infusion) at a dose of 1 mg/h (five patients) or 2 mg/h (nine patients) with 100 mg ketoprofen (injected into the iv line) was administered to each patient every 12 h. Pain was assessed using a numerical rating scale (NRS: 0 – no pain, 10 – the most severe pain) at rest and during movement. AEs, including hemodynamic unsteadiness, nausea, vomiting, pruritus, cognitive impairment, and respiratory depression, were registered during the first 24 h after surgery.

Results

Oxycodone (continuous iv infusion) at a dose of 2 mg/h with ketoprofen (100 mg) administered every 12 h provided satisfactory analgesia in all nine patients without the need of rescue analgesics within the first 24 h after THA. In three out of five patients, oxycodone at 1 mg/h was effective. Oxycodone did not induce drowsiness, vomiting, pruritus, respiratory depression, or changes in blood pressure. Bradycardia appeared in two patients, and nausea was observed in one patient.

Conclusion

Oxycodone infusion with ketoprofen administered by iv is effective in patients after THA. Intravenous infusion of oxycodone is a predictable, stable, and safe method of drug administration.

Design and evaluation of an extended-release matrix tablet formulation; the combination of hypromellose acetate succinate and hydroxypropylcellulose

The purpose of this study was to develop an extended-release (ER) matrix tablet that shows robust dissolution properties able to account for the variability of pH and mechanical stress in the GI tract using a combination of enteric polymer and hydrophilic polymer. Hypromellose acetate succinate (HPMCAS) and hydroxypropylcellulose (HPC) were selected as ER polymers for the ER matrix tablet (HPMCAS/HPC ER matrix tablet). Oxycodone hydrochloride was employed as a model drug. Dissolution properties of the HPMCAS/HPC ER matrix tablets were evaluated and were not affected by the pH of the test medium or paddle rotating speed. In a USP apparatus 3 (bio-relevant dissolution method), dissolution profiles of the HPMCAS/HPC ER matrix tablets containing oxycodone hydrochloride were similar to that of the reference product (OxyContin). Moreover, in vivo performance after oral administration of the HPMCAS/HPC ER matrix tablets to humans was simulated by GastroPlus based on dissolution profiles from the USP apparatus 3. The plasma concentration-time profile simulated was similar to that of the reference product. These results suggest that the combination of HPMCAS and HPC shows a robust dissolution profile against pH and paddle rotating speed and indicates the appropriate extended-release profile in humans.

Opioid Concentrations in Oral Fluid and Plasma in Cancer Patients With Pain

CONTEXT

Measuring opioid concentrations in pain treatment is warranted in situations where optimal opioid analgesia is difficult to reach.

OBJECTIVES

To assess the usefulness of oral fluid (OFL) as an alternative to plasma in opioid concentration monitoring in cancer patients on chronic opioid therapy.

METHODS

We collected OFL and plasma samples from 64 cancer patients on controlled-release (CR) oral morphine, CR oral oxycodone, or transdermal (TD) fentanyl for pain. Samples were obtained on up to five separate days.

RESULTS

A total of 213 OFL and plasma samples were evaluable. All patients had detectable amounts of the CR or TD opioid in both plasma and OFL samples. The plasma concentrations of oxycodone and fentanyl (determination coefficient R(2) = 0.628 and 0.700, respectively), but not morphine (R(2) = 0.292), were moderately well correlated to the daily opioid doses. In contrast to morphine and fentanyl (mean OFL/plasma ratio 2.0 and 3.0, respectively), the OFL oxycodone concentrations were significantly higher than the respective plasma concentrations (mean OFL/plasma ratio 14.9). An active transporter could explain the much higher OFL vs. plasma concentrations of oxycodone compared with morphine and fentanyl.

CONCLUSION

OFL analysis is well suited for detecting the studied opioids. For morphine and fentanyl, an approximation of the plasma opioid concentrations is obtainable, whereas for oxycodone, the OFL/plasma concentration relationship is too variable for reliable approximation results.

In vivo profiling of seven common opioids for antinociception, constipation and respiratory depression: no two opioids have the same profile

BACKGROUND AND PURPOSE

For patients experiencing inadequate analgesia and intolerable opioid-related side effects on one strong opioid analgesic, pain relief with acceptable tolerability is often achieved by rotation to a second strong opioid. These observations suggest subtle pharmacodynamic differences between opioids in vivo. This study in rats was designed to assess differences between opioids in their in vivo profiles.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were given single i.c.v. bolus doses of morphine, morphine-6-glucuronide (M6G), fentanyl, oxycodone, buprenorphine, DPDPE ([D-penicillamine(2,5) ]-enkephalin) or U69,593. Antinociception, constipation and respiratory depression were assessed using the warm water tail-flick test, the castor oil-induced diarrhoea test and whole body plethysmography respectively.

KEY RESULTS

These opioid agonists produced dose-dependent antinociception, constipation and respiratory depression. For antinociception, morphine, fentanyl and oxycodone were full agonists, buprenorphine and M6G were partial agonists, whereas DPDPE and U69,593 had low potency. For constipation, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, morphine produced a bell-shaped dose-response curve, whereas DPDPE and U69,593 were inactive. For respiratory depression, morphine, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, whereas DPDPE and U69,593 were inactive. The respiratory depressant effects of fentanyl and oxycodone were of short duration, whereas morphine, M6G and buprenorphine evoked prolonged respiratory depression.

CONCLUSION AND IMPLICATIONS

For the seven opioids we assessed, no two had the same profile for evoking antinociception, constipation and respiratory depression, suggesting that these effects are differentially regulated. Our findings may explain the clinical success of 'opioid rotation'.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

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.

Pharmacokinetics of oxycodone after subcutaneous administration in a critically ill population compared with a healthy cohort

This study aimed to characterise and compare the absorption pharmacokinetics of a single subcutaneous dose of oxycodone in critically ill patients and healthy subjects. Blood samples taken at intervals from two minutes to eight hours after a subcutaneous dose of oxycodone in patients (5 mg) and healthy volunteers (10 mg) were assayed using high performance liquid chromatography. Data were analysed using a non-compartmental approach and presented as mean (SD). Parameters were corrected for dose differences between the groups assuming linear kinetics. Ten patients (eight male, two female) and seven healthy male subjects were included. Maximum venous concentration and area under the concentration curve were approximately two-fold lower in the patient group for an equivalent dose, suggesting either reduced bioavailability or increased clearance: maximum venous concentration 0.14 ± 0.06 vs 0.05 ± 0.02 µg/ml (P <0.0001); area under the concentration curve 19.50 ± 9.15 vs 9.72 ± 2.71 µg/ml/minute (P <0.001) respectively. However, time to maximum venous concentration and mean residence time were not different, suggesting similar absorption rates: time to maximum venous concentration 22.10 ± 18.0 vs 20.50 ± 16.10 minutes (P=0.81); mean residence time 353 ± 191 vs 291 ± 80 minutes (P=0.26). Kinetic parameters were less variable in patients than in volunteers. The patients therefore had reduced exposure to subcutaneous oxycodone. This warrants further model-based analysis and experimentation. Dose regimens for subcutaneous oxycodone developed in healthy volunteers cannot be directly translated to critically ill patients.

Impact of cachexia on pharmacokinetic disposition of and clinical responses to oxycodone in cancer patients

PURPOSE

Cancer cachexia is characterized by hypoalbuminemia and with the hepatic production of acute-phase proteins in response to malignant growth. The aim of this study was to evaluate the influence of cachexia on the pharmacokinetic disposition of and clinical responses to oxycodone in cancer patients.

METHODS

Forty-seven Japanese patients receiving oxycodone extended-release tablets as a starting opioid for cancer pain were enrolled in this study. Cachexia was evaluated using the Glasgow Prognostic Score (GPS). Predose plasma concentrations of oxycodone and noroxycodone were determined at the titration dose.

RESULTS

Seven patients had a GPS of 0, 21 a GPS of 1, and 19 had a GPS of 2. A higher GPS was significantly correlated with a higher oxycodone concentration and a lower concentration ratio of noroxycodone to oxycodone and significantly associated with a lower incidence of dose escalation and a higher incidence of central adverse reactions. Serum albumin, but not α(1)-acid glycoprotein and C-reactive protein, was inversely correlated with the free fraction of oxycodone. Serum albumin concentration was significantly associated with the incidence of dose escalation. In contrast, the free fraction of oxycodone and acute-phase proteins were not related to the clinical responses.

CONCLUSIONS

Cachexia had an effect on oxycodone metabolism and the clinical responses to oxycodone. The observed reduction in serum albumin concentration was associated with dose escalation. These findings suggest that cachexia affects the clinical responses to oxycodone through metabolic and nutritional disorders in cancer patients.

Metabolism of oxycodone in human hepatocytes from different age groups and prediction of hepatic plasma clearance

Oxycodone is commonly used to treat severe pain in adults and children. It is extensively metabolized in the liver in adults, but the maturation of metabolism is not well understood. Our aim was to study the metabolism of oxycodone in cryopreserved human hepatocytes from different age groups (3 days, 2 and 5  months, 4  years, adult pool) and predict hepatic plasma clearance of oxycodone using these data. Oxycodone (0.1, 1, and 10 μM) was incubated with hepatocytes for 4 h, and 1 μM oxycodone also with CYP3A inhibitor ketoconazole (1 μM). Oxycodone and noroxycodone concentrations were determined at several time points with liquid chromatography-mass spectrometry. In vitro clearance of oxycodone was used to predict hepatic plasma clearance, using the well-stirred model and published physiological parameters. Noroxycodone was the major metabolite in all batches and ketoconazole inhibited the metabolism markedly in most cases. A clear correlation between in vitro oxycodone clearance and CYP3A4 activity was observed. The predicted hepatic plasma clearances were typically much lower than the published median total plasma clearance from pharmacokinetic studies. The data suggests that there are no children-specific metabolites of oxycodone. Moreover, CYP3A activity seems to be the major determinant in metabolic clearance of oxycodone regardless of age group or individual variability in hepatocyte batches.

Central nervous system depression of neonates breastfed by mothers receiving oxycodone for postpartum analgesia

OBJECTIVE

To quantify the incidence of central nervous system (CNS) depression in neonates breastfed by mothers medicated with oxycodone as compared with neonates whose breastfeeding mothers used codeine or acetaminophen only.

STUDY DESIGN

We retrospectively compared 3 cohorts in 533 breastfeeding mother-infant pairs exposed to oxycodone (n = 139), codeine (n = 210), or acetaminophen only (n = 184). Standardized questionnaires were administered to mothers during the postpartum period to identify maternal and neonatal health outcomes temporally related to analgesia exposure.

RESULTS

Maternal exposure to oxycodone during breastfeeding was associated with a 20.1% rate of infant CNS depression (28/139) compared with 0.5% in the acetaminophen group (1/184; P < .0001; OR, 46.16; 95% CI, 6.2-344.2) and 16.7% in the codeine group (35/210; P > .05; OR, 0.79; 95% CI, 0.46-1.38). Mothers of neonates with symptoms in the oxycodone and codeine cohorts took significantly higher doses of medication compared with mothers of infants with no symptoms in the same cohorts (P = .0005 oxycodone; median, 0.4 mg/kg/day; range, 0.03-4.06 mg/kg/day versus median, 0.15 mg/kg/day; range, 0.02-2.25 mg/kg/day; codeine P < .001; median, 1.4 mg/kg/day; range, 0.7-10.5 mg/kg/day versus 0.9 mg/kg/day; range, 0.18-5.8 mg/kg/day). Mothers were significantly more likely to experience sedative adverse effects from oxycodone as compared with codeine (P < .0001; OR, 17.62; 95% CI, 9.95-31.21).

CONCLUSION

Oxycodone is not a safer alternative to codeine in breastfed infants.

Oxycodone controlled release in cancer pain management

Oral opioids are the treatment of choice for chronic cancer pain. Morphine is the strong opioid of choice for the treatment of moderate to severe cancer pain according to guidelines from the World Health Organization (WHO). This recommendation by the WHO was derived from availability, familiarity to clinicians, established effectiveness, simplicity of administration, and relative inexpensive cost. It was not based on proven therapeutic superiority over other options. Patients who experience inadequate pain relief or intolerable side effects with one opioid may often be successfully treated with another agent or with the same agent administered by a different route. Opioid rotation, or switching to an alternative opioid, helps some patients achieve better pain control with fewer associated adverse effects. Oxycodone is a μ-opioid receptor specific ligand, with clear agonist properties. It is an active potent opioid, which is in part a κ-receptor agonist. Like morphine and other pure agonists, there is no known ceiling to the analgesic effects of oxycodone. The active metabolites of oxycodone (eg, oxymorphone) could be important in oxycodone-mediated analgesia. The main pharmacokinetic difference between oxycodone and morphine is in oral bioavailability. The bioavailability of oxycodone is >60% and the bioavailability of morphine is 20%. Controlled-release oxycodone is absorbed in a bi-exponential fashion. There is a rapid phase with a mean half-life of 37 min, accounting for 38% of the dose, and a slow phase with a half-life of 6.2 h, which accounts for the residual 62%. Oxycodone elimination is impaired by renal failure because there are both an increased volume of distribution and reduced clearance. A lot of studies prove that the efficacy of controlled-release oxycodone in cancer-pain control is at least the same as morphine, immediate-release oxycodone and hydromorphone. Its toxicity profile seems better than that of morphine. There are actually several illustrations of a lower incidence of side-effects in the central nervous system. It is therefore possible to conclude that oxycodone represents a valid alternative to morphine in the management of moderate to severe cancer pain, also as first-line treatment.

Role of oxycodone and oxycodone/naloxone in cancer pain management

Oxycodone is a valued opioid analgesic, which may be administered either as the first strong opioid or when other strong opioids are ineffective. In case of insufficient analgesia and/or intense adverse effects such as sedation, hallucinations and nausea/vomiting a switch from another opioid to oxycodone might be beneficial. Oxycodone is administered to opioid-naive patients with severe pain and to patients who were unsuccessfully treated with weak opioids, namely tramadol, codeine and dihydrocodeine. Oxycodone effective analgesia may be attributed to its affinity to μ and possibly κ opioid receptors, rapid penetration through the blood-brain barrier and higher concentrations in brain than in plasma. Oxycodone displays high bioavailability after oral administration and may be better than morphine in patients with renal impairment due to the decreased production of active metabolites. Recently an oral controlled-release oxycodone formulation was introduced in Poland. Another new product that was launched recently is a combination of prolonged-release oxycodone with prolonged-release naloxone (oxycodone/naloxone tablets). The aim of this review is to outline the pharmacodynamic and pharmacokinetic properties, drug interactions, dosing rules, adverse effects, equianalgesic dose ratio with other opioids and clinical studies of oxycodone in patients with cancer pain. The potential role of oxycodone/naloxone in chronic pain management and its impact on the bowel function is also discussed.

Review of oral oxymorphone in the management of pain

Chronic cancer and nonmalignant pain (CNMP) is a common and major health problem afflicting approximately 40 million persons in the US. Most cancer patients, and many patients with CNMP, require opioid analgesics to obtain adequate pain relief. Oral oxymorphone is a new formulation of an existing parenteral opioid that has become available for the treatment of significant pain: acute postoperative, chronic arthritis, chronic low back, and chronic cancer pain. Oxymorphone is a typical mu-opioid agonist that is effective in both immediate- and extended-release (IR and ER) formulations. Oxymorphone is more lipid soluble than morphine, resulting in a rapid onset of action when given in tablet formulation, with a duration of action of approximately 4-6 hours in IR and 12 hours in ER preparations. Oxymorphone provides excellent pain relief for significant pain, with typical opioid side effects that are usually mild or moderate in intensity. Multiple double-blind, prospective, placebo-controlled clinical trials have demonstrated the clinical efficacy and safety of this new oral opioid preparation. Oral oxymorphone is an effective opioid that provides a new therapeutic option for the physician.

Pharmacological characterization of noroxymorphone as a new opioid for spinal analgesia

BACKGROUND

Noroxymorphone is one of the major metabolites of oxycodone. Although oxycodone is commonly used in the treatment of acute and chronic pain, little is known about the antinociceptive effects of noroxymorphone. We present an in vivo pharmacological characterization of noroxymorphone in rats.

METHODS

The antinociceptive properties of noroxymorphone were studied with thermal and mechanical models of nociception in rats.

RESULTS

Intrathecal noroxymorphone (1 and 5 microg/10 microL) induced a significantly longer lasting antinociceptive effect compared with oxycodone (200 microg/10 microL) and morphine (1 and 5 microg/10 microL). Pretreatment with subcutaneous naloxone (1 mg/kg) 15 min before intrathecal drug administration significantly decreased the antinociceptive effect of both noroxymorphone and morphine, indicating an opioid receptor-mediated antinociceptive effect. In the hotplate, paw pressure, and tail flick tests, subcutaneous noroxymorphone was inactive in doses of 5, 10, and 25 mg/kg. Also, no effect on motor function was observed in the rotarod test with doses studied. No antihyperalgesic effect was observed in the carrageenan model for inflammation in rats with subcutaneous noroxymorphone 25 mg/kg.

CONCLUSIONS

The results of this study indicate that noroxymorphone is a potent mu-opioid receptor agonist when administered intrathecally. The lack of systemic efficacy may indicate reduced ability of noroxymorphone to penetrate the blood-brain barrier due to its low calculated logD value (log octanol/water partition coefficient). Thus, noroxymorphone should have a negligible role in analgesia after systemic administration of oxycodone. Because of its spinal efficacy and long duration of effect, noroxymorphone is an interesting opioid for spinal analgesia with a low potential for abuse. Its safety for spinal administration should be assessed before clinical use.

Oxycodone as a component of multimodal analgesia for lactating mothers after Caesarean section: relationships between maternal plasma, breast milk and neonatal plasma levels

BACKGROUND

Oxycodone has become popular for post-Caesarean section (CS) analgesia yet it is not currently recommended for use in breast-feeding mothers because of limited information on its excretion into breast milk.

AIM

To investigate the relationship between maternal ingestion of oxycodone after CS and the resultant maternal plasma, breast milk and neonatal plasma drug levels up to 72-h post-partum.

METHODS

Fifty breast-feeding mothers taking oxycodone had blood and breast milk samples analysed for oxycodone levels at 24 h intervals after CS. Forty-one neonates had blood samples taken at 48 h.

RESULTS

Oxycodone was detected in the milk of mothers who had taken any dose in a 24-h period, with significant correlation between maternal plasma and milk levels (R(2) = 0.81). The median milk:plasma (M:P) ratio for the same period was 3.2:1. Over the subsequent 48 h, the relationship between plasma and milk levels was less strong (R(2) = 0.59) and there was a larger range of M:P levels with evidence of persistence of oxycodone in the breast milk of some mothers. Oxycodone levels up to 168 ng/mL were detected in breast milk (20% > 100 ng/mL). Oxycodone was detected in the plasma of one infant.

CONCLUSIONS

Oxycodone is concentrated in human breast milk up to 72-h post-partum. Breastfed infants may receive > 10% of a therapeutic infant dose. However, maternal oxycodone intake up to 72-h post-CS poses only minimal risk to the breast-feeding infant as low volumes of breast milk are ingested during this period.

Cerebral kinetics of oxycodone in conscious sheep

Oxycodone is an opioid analgesic that is administered orally or parenterally. The time-course of opioid action is a function of the systemic kinetics of the opioid, and the rate and extent of its entry into the brain and central nervous system. The latter is incompletely understood for oxycodone. Therefore, the cerebral kinetics of oxycodone was quantified using a conscious chronically instrumented sheep preparation. Five sheep were administered oxycodone as intravenous infusions (30 mg over 4 min). Using hybrid physiologically based kinetic models, cerebral kinetics was estimated from arterio-sagittal sinus concentration gradients and cerebral blood flow (CBF). A two-compartment membrane-limited model best described the data. The volume of the first brain compartment was 35.4 mL with a half-life of equilibrium of 0.6 min. The brain:blood equilibration of oxycodone was relatively slow (half-life of 7.2 min), with a large deep cerebral distribution volume (222.8 mL) for the second compartment and a moderate membrane permeability of 54.8 mL/min, which exceeded the nominal CBF (40 mL/min). Drug retention in the brain was 1.3% after 45 min. In conclusion, pharmacokinetic modelling of oxycodone showed a delayed equilibration between brain and blood of a nature that would be affected by changes in both CBF and blood brain barrier permeability.

Pharmacodynamics and pharmacokinetics of high-dose oxycodone infusion during and after coronary artery bypass grafting

OBJECTIVE

In small to moderate doses, oxycodone has similar analgesic efficacy to morphine with fewer side effects. The present study evaluated the pharmacokinetics and dynamics of high doses of oxycodone during anesthesia for primary coronary artery bypass grafting.

DESIGN

A randomized, prospective clinical evaluation.

SETTING

A major Scandinavian university clinic.

PARTICIPANTS

Two groups with 10 patients each were studied.

INTERVENTIONS

Invasive hemodynamics, echocardiograms, and electrocardiograms were monitored. Oxycodone kinetics, histamine liberation, and plasma cortisol levels were measured. Anesthesia was induced with 1.0 mg/kg of oxycodone and, thereafter, in a random order, maintained with a continuous infusion of oxycodone at a rate of either 0.5 mg/kg/h (group OX 0.5, 10 patients) or 1.0 mg/kg/h (group OX 1.0, 10 patients). An additional bolus dose of 0.5 mg/kg (OX 0.5) or 1.0 mg/kg (OX 1.0) of oxycodone was given before the incision. Enflurane was administered according to hemodynamic criteria.

MEASUREMENTS AND MAIN RESULTS

The induction of and the course of anesthesia were hemodynamically stable in all patients. Enflurane was given to every patient. The mean total doses of oxycodone were 3.5 mg/kg (OX 0.5) and 6.2 mg/kg (OX 1.0). The median t(1/2) of oxycodone varied from 5.1 to 5.9 hours. No hemodynamic differences were found between the groups. No histamine liberation was detected. During anesthesia, the predominant waves in the EEG were theta;- and delta-waves. The mean times to awakening were 3.8 hours and 7.0 hours in the groups OX 0.5 and 1.0, respectively. All patients were intubated until the first postoperative morning. No recall of awareness was reported.

CONCLUSION

A combination of oxycodone and enflurane provides hemodynamically stable anesthesia. No advantages were gained with the higher dose. Elimination of oxycodone was slower than reported previously.

Pharmacokinetics and tolerability of different doses of fentanyl following sublingual administration of a rapidly dissolving tablet to cancer patients: a new approach to treatment of incident pain

AIMS

It is estimated that two-thirds of cancer patients will at some point during their illness experience breakthrough pain. In this study, the pharmacokinetics of a novel sublingual dosage form of fentanyl developed for breakthrough pain was evaluated.

METHODS

Eleven Caucasian patients (seven male and 4 female, aged 34-75 years, median 60 years) with metastatic malignant disease were recruited initially, but three patients withdrew. Prior to the study all patients were on continuous nonfentanyl opiate medication. The study was a double-blind, cross-over trial, consisting of three 1-day treatment periods. A new rapidly dissolving preparation of fentanyl, was administered sublingually in single doses of 100, 200 and 400 microg, respectively, on three separate occasions. Plasma fentanyl concentrations were determined using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Pharmacokinetic parameters were calculated by noncompartment analysis. Tolerability and the occurrence of adverse events were monitored throughout the study by patient questionnaire.

RESULTS

The data from nine subjects who completed at least two periods were used in the analysis of variance. There were no significant differences between doses (100, 200 and 400 microg) for dose adjusted AUC (F = 0.42, P = 0.6660), dose adjusted C(max) (F = 0.08, P = 0.9206) and Tmax (F = 0.94, P = 0.4107). Thus, these parameters showed dose proportionality. The differences (400-100microg) in dose adjusted AUC from the three-period crossover analysis was -0.016 min.ng/ml (t = 0.71, P = 0.8718). Interindividual variability in systemic exposure to fentanyl was fairly small (25-40%), which may be related to a good in vivo biopharmaceutical performance of the sublingual tablet, and a relatively small fraction of the dose being swallowed. The first detectable plasma concentration of fentanyl was observed between 8 and 11 min after administration. t(max) increased from 39.7 +/- 17.4 to 48.7 +/- 26.3 and 56.7 +/- 24.6 min for the 100, 200 and 400 microg doses, respectively. Adverse events were few and did not increase with increasing dose.

CONCLUSION

With this rapidly dissolving fentanyl formulation, the first detectable plasma concentration of fentanyl was observed at 8-11 min after administration. The pharmacokinetics of the drug showed dose proportionately. This formulation of fentanyl seemed to be well tolerated by the patients.

Oxycodone

Oxycodone has been in clinical use since 1917. Parenteral oxycodone was used mainly for the treatment of acute postoperative pain whereas combinations, for example, oxycodone and acetaminophen, were used for moderate pain. Since the introduction of controlled-release oxycodone, it has been used to manage cancer-related pain and chronic non-cancer-related pain problems. Controlled studies have been performed in postoperative pain, cancer pain, osteoarthritis-related pain, and neuropathic pain due to postherpetic neuralgia and diabetic neuropathy. The pharmacodynamic effects of oxycodone are typical of a mu-opioid agonist. Oxycodone closely resembles morphine but it has some distinct differences, particularly in its pharmacokinetic profile. Being an old drug, the basic pharmacology of oxycodone has been a neglected field of research.

Epidural oxycodone or morphine following gynaecological surgery †

BACKGROUND

The analgesic action of oxycodone is of rapid onset, in contrast to morphine, and is mediated by kappa-opioid receptors of the spinal cord. We compared analgesia and side-effects of epidural oxycodone with those of morphine after gynaecological surgery.

METHODS

We studied prospectively in 75 women in a double-blind, randomized manner: epidural morphine 6 mg day(-1) (n=25), epidural oxycodone 6 mg day(-1) (n=25) and epidural oxycodone 12 mg day(-1) (n=25). All patients underwent gynaecological surgery under general (isoflurane and nitrous oxide) and epidural anaesthesia. Visual analogue scale (VAS) pain scores at rest and on coughing, verbal descriptive scale (VDS) satisfaction scores, sedation scores, pruritus scores and nausea/vomiting scores were recorded for 3 days after surgery.

RESULTS

VAS pain scores at rest in patients who received oxycodone 6 mg day(-1) were higher than in patients who received morphine 6 mg day(-1) at 6 h and on the first postoperative day and were significantly higher than in patients who received oxycodone 12 mg day(-1) on the first postoperative day. Scores for nausea, vomiting and pruritus in patients who received oxycodone 6 mg day(-1) and 12 mg day(-1) were lower than those in patients who received morphine. No significant differences were seen in VAS at cough and VDS satisfaction scores between the three groups.

CONCLUSION

Epidural oxycodone was as effective as morphine at the doses investigated, with fewer side-effects.

Demographics, assessment and management of pain in the elderly

The prevalence of pain increases with each decade of life. Pain in the elderly is distinctly different from pain experienced by younger individuals. Cancer is a leading cause of pain; however, other conditions that cause pain such as facet joint arthritis (causing low back pain), polymyalgia rheumatica, Paget's disease, neuropathies, peripheral vascular disease and coronary disease most commonly occur in patients over the age of 50 years. Poorly controlled pain in the elderly leads to cognitive failure, depression and mood disturbance and reduces activities of daily living. Barriers to pain management include a sense of fatalism, denial, the desire to be 'the good patient', geographical barriers and financial limitations. Aging causes physiological changes that alter the pharmacokinetics and pharmacodynamics of analgesics, narrowing their therapeutic index and increasing the risk of toxicity and drug-drug interactions. CNS changes lead to an increased risk of delirium. Assessment among the verbal but cognitively impaired elderly is satisfactorily accomplished with the help of unidimensional and multidimensional pain scales. A comprehensive physical examination and pain history is essential, as well as a review of cognitive function and activities of daily living. The goal of pain management among the elderly is improvement in pain and optimisation of activities of daily living, not complete eradication of pain nor the lowest possible drug dosages. Most successful management strategies combine pharmacological and nonpharmacological (home remedies, massage, topical agents, heat and cold packs and informal cognitive strategies) therapies. A basic principle of the pharmacological approach in the elderly is to start analgesics at low dosages and titrate slowly. The WHO's three-step guideline to pain management should guide prescribing. Opioid choices necessitate an understanding of pharmacology to ensure safe administration in end-organ failure and avoidance of drug interactions. Adjuvant analgesics are used to reduce opioid adverse effects or improve poorly controlled pain. Adjuvant analgesics (NSAIDs, tricyclic antidepressants and antiepileptic drugs) are initiated prior to opioids for nociceptive and neuropathic pain. Preferred adjuvants for nociceptive pain are short-acting paracetamol (acetaminophen), NSAIDs, cyclo-oxygenase-2 inhibitors and corticosteroids (short-term). Preferred drugs for neuropathic pain include desipramine, nortriptyline, gabapentin and valproic acid. Drugs to avoid are pentazocine, pethidine (meperidine), dextropropoxyphene and opioids that are both an agonist and antagonist, ketorolac, indomethacin, piroxicam, mefenamic acid, amitriptyline and doxepin. The type of pain, and renal and hepatic function, alter the preferred adjuvant and opioid choices. Selection of the appropriate analgesics is also influenced by versatility, polypharmacy, severity and type of pain, drug availability, associated symptoms and cost.

Palliative care and the child with cancer

There is a growing awareness and a WHO directive that the palliative care paradigm should be incorporated into the care of all children with cancer, irrespective of geographic location. The barriers to pediatric palliative care identified by pediatric oncologists [3] are lack of formal courses in pediatric palliative care, a high reliance on trial-and-error learning, lack of strong role models, and lack of access to a pain and palliative care service. These barriers must be overcome.

Cancer pain management in children

The World Health Organization document Cancer Pain Relief and Palliative Care in Children (WHO, 1998) advocates the global application of the principles of pain management and palliative care for children with cancer. The principles of pain management include the application of the WHO analgesic ladder, appropriate opioid dose escalation, the use of adjuvant analgesics, and the use of non-pharmacological methods of pain control. These principles of pain management should be incorporated into the treatment protocols of all children with cancer, acknowledging that treatment options may be limited for some children.