Pharmacokinetic-pharmacodynamic relationships of controlled-release oxycodone

Use of CYP2D6 Inhibitors with CYP2D6 Opioids: Association with Emergency Department Visits for Pain

Hydrocodone, tramadol, codeine, and oxycodone are commonly prescribed opioids that rely on activation by cytochrome P450 2D6 (CYP2D6). CYP2D6 inhibitors can significantly decrease CYP2D6 activity, leading to reduced generation of active metabolites, and impairing pain control. To understand this impact, we assessed emergency department (ED) visits in patients initiating these CYP2D6-dependent opioids while on CYP2D6-inhibitor antidepressants vs. antidepressants that do not inhibit CYP2D6. This retrospective cohort study included adult patients prescribed CYP2D6-dependent opioids utilizing electronic health records data from the University of Florida Health (2015-2021). The association between ED visits and inhibitor exposure was tested using multivariable logistic regression. The primary analysis had 12,118 patients (72% female; mean (SD) age, 55 (13.4)) in the hydrocodone/tramadol/codeine cohort and 5,547 patients (64% female; mean (SD) age, 53.6 (14.2)) in the oxycodone cohort. Hydrocodone/tramadol/codeine-treated patients exposed to CYP2D6-inhibitor antidepressants (n = 7,043) had a higher crude rate of pain-related ED visits than those taking other antidepressants (n = 5,075) (3.28% vs. 1.87%), with an adjusted odds ratio (aOR) of 1.75 (95% CI: 1.36 to 2.24). Similarly, in the oxycodone cohort, CYP2D6-inhibitor antidepressant-exposed individuals (n = 3,206) had a higher crude rate of ED visits than individuals exposed to other antidepressants (n = 2,341) (5.02% vs. 3.37%), with aOR of 1.70 (95% CI: 1.27-2.27). Similar findings were observed in secondary and sensitivity analyses. Our findings suggest patients with concomitant use of hydrocodone/tramadol/codeine or oxycodone and CYP2D6 inhibitors have more frequent ED visits for pain, which may be due to inadequate pain control.

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

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

Active Uptake of Oxycodone at Both the Blood-Cerebrospinal Fluid Barrier and The Blood-Brain Barrier without Sex Differences: A Rat Microdialysis Study

BACKGROUND

Oxycodone active uptake across the blood-brain barrier (BBB) is associated with the putative proton-coupled organic cation (H+/OC) antiporter system. Yet, the activity of this system at the blood-cerebrospinal fluid barrier (BCSFB) is not fully understood. Additionally, sex differences in systemic pharmacokinetics and pharmacodynamics of oxycodone has been reported, but whether the previous observations involve sex differences in the function of the H+/OC antiporter system remain unknown. The objective of this study was, therefore, to investigate the extent of oxycodone transport across the BBB and the BCSFB in female and male Sprague-Dawley rats using microdialysis.

METHODS

Microdialysis probes were implanted in the blood and two of the following brain locations: striatum and lateral ventricle or cisterna magna. Oxycodone was administered as an intravenous infusion, and dialysate, blood and brain were collected. Unbound partition coefficients (Kp,uu) were calculated to understand the extent of oxycodone transport across the blood-brain barriers. Non-compartmental analysis was conducted using Phoenix 64 WinNonlin. GraphPad Prism version 9.0.0 was used to perform t-tests, one-way and two-way analysis of variance followed by Tukey's or Šídák's multiple comparison tests. Differences were considered significant at p < 0.05.

RESULTS

The extent of transport at the BBB measured in striatum was 4.44 ± 1.02 (Kp,uu,STR), in the lateral ventricle 3.41 ± 0.74 (Kp,uu,LV) and in cisterna magna 2.68 ± 1.01 (Kp,uu,CM). These Kp,uu values indicate that the extent of oxycodone transport is significantly lower at the BCSFB compared with that at the BBB, but still confirm the presence of active uptake at both blood-brain interfaces. No significant sex differences were observed in neither the extent of oxycodone delivery to the brain, nor in the systemic pharmacokinetics of oxycodone.

CONCLUSIONS

The findings clearly show that active uptake is present at both the BCSFB and the BBB. Despite some underestimation of the extent of oxycodone delivery to the brain, CSF may be an acceptable surrogate of brain ISF for oxycodone, and potentially also other drugs actively transported into the brain via the H+/OC antiporter system.

Oxycodone: A Current Perspective on Its Pharmacology, Abuse, and Pharmacotherapeutic Developments

Oxycodone, a semisynthetic derivative of naturally occurring thebaine, an opioid alkaloid, has been available for more than 100 years. Although thebaine cannot be used therapeutically due to the occurrence of convulsions at higher doses, it has been converted to a number of other widely used compounds that include naloxone, naltrexone, buprenorphine, and oxycodone. Despite the early identification of oxycodone, it was not until the 1990s that clinical studies began to explore its analgesic efficacy. These studies were followed by the pursuit of several preclinical studies to examine the analgesic effects and abuse liability of oxycodone in laboratory animals and the subjective effects in human volunteers. For a number of years oxycodone was at the forefront of the opioid crisis, playing a significant role in contributing to opioid misuse and abuse, with suggestions that it led to transitioning to other opioids. Several concerns were expressed as early as the 1940s that oxycodone had significant abuse potential similar to heroin and morphine. Both animal and human abuse liability studies have confirmed, and in some cases amplified, these early warnings. Despite sharing a similar structure with morphine and pharmacological actions also mediated by the μ-opioid receptor, there are several differences in the pharmacology and neurobiology of oxycodone. The data that have emerged from the many efforts to analyze the pharmacological and molecular mechanism of oxycodone have generated considerable insight into its many actions, reviewed here, which, in turn, have provided new information on opioid receptor pharmacology. SIGNIFICANCE STATEMENT: Oxycodone, a μ-opioid receptor agonist, was synthesized in 1916 and introduced into clinical use in Germany in 1917. It has been studied extensively as a therapeutic analgesic for acute and chronic neuropathic pain as an alternative to morphine. Oxycodone emerged as a drug with widespread abuse. This article brings together an integrated, detailed review of the pharmacology of oxycodone, preclinical and clinical studies of pain and abuse, and recent advances to identify potential opioid analgesics without abuse liability.

Risk of Opioid Overdose Associated With Concomitant Use of Oxycodone and Selective Serotonin Reuptake Inhibitors

IMPORTANCE

Some selective serotonin reuptake inhibitors (SSRIs) inhibit the enzymes responsible for the metabolism of oxycodone, a potent prescription opioid. The clinical consequences of this interaction on the risk of opioid overdose have not been elucidated.

OBJECTIVE

To compare opioid overdose rates in patients initiating oxycodone while taking SSRIs that are potent inhibitors of the cytochrome-P450 2D6 enzyme (CYP2D6) vs SSRIs that are not.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study included adults who initiated oxycodone while receiving SSRI therapy between 2000 and 2020 whose data were included in 3 US health insurance databases.

EXPOSURES

Use of SSRIs that strongly inhibit CYP2D6 enzyme (fluoxetine or paroxetine) vs use of other SSRIs at the time of oxycodone initiation.

MAIN OUTCOMES AND MEASURES

Opioid overdose hospitalization or emergency department visit. Outcomes were assessed within 365 days of oxycodone initiation; in primary analyses, patients were followed up until the discontinuation of either oxycodone or their index SSRI group. Propensity score matching weights were used to adjust for confounding. Crude and weighted (adjusted) incidence rates and hazard ratios were estimated using Cox regression models, separately within each database and overall, stratifying on database.

RESULTS

A total of 2 037 490 initiated oxycodone while taking SSRIs (1 475 114 [72.4%] women; mean [SD] age, 50.1 [15.3] years). Most (1 418 712 [69.6%]) were receiving other SSRIs at the time of oxycodone initiation. In the primary analysis, we observed 1035 overdose events (0.05% of the study cohort). The adjusted incidence rate of opioid overdose in those using inhibiting SSRIs at the time of oxycodone initiation (9.47 per 1000 person-years) was higher than in those using other SSRIs (7.66 per 1000 person-years), indicating a greater risk of overdose among patients using CYP2D6-inhibiting SSRIs (adjusted hazard ratio, 1.23; 95% CI, 1.06-1.31). Results were consistent across multiple subgroup and sensitivity analyses.

CONCLUSIONS AND RELEVANCE

In this cohort study of US adults, initiating oxycodone in patients treated with paroxetine or fluoxetine was associated with a small increased risk of opioid overdose.

Sex and Estrous Cycle Differences in Analgesia and Brain Oxycodone Levels

Sex differences in opioid analgesia occur in rodents and humans, and could be due to differences in drug and metabolite levels. Thus, we investigated the sex and cycle differences in analgesia (nociception) from oxycodone in rats and related these to sex and cycle differences in brain and plasma oxycodone and metabolite levels. Since numerous opioids are CYP2D enzyme substrates and variation in CYP2D alters opioid drug levels and response, we also initiated studies to see if the sex and cycle differences observed might be due to differences in brain CYP2D activity. Across oxycodone doses, females in diestrus had higher analgesia (using tail flick latency) compared to males and females in estrus; we also demonstrated a direct effect of estrous cycle on analgesia within females. Consistent with the analgesia, females in diestrus had highest brain oxycodone levels (assessed using microdialysis) compared to males and females in estrus. Analgesia correlated with brain oxycodone, but not brain oxymorphone or noroxycodone levels, or plasma drug or metabolite levels. Propranolol (a CYP2D mechanism-based inhibitor), versus vehicle pre-treatments, increased brain oxycodone, and decreased brain oxymorphone/oxycodone drug level ratios (an in vivo CYP2D activity phenotype in the brain) in males and females in estrus, but not in females in diestrus. Brain oxymorphone/oxycodone inversely correlated with analgesia. Together, both sex and estrous cycle impact oxycodone analgesia and brain oxycodone levels, likely through regulation of brain CYP2D oxycodone metabolism. As CYP2D6 is expressed in human brain, perhaps similar sex and cycle influences also occur in humans.

Effect of Roux-en-Y gastric bypass on the pharmacokinetic-pharmacodynamic relationships of liquid and controlled-release formulations of oxycodone

The physiological changes following Roux-en-Y gastric bypass (RYGB) surgery may impact drug release from mechanistically different controlled-release tablets, making generic substitution inappropriate. This study aimed to characterise the pharmacokinetic-pharmacodynamic relationships of oxycodone from a lipid-based and water-swellable controlled-release tablet in RYGB patients. Twenty RYGB patients received 10-mg oral solution oxycodone or 20-mg controlled-release (water-swellable or lipid-based) oxycodone in a three-way, randomised, semiblinded and cross-over study. Blood sampling and pupillary recordings were conducted over a 24-h period. A previously established pharmacokinetic-pharmacodynamic model of these three formulations in healthy volunteers was used in the analysis as a reference model. No differences in absorption kinetics were seen between controlled-release formulations in patients. However, the absorption lag time was 11.5 min in patients vs 14 min in healthy volunteers for controlled-release tablets (P < 0.001). Furthermore, oral bioavailability was 14.4% higher in patients compared to healthy volunteers regardless of formulation type (P < 0.001). Oxycodone pharmacodynamics were not significantly affected by formulation or patient status. However, baseline pupil diameter was inversely correlated with age (P < 0.001) and plasma concentrations of oxycodone at half-maximum effect were 31% lower in males compared to females (P < 0.05). Generic substitution of monophasic lipid-based and water-swellable controlled-release oxycodone tablets may be considered safe in RYGB patients.

Oxycodone in the Opioid Epidemic: High 'Liking', 'Wanting', and Abuse Liability

It is estimated that nearly a third of people who abuse drugs started with prescription opioid medicines. Approximately, 11.5 million Americans used prescription drugs recreationally in 2016, and in 2018, 46,802 Americans died as the result of an opioid overdose, including prescription opioids, heroin, and illicitly manufactured fentanyl (National Institutes on Drug Abuse (2020) Opioid Overdose Crisis. https://www.drugabuse.gov/drugs-abuse/opioids/opioid-overdose-crisis . Accessed 06 June 2020). Yet physicians will continue to prescribe oral opioids for moderate-to-severe pain in the absence of alternative therapeutics, underscoring the importance in understanding how drug choice can influence detrimental outcomes. One of the opioid prescription medications that led to this crisis is oxycodone, where misuse of this drug has been rampant. Being one of the most highly prescribed opioid medications for treating moderate-to-severe pain as reflected in the skyrocketed increase in retail sales of 866% between 1997 and 2007, oxycodone was initially suggested to be less addictive than morphine. The false-claimed non-addictive formulation of oxycodone, OxyContin, further contributed to the opioid crisis. Abuse was often carried out by crushing the pills for immediate burst release, typically by nasal insufflation, or by liquefying the pills for intravenous injection. Here, we review oxycodone pharmacology and abuse liability as well as present the hypothesis that oxycodone may exhibit a unique pharmacology that contributes to its high likability and abuse susceptibility. We will discuss various mechanisms that likely contribute to the high abuse rate of oxycodone including clinical drug likability, pharmacokinetics, pharmacodynamics, differences in its actions within mesolimbic reward circuity compared to other opioids, and the possibility of differential molecular and cellular receptor interactions that contribute to its selective effects. We will also discuss marketing strategies and drug difference that likely contributes to the oxycodone opioid use disorders and addiction.

Oxycodone Concentrations and Metabolic Ratios in Femoral Blood from Fatal Intoxications and Other Causes of Death using LC-MS-MS

Oxycodone (OC) is an opioid with strong analgesic effects widely used to treat acute and chronic pain. Interpretation of OC concentrations in postmortem cases is complicated due to tolerance and overlapping concentrations for fatal and non-fatal levels. In this study, our aim was to develop and validate a method for OC and its three metabolites: noroxycodone (NOC), oxymorphone (OM) and noroxymorphone (NOM) in postmortem femoral blood. Our goal was to define reference concentrations for intoxications and non-intoxications and investigate metabolic ratios in different causes of death. A rapid LC-MS-MS method using protein-precipitated postmortem blood was developed. Lower limit of quantitation was 0.005 μg/g blood for all analytes; upper limit of quantitation was 1.0 μg/g for OC and NOC and 0.25 μg/g for OM and NOM. The method displayed high precision (3.3-7.7%) and low bias (-0.3 to 12%). In total, 192 cases were analyzed and concentrations ranged from 0.005 to 13 μg/g for OC, 0.005 to 2.0 μg/g for NOC, 0.005 to 0.24 μg/g for OM, and 0.005 to 0.075 μg/g for NOM. We found a significant difference in OC concentration between the cases where OC contributed and those where it did not. In spite of that, we do not recommend the use of a specific blood concentration to distinguish fatal intoxications. Instead, the percentiles from our data set suggest that concentrations >0.2 μg/g are likely to have contributed to toxicity, but that concentrations as high as 0.3 might be tolerated without toxic effects. In addition, we also found that a low NOC/OC ratio could point toward an acute fatal intoxication. In conclusion, the OC concentration alone may not be sufficient to diagnose a fatal intoxication.

Oxycodone self-administration and withdrawal behaviors in male and female Wistar rats

RATIONALE

Over the last decade, oxycodone has become one of the most widely abused drugs in the USA. Oxycodone use disorder (OUD) is a serious health problem that has prompted a need to develop animal models of OUD that have both face and predictive validity. Oxycodone use in humans is more prevalent in women and leads to pronounced hyperalgesia and irritability during withdrawal. However, unclear is whether current animal models of oxycodone self-administration recapitulate these characteristics in humans.

OBJECTIVES

We assessed the face validity of a model of extended-access oxycodone self-administration in rats by examining the escalation of oxycodone intake and behavioral symptoms of withdrawal, including irritability-like behavior and mechanical nociception, in male and female Wistar rats.

RESULTS

Both male and female rats escalated their oxycodone intake over fourteen 12-h self-administration sessions. After escalation, female rats administered more drug than male rats. No differences in plasma oxycodone levels were identified, but males had a significantly higher level of oxycodone in the brain at 30 min. Extended access to oxycodone significantly decreased aggressive-like behavior and increased defensive-like behaviors when tested immediately after a 12-h self-administration session, followed by a rebound increase in aggressive-like behavior 12 h into withdrawal. Tests of mechanical nociception thresholds during withdrawal indicated pronounced hyperalgesia. No sex differences in irritability-like behavior or pain sensitivity were observed.

CONCLUSIONS

The present study demonstrated the face validity of the extended access model of oxycodone self-administration by identifying sex differences in the escalation of oxycodone intake and pronounced changes in pain and affective states.

Challenges and innovations of drug delivery in older age

Both drug delivery performance and various age-related physical, mental and physiological changes can affect drug effectiveness and safety in elderly patients. The many drug delivery systems developed over the years include recent novel transdermal, nasal, pulmonary and orally disintegrating tablets that provide consistent, precise, timely and more targeted drug delivery. Certain drug delivery systems may be associated with suboptimal outcomes in the elderly because of the nature of drug present, a lack of appreciation of the impact of age-related changes in drug absorption, distribution and clearance, the limited availability of pharmacokinetic, safety and clinical data. Polypharmacy, patient morbidity and poor adherence can also contribute to sub-optimal drug delivery systems outcomes in the elderly. The development of drug delivery systems for the elderly is a poorly realised opportunity, with each system having specific advantages and limitations. A key challenge is to provide the innovation that best meets the specific physiological, psychological and multiple drug requirements of individual elderly patients.

Pain Management in Pediatric Chronic Kidney Disease

Pain is a common problem in children with chronic kidney disease (CKD); however, limited data exist regarding its management. Although most pain is managed pharmacologically, in some instances non-pharmacologic management can aid in safely ameliorating discomfort. Because of the accumulation of toxic metabolites, many common pain medications have adverse effects on kidney function or altered pharmacokinetics in the setting of CKD. Decreased clearance impacts safe dosing of analgesics. The pain management of patients on renal replacement therapy requires an understanding of drug clearance due to the different modalities of dialysis. This educational review highlights pain medications that are safe, albeit often with adjusted dosing, as well as drugs best avoided in the management of pediatric kidney disease. Acetaminophen should be used as a first-line therapy for pain management in children with CKD. Opioids may be added to control moderate to severe pain. Although data are currently lacking, buprenorphine holds promise as a potentially useful drug for the treatment of pain in pediatric patients with CKD. The addition of adjuvant pain medications and non-pharmacologic therapies maybe also be helpful. Despite these options, pain often remains difficult to treat in children with CKD.

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.

Gender difference in prescription opioid abuse: A focus on oxycodone and hydrocodone

Several data gathered in the last decade indicate an increase of abuse of prescription opioid drugs oxycodone (OXY) and hydrocodone (HYDRO) in women. However, to date there are no conclusive evidences investigating the gender-dependent abuse liability of prescription opioids. This study aims to supply a specific focus on women's data through a selective summary of the literature analyzing gender differences in the pharmacokinetic and pharmacodynamic dimension of OXY and HYDRO. Findings from this study suggest that the majority of OXY and HYDRO pharmacokinetic and pharmacodynamic effects do not differ according to gender, though confirming a significant difference in the incidence of adverse effects as demonstrated by the increased gastrointestinal adverse reactions in female subjects. Although the majority of recent clinical studies include an equal number of female and male subjects, the main outcome parameters do not relate specifically to gender differences. Due to the gender influence in activity of CYP3A4 and its crucial role in metabolism of both OXY than HYDRO, we suggest that assessing pharmacokinetic and pharmacodynamic interactions in clinical studies may be useful to clarify the effect of the higher CYP3A4 activity in female in relation to CYP2D6 genotype. Overall, considering the paucity of data regarding gender differences in European Union, this work highlights that impact of new abuse deterrent formulations should be assessed with a special focus on data concerning female subjects.

Pooled post hoc analysis of population pharmacokinetics of oxycodone and acetaminophen following a single oral dose of biphasic immediate-release/extended-release oxycodone/acetaminophen tablets

This analysis evaluated the single-dose population pharmacokinetics (PK) of biphasic immediate-release (IR)/extended-release (ER) oxycodone (OC)/acetaminophen (APAP) 7.5/325 mg tablets administered under fasted conditions and the effects of a meal on their single-dose population PK. Data were pooled from four randomized, single-dose crossover trials enrolling healthy adult (18–55 years old) participants (three trials) and nondependent recreational users of prescription opioids (one trial) with a body weight of ≥59 kg. Participants received IR/ER OC/APAP 7.5/325 mg tablets in single doses of 7.5/325 mg (one tablet), 15/650 mg (two tablets), or 30/1,300 mg (four tablets) under fasted or fed conditions. Six variables were examined: sex, race, age, weight, height, and body mass index. Single-dose population PK was analyzed using first-order conditional estimation methods. A total of 151 participants were included in the analysis under fasted conditions, and 31 participants were included in the fed analysis. Under fasted conditions, a 10% change in body weight was accompanied by ~7.5% change in total body clearance (CL/F) and volume of distribution (V/F) of OC and APAP. Black participants had 17.3% lower CL/F and a 16.9% lower V/F of OC compared with white participants. Under fed conditions, the absorption rate constant of OC and APAP decreased significantly, although there was no effect on CL/F and V/F. Considering that the recommended dose for IR/ER OC/APAP 7.5/325 mg tablets is two tablets every 12 hours, adjustments of <50% are not clinically relevant. Dose adjustment may be necessary for large deviations from average body weight, but the small PK effects associated with race and consumption of a meal are not clinically relevant.

Pharmacokinetics of oxycodone after intravenous and subcutaneous administration in Japanese patients with cancer pain

ABSTRACT In Japan, Oxycodone hydrochloride injection formulation has been approved in 2012. However, its pharmacokinetics has been poorly studied. The aim of this study is to evaluate the pharmacokinetics of oxycodone after intravenous and subcutaneous administration of oxycodone hydrochloride injection in Japanese patients with cancer pain. Noncompartmental analysis and population pharmacokinetic analysis were performed. We conducted a multicenter open-label study of oxycodone hydrochloride administered as constant infusion with the dose titrated individually according to the pain intensity in patients with cancer pain. Pharmacokinetic parameters for plasma oxycodone and its metabolites were estimated using pharmacokinetics of oxycodone was evaluated using a total of 344 plasma concentrations obtained from 89 patients. The estimated geometric mean clearance (CL) of oxycodone was 24.3 L per hour after constant intravenous infusion and 29.5 L per hour after constant subcutaneous infusion, respectively. Population pharmacokinetic analysis indicated that body surface area was the influencing factor on CL and there were no pharmacokinetic differences for CL between intravenous and subcutaneous infusion. These results provide important information for the clinical use of oxycodone injection.

Contribution of oxycodone and its metabolites to the overall analgesic effect after oxycodone administration

OBJECTIVE

Oxycodone (OC) is an opioid which exerts its analgesic effect through µ-receptors in the brain. It is metabolized through CYP450 enzymes and some of the metabolites show pharmacological activity. The aim of this investigation is to research the contribution of the metabolites of OC to its overall analgesic effect. A further aim was to elucidate the role of drug-drug interactions and CYP2D6 polymorphism.

RESEARCH DESIGN AND METHODS

The authors performed a literature search to identify published information on: blood concentrations of OC and metabolites, protein binding, blood-brain-barrier behavior and opioid receptor affinity. The authors then calculated the contribution of OC and metabolites to the overall analgesic effect.

RESULTS

OC itself is responsible for 83.02 and 94.76% of the analgesic effect during p.o. and i.v. administration, respectively. Oxymorphone (OM), which has a much higher affinity for the µ-receptor, only plays a minor role (15.77 and 4.52% for p.o. and i.v., respectively). Although the CYP2D6 genotype modulates OM pharmacokinetics, OC remains the major contributor to the overall analgesic effect.

CONCLUSION

This article's calculations demonstrate that OC itself is responsible for the analgesic effect. Although OM and noroxymorphone have much higher µ-receptor affinity than the parent drug, the metabolite concentrations at the site of action are very low. This suggests that there is a minimal analgesic effect from these metabolites.

Double-Blind, Randomized Comparison of the Analgesic and Pharmacokinetic Profiles of Controlled- and Immediate-Release Oral Oxycodone in Cancer Pain Patients

Thirty patients with cancer pain completed a double-blind crossover study comparing controlled-release (CR) and immediate-release (IR) oxycodone. In open-label titration (2 to 21 days), these patients were stabilized on IR oxycodone qid. They were then randomized to double-blind treatment with CR oxycodone q12h or IR oxycodone qid for 3 to 7 days followed by crossover at the same daily dose. Mean (+/- SD) pain intensity (0 = none to 10 = severe) decreased from a baseline of 6.0 +/- 2.2 to 2.7 +/- 1.1 after titration with IR oxycodone dosed qid. Pain intensity remained stable throughout double-blind treatment: 2.7 +/- 1.9 with CR oxycodone and 2.8 +/- 1.9 with IR oxycodone. Acceptability of therapy and pain scores correlated with plasma oxycodone concentrations for each interval and were similar for both medications (IR and CR oxycodone). Adverse events were similar for both formulations. Following repeat dosing under double-blind conditions, oral CR oxycodone administered q12h provided analgesia comparable to IR oxycodone given qid.

Oxymorphone active uptake at the blood-brain barrier and population modeling of its pharmacokinetic-pharmacodynamic relationship

The aim of this study was to characterize the blood-brain barrier (BBB) transport and pharmacokinetics-pharmacodynamics (PKPD) relationship of oxymorphone and to further elucidate its possible contribution to oxycodone analgesia. The BBB transport of oxymorphone was studied using microdialysis in male Sprague-Dawley rats. Samples from microdialysis blood and brain probes, brain tissue, and plasma were analyzed by liquid chromatography with tandem mass spectrometry. The effect was measured as tail-flick latency. The study consisted of a PKPD experiment with combined microdialysis and antinociceptive measurements (n = 8), and another antinociceptive effect experiment (n = 9) using a 10 times lower dose. The combined data were analyzed with an integrated PKPD model in nonlinear mixed effect modeling utilizing a specific method (M3) for handling missing PD observations. The concentration of unbound oxymorphone was higher in brain than in blood, with a ratio of 1.9 (RSE, 9.7%), indicating active uptake at the BBB. The integrated PKPD model described the oxymorphone BBB transport and PKPD relationship successfully, with an EC50 in the brain of 63 ng/mL, and the M3 method was able to address the issue of censored observations. Oxymorphone has active uptake transport at the BBB in rats, with moderate uptake clearance to the brain. Its contribution to analgesia after oxycodone administration is not significant.

Management of acute and post-operative pain in chronic kidney disease

Chronic kidney disease is common and patients with many co-morbid conditions frequently have to undergo surgical procedures and, therefore, require effective pain management. The pharmacokinetics of various analgesic agents are not well studied in patients with chronic kidney disease and the risk of accumulation of the main drug or their metabolites, resulting in serious adverse events, is a common scenario on medical and surgical wards. It is common for these patients to be cared for by 'non-nephrologists' who often prescribe the standard dose of the commonly used analgesics, without taking into consideration the patient's kidney function. It is important to recognize the problems and complications associated with the use of standard doses of analgesics, and highlight the importance of adjusting analgesic dosage based on kidney function to avoid complications while still providing adequate pain relief.

Management of acute and post-operative pain in chronic kidney disease

Chronic kidney disease is common and patients with many co-morbid conditions frequently have to undergo surgical procedures and, therefore, require effective pain management. The pharmacokinetics of various analgesic agents are not well studied in patients with chronic kidney disease and the risk of accumulation of the main drug or their metabolites, resulting in serious adverse events, is a common scenario on medical and surgical wards. It is common for these patients to be cared for by 'non-nephrologists' who often prescribe the standard dose of the commonly used analgesics, without taking into consideration the patient's kidney function. It is important to recognize the problems and complications associated with the use of standard doses of analgesics, and highlight the importance of adjusting analgesic dosage based on kidney function to avoid complications while still providing adequate pain relief.

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.

Controlled-release oxycodone compared with controlled-release morphine in the treatment of cancer pain: A randomized, double-blind, parallel-group study

Controlled-release oral formulations of oxycodone and morphine are both suitable analgesics for moderate to severe pain. They were compared in cancer-pain patients randomized to double-blind treatment with controlled-release oxycodone (n = 48) or controlled-release morphine (n = 52) every 12 h for up to 12 days. Stable analgesia was achieved by 83% of controlled-release oxycodone and 81% of controlled-release morphine patients in 2 days (median). Following titration to stable analgesia, pain intensity (0=none to 3=severe) decreased from baseline within each group (p </= 0.005), from 1.9 (0.1) to 1.3 (0.1), mean (SE), with controlled-release oxycodone, and from 1.6 (0.1) to 1.0 (0.1) with controlled-release morphine (no significant between-group differences). Typical opioid adverse experiences were reported in both groups. Hallucinations were reported only with controlled-release morphine (n = 2). Visual analog scores (VAS) for 'itchy' and 'scratchin' were lower with controlled-release oxycodone (p </= 0.044), as was peak-to-trough fluctuation in steady-state plasma concentration (p = 0.004). The correlation between plasma concentration and dose was stronger (p = 0.026) for oxycodone (0.7) than morphine (0.3). The relationship between pain intensity (VAS) and plasma concentration was more positive for oxycodone (p = 0.046). There was a positive relationship between morphine-6-glucuronide concentrations and urea nitrogen and creatinine levels (p = 0.001). Controlled-release oxycodone was as effective as controlled-release morphine in relieving chronic cancer-related pain, and as easily titrated to the individual's need for pain control. While adverse experiences were similar, controlled-release oxycodone was associated with less itching and no hallucinations. Controlled-release oxycodone provides a rational alternative to controlled-release morphine for the management of moderate to severe cancer-related pain.

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.

Inhibition of cytochrome P450 3A by clarithromycin uniformly affects the pharmacokinetics and pharmacodynamics of oxycodone in young and elderly volunteers

The aim of this study was to investigate the effect of the cytochrome P450 3A4 inhibitor clarithromycin on the pharmacokinetics and pharmacodynamics of oral oxycodone in young and elderly subjects. Ten young and 10 elderly healthy subjects participated in this placebo-controlled, randomized, 2-phase crossover study. Subjects took clarithromycin 500 mg or placebo twice daily for 5 days. On day 4, subjects ingested an oral dose of 10 mg oxycodone. Plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 hours, and pharmacological response for 12 hours. Clarithromycin decreased the apparent clearance of oxycodone by 53% in young and 48% in elderly subjects (P < 0.001) and prolonged its elimination half-life. The mean area under the plasma concentration-time curve (AUC0-∞) of oxycodone was increased by 2.0-fold (range, 1.3-fold to 2.7-fold) (P < 0.001) in young and 2.3-fold (range, 1.1-fold to 3.8-fold) (P < 0.001) in elderly subjects. The formation of noroxycodone was decreased by 74% in young and 71% in elderly subjects (P < 0.001). The ratio of AUC0-∞ of oxycodone during the clarithromycin phase compared with the one with placebo did not differ between the age groups. Clarithromycin did not alter the pharmacological response to oxycodone. Clarithromycin increased the exposure to oral oxycodone, but the magnitude of this effect was not age related. Although the pharmacological response to oxycodone was not significantly influenced by clarithromycin, dose reductions may be necessary in the most sensitive patients to avoid adverse effects when oxycodone is used concomitantly with clarithromycin.

Clinical pharmacology of analgesic medicines in older people: impact of frailty and cognitive impairment

Pain is highly prevalent in frail older people who often have multiple co-morbidities and multiple medicines. Rational prescribing of analgesics in frail older people is complex due to heterogeneity in drug disposition, comorbid medical conditions, polypharmacy and variability in analgesic response in this population. A critical issue in managing older people with pain is the need for judicious choice of analgesics based on a comprehensive medical and medication history. Care is needed in the selection of analgesic medicine to avoid drug-drug or drug-disease interactions. People living with dementia and cognitive impairment have suboptimal pain relief which in part may be related to altered pharmacodynamics of analgesics and challenges in the systematic assessment of pain intensity in this patient group. In the absence of rigorously controlled trials in frail older people and those with cognitive impairment a pharmacologically-guided approach can be used to optimize pain management which requires a systematic understanding of the pharmacokinetics and pharmacodynamics of analgesics in frail older people with or without changes in cognition.

Exposure to oral oxycodone is increased by concomitant inhibition of CYP2D6 and 3A4 pathways, but not by inhibition of CYP2D6 alone

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Oxycodone is an opioid analgesic that is metabolized mainly in the liver by cytochrome P450 (CYP) 2D6 and 3A4 enzymes. So far, the effects of CYP2D6 or CYP3A4 inhibitors on the pharmacokinetics of oxycodone in humans have not been systematically studied.

WHAT THIS STUDY ADDS

Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone. When both of CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially.

AIM

The aim of this study was to find out whether the inhibition of cytochrome P450 2D6 (CYP2D6) with paroxetine or concomitant inhibition of CYP2D6 and CYP3A4 with paroxetine and itraconazole, altered the pharmacokinetics and pharmacological response of orally administered oxycodone.

METHODS

A randomized placebo-controlled cross-over study design with three phases was used. Eleven healthy subjects ingested 10 mg of oral immediate release oxycodone on the fourth day of pre-treatment with either placebo, paroxetine (20 mg once daily) or paroxetine (20 mg once daily) and itraconazole (200 mg once daily) for 5 days. The plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 h, and pharmacological (analgesic and behavioural) effects were evaluated.

RESULTS

Paroxetine alone reduced the area under concentration-time curve (AUC(0,0-48 h)) of the CYP2D6 dependent metabolite oxymorphone by 44% (P < 0.05), but had no significant effects on the plasma concentrations of oxycodone or its pharmacological effects when compared with the placebo phase. When both oxidative pathways of the metabolism of oxycodone were inhibited with paroxetine and itraconazole, the mean AUC(0,infinity) of oxycodone increased by 2.9-fold (P < 0.001), and its C(max) by 1.8-fold (P < 0.001). Visual analogue scores for subjective drug effects, drowsiness and deterioration of performance were slightly increased (P < 0.05) after paroxetine + itraconazole pre-treatment when compared with placebo.

CONCLUSIONS

Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone if the function of the CYP3A4 pathway is normal. When both CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially.

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.

CYP3A5*3 affects plasma disposition of noroxycodone and dose escalation in cancer patients receiving oxycodone

The aim of this study was to evaluate the plasma dispositions of oxycodone and its demethylates and dose escalation based on genetic polymorphisms of CYP2D6, CYP3A5, ABCB1, and OPRM1 in cancer patients receiving oxycodone. Sixty-two Japanese cancer patients receiving oxycodone extended-release tablets were enrolled. Predose plasma concentrations (C(12)) of oxycodone, noroxycodone, and oxymorphone were determined at the titrated dose. Daily oxycodone escalation rate was evaluated as the opioid escalation index (OEI). Genetic variants did not significantly alter oxycodone C(12). Oxymorphone C(12) and its ratio to oxycodone C(12) were significantly higher in CYP2D6 extensive metabolizers than in intermediate metabolizers but did not affect dose escalation. In contrast, noroxycodone C(12) and its ratio to oxycodone C(12) were significantly higher in the CYP3A5*1 carrier group than in the *3/*3 group. The OEI was significantly higher in the CYP3A5*3/*3 group than in the *1 carrier group. No significant difference was observed in the OEI in the other genetic variants. Noroxycodone C(12) was higher in the dose escalation group as compared to the nonescalation group and significantly affected the incidence of dose escalation. In conclusion, CYP3A5*3 altered the plasma disposition of noroxycodone, which was inversely affecting the dose escalation in cancer patients receiving oxycodone.

Influences on the pharmacokinetics of oxycodone: a multicentre cross-sectional study in 439 adult cancer patients

Objective

Oxycodone is widely used for the treatment of cancer pain, but little is known of its pharmacokinetics in cancer pain patients. The aim of this study was to explore the relationships between ordinary patient characteristics and serum concentrations of oxycodone and the ratios noroxycodone or oxymorphone/oxycodone in cancer patients.

Methods

Four hundred and thirty-nine patients using oral oxycodone for cancer pain were included. The patients’ characteristics (sex, age, body mass index [BMI], Karnofsky performance status, “time since starting opioids”, “oxycodone total daily dose”, “time from last oxycodone dose”, use of CYP3A4 inducer/inhibitor, “use of systemic steroids”, “number of medications taken in the last 24 h”, glomerular filtration rate (GFR) and albumin serum concentrations) influence on oxycodone serum concentrations or metabolite/oxycodone ratios were explored by multiple regression analyses.

Results

Sex, CYP3A4 inducers/inhibitors, total daily dose, and “time from last oxycodone dose” predicted oxycodone concentrations. CYP3A4 inducers, total daily dose, and “number of medications taken in the last 24 h” predicted the oxymorphone/oxycodone ratio. Total daily dose, “time from last dose to blood sample”, albumin, sex, CYP3A4 inducers/inhibitors, steroids, BMI and GFR predicted the noroxycodone/oxycodone ratio.

Conclusion

Women had lower oxycodone serum concentrations than men. CYP3A4 inducers/inhibitors should be used with caution as these are predicted to have a significant impact on oxycodone pharmacokinetics. Other characteristics explained only minor parts of the variability of the outcomes.