Functional bias of morphine and oliceridine under conditions of minor injury.

Recent reports suggest pain from surgical injury may influence the risks associated with exposure to opioids. In mice, hind-paw incision attenuates morphine-primed reinstatement due to kappa opioid receptor activation by dynorphin. In this focused group of studies, we examined the hypotheses that kappa-opioid receptor activation in the nucleus accumbens mediates attenuated drug- primed reinstatement after incisional surgery, and the G-protein biased mu-opioid agonist, oliceridine, leads to less priming of the dynorphin effect in comparison to morphine. To address these hypotheses, adult C57BL/6 male mice underwent intracranial cannulation for administration of the selective kappa-opioid antagonist norBNI directly into the nucleus accumbens. After recovery, they were conditioned with morphine or oliceridine after hind-paw incisional injury, then underwent extinction followed by opioid-primed reinstatement. Intra-accumbal administration of norBNI was carried out prior to testing. The nucleus accumbens and medial prefrontal cortex were extracted and analyzed for expression of prodynorphin. We observed that animals conditioned with morphine in the setting of incisional injury demonstrated blunted responses to opioid-primed reinstatement, and that the blunted responses were reversed with intra-accumbal norBNI administration. Persistently elevated levels of prodynorphin expression in the medial prefrontal cortex and nucleus accumbens were observed in the incised morphine-treated animals. However, both behavioral and molecular changes were absent in animals with incisional injury conditioned with oliceridine. These findings suggest a role for prodynorphin expression in the nucleus accumbens with exposure to morphine after surgery that may protect individuals from relapse not shared with biased mu- opioid receptor agonists.

Further investigation of the rapid-onset and short-duration action of the G protein-biased µ-ligand oliceridine.

TRV130 (oliceridine), a G protein-biased ligand for µ-opioid receptor, has recently been synthesized. It is considered to have strong antinociceptive effects and only minor adverse effects. However, whether or not oliceridine actually exhibits an ideal pharmacological profile as an analgesic has not yet been fully clarified in animal studies. This study examined the pharmacological profile of oliceridine in cells and animals. Oliceridine (10 µM) did not produce any µ-opioid receptor internalization in cells even though it increased impedance, which reflects the activation of Gi protein using the CellKey™ system, and inhibited the formation of cAMP. In mice, oliceridine (0.3-10 mg/kg) produced a dose-dependent antinociceptive effect with a rapid-onset and short-duration action in the hot-plate test, as well as antihyperalgesia after sciatic nerve ligation without the development of antinociceptive tolerance using the thermal hyperalgesia test. On the other hand, oliceridine inhibited gastrointestinal transit. Furthermore, oliceridine produced rapid-onset hyperlocomotion at antinociceptive doses; sensitization developed in mice and an emetic effect was observed in ferrets. These results indicate that, although oliceridine may produce dopamine-related behaviors even through selective stimulation of the G-protein-biased µ-opioid receptor pathway, it still offers advantages for breakthrough pain without antinociceptive tolerance with adequate doses.

Oliceridine for the Management of Acute Postoperative Pain.

OBJECTIVE: To review the pharmacological characteristics, clinical evidence, and place in the management of acute postoperative pain severe enough to require an intravenous opioid. DATA SOURCES: A comprehensive literature search was conducted in PubMed (January 2000 to December 1, 2020). Key search terms included oliceridine or acute postoperative pain. Other sources were derived from product labeling and ClinicalTrials.gov. STUDY SELECTION AND DATA EXTRACTION: All English-language articles identified from the data sources were reviewed and evaluated. Phase I, II, and III clinical trials were included. DATA SYNTHESIS: Oliceridine is a novel selective µ-receptor G-protein pathway modulator. It has the property of activating G-protein signaling while causing low ß-arrestin recruitment to the µ-receptor. Intravenous oliceridine showed statistically superior analgesia than placebo in patients with moderate or severe pain after surgery, with a favorable safety and tolerability profile regarding respiratory and gastrointestinal adverse effects, compared with morphine. RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE: The analgesic capacity of oliceridine is at least comparable to that of morphine at clinically relevant dosages, with a rapid onset of action. Also, it may be associated with a lower incidence of adverse events at dosing regimens associated with comparable analgesia. These data suggest that oliceridine may provide an important new treatment option for the management of moderate to severe postoperative pain where an intravenous opioid is warranted. CONCLUSION: Oliceridine has obvious analgesic effects in patients with moderate or severe pain after surgery; additionally, it has a favorable safety and tolerability profile.

Recent Developments in Drugs for GI Endoscopy Sedation.

Providing sedation for patients undergoing gastrointestinal (GI) endoscopy continues to be a debated topic in both anesthesia and gastroenterology circles. Sedation approaches are widely varied across the globe. While propofol administration is embraced by more endoscopists and patients, its administration evolves controversy. Whereas trained nurses and gastroenterologists are allowed to administer propofol for GI endoscopy sedation in Europe and Asia, it is the sole privilege of anesthesia providers in the USA. However, the costs of anesthesia providers are significant and threaten to derail the screening colonoscopy practice. Efforts were made by both drug and device manufacturers to find alternatives. Fospropofol was one such effort that did not live up to the expectations due to respiratory depressant properties that were similar to propofol. Use of a new tool to administer propofol in the form of Sedasys® was the next experiment that tried to find alternative to anesthesia providers. The device did not succeed due to inadequate sedation. The latest effort is remimazolam, a new benzodiazepine that has quicker recovery profile. In the interim, many drug combinations such as propofol-dexmedetomidine and propofol-ketamine are improving the safety without compromising the quality of sedation. This review attempts to discuss the new drug innovations and drug combinations of existing sedatives for the benefit of readers.

Medical, Political, and Economic Considerations for the Use of MAC for Endoscopic Sedation: Big Price, Little Justification?

The last few decades of gastrointestinal (GI) endoscopy have seen phenomenal growth. In many aspects, GI endoscopy has led the field of nonsurgical interventional medicine. In many aspects, this growth is facilitated by advancements in sedation-both drugs and techniques. Unfortunately, the topic of GI endoscopy sedation is also mired in many controversies, mainly emanating from the cost of anesthesia providers. While no one debates their role in the majority of advanced endoscopic procedures, the practice of universal propofol sedation in the USA, delivered by anesthesia providers, needs a closer look. In this review, medical, political, and economic considerations of this important topic are discussed in a very frank and honest way. While such ubiquitous propofol use has increased satisfaction of both patients and gastroenterologists, there is little justification. More importantly, going by the evidence, there is even less justification for the mandated anesthesia providers use for such delivery. Unfortunately, the FDA could not be convinced otherwise. The new drug fospropofol met the same fate. Approval of SEDASYS®, the first computer-assisted personalized sedation system, was a step in the right direction, nevertheless an insufficient step that failed to takeoff. As a result, in spite of years of research and efforts of many august societies, the logjam of balancing cost and justification of propofol sedation has continued. We hope that recent approval of remimazolam, a novel benzodiazepine, and potential approval of oliceridine, a novel short-acting opioid, might be able to contain the cost without compromising the quality of sedation.

The Utilization of Mu-Opioid Receptor Biased Agonists: Oliceridine, an Opioid Analgesic with Reduced Adverse Effects.

PURPOSE OF REVIEW: The purpose of this review is to summarize the current understanding of opioid pathways in mediating and/or modulating analgesia and adverse effects. Oliceridine is highlighted as a novel mu-opioid receptor agonist with selective activation of G protein and ß-arrestin signaling pathways. RECENT FINDINGS: Oliceridine (TRV130; [(3-methoxythiophen-2-yl)methyl]({2-[(9R)-9-(pyridin-2-yl)-6-oxaspiro[4.5]decan-9-yl]ethyl})amine) is a novel MOR agonist that selectively activates G protein and ß-arrestin signaling pathways. A growing body of evidence suggests that compared to existing MOR agonists, Oliceridine and other G protein-selective modulators may produce therapeutic analgesic effects with reduced adverse effects. Oliceridine provides analgesic benefits of a pure opioid agonist while limiting related adverse effects mediated through the ß-arrestin pathway. Recent insights into the function and structure of G protein-coupled receptors has led to the development of novel analgesic therapies.

Gastrointestinal adverse effects associated with the use of intravenous oliceridine compared with intravenous hydromorphone or fentanyl in acute pain management utilizing adjusted indirect treatment comparison methods.

Background: In the absence of head-to-head comparative data from randomized controlled trials, indirect treatment comparisons (ITCs) may be used to compare the relative effects of treatments versus a common comparator (either placebo or active treatment). For acute pain management, the effects of oliceridine have been compared in clinical trials to morphine but not to fentanyl or hydromorphone. Aim: To assess the comparative safety (specifically differences in the incidence of nausea, vomiting and opioid-induced respiratory depression [OIRD]) between oliceridine and relevant comparators (fentanyl and hydromorphone) through ITC analysis. Methods: A systematic literature review identified randomized clinical trials with oliceridine versus morphine and morphine versus fentanyl or hydromorphone. The ITC utilized the common active comparator, morphine, for the analysis. Results: A total of six randomized controlled trials (oliceridine - 2; hydromorphone - 3; fentanyl - 1) were identified for data to be used in the ITC analyses. The oliceridine data were reported in two studies (plastic surgery and orthopedic surgery) and were also reported in a pooled analysis. The ITC focused on nausea and vomiting due to limited data for OIRD. When oliceridine was compared with hydromorphone in the ITC analysis, oliceridine significantly reduced the incidence of nausea and/or vomiting requiring antiemetics compared with hydromorphone (both orthopedic surgery and pooled data), while results in plastic surgery were not statistically significant. When oliceridine was compared with hydromorphone utilizing data from Hong, the ITC only showed a trend toward reduced risk of nausea and vomiting with oliceridine that was not statistically significant across all three comparisons (orthopedic surgery, plastic surgery and combined). An ITC comparing oliceridine with a study of fentanyl utilizing the oliceridine orthopedic surgery data and combined orthopedic and plastic surgery data showed a trend toward reduced risk that was not statistically significant. Conclusion: In ITC analyses, oliceridine significantly reduced the incidence of nausea and/or vomiting or the need for antiemetics in orthopedic surgery compared with hydromorphone and a non-significant trend toward reduced risk versus fentanyl.

Pharmacokinetics and Safety of Oliceridine Fumarate Injection in Chinese Patients with Chronic Non-Cancer Pain: A Phase I, Single-Ascending-Dose, Open-Label Clinical Trial.

Background: Oliceridine is a novel G protein-biased ligand µ-opioid receptor agonist. This study aimed to assess the pharmacokinetics and safety profile of single-ascending doses of oliceridine fumarate injection in Chinese patients with chronic non-cancer pain. Methods: Conducted as a single-center, open-label trial, this study administered single doses of 0.75, 1.5, and 3.0 mg to 32 adult participants. The trial was conducted in two parts. First, we conducted a preliminary test comprising the administration of a single dose of 0.75mg to 2 participants. Then, we conducted the main trial involving intravenous administration of escalating doses of oliceridine fumarate (0.75 to 3 mg) to 30 participants. Pharmacokinetic (PK) parameters were derived using non-compartmental analysis. Additionally, the safety evaluation encompassed the monitoring of adverse events (AEs). Results: 32 participants were included in the PK and safety analyses. Following a 2-min intravenous infusion of oliceridine fumarate injection (0.75, 1.5, or 3 mg), Cmax and Tmax ranged from 51.293 to 81.914 ng/mL and 0.034 to 0.083 h, respectively. AUC0-t and half-life (t1/2) increased more than proportionally with dosage (1.85-2.084 h). Treatment emergent adverse events (TEAEs) were found to be consistent with the commonly reported adverse effects of opioids, both post-administration and as documented in the original trials conducted in the United States. Critically, no serious adverse events were observed. Conclusion: Oliceridine demonstrated comparable PK parameters and a consistent PK profile in the Chinese population, in line with the PK results observed in the original trials conducted in the United States. Oliceridine was safe and well tolerated in Chinese patients with chronic non-cancer pain at doses ranging from 0.75 mg to 3.0 mg. Trial Registration: The trial is registered at chictr.org.cn (ChiCTR2100047180).

Efficacy and safety of oliceridine treatment in patients with postoperative pain: a systematic review and meta-analysis of randomized controlled trials.

AIM: Our aim was to conduct a systematic review and meta-analysis to examine the efficacy and safety of oliceridine in patients with postoperative pain. METHODS: Four databases were searched from the beginning of the database to the present. We included all randomized controlled trials (RCT) that evaluated the efficacy and safety of oliceridine in patients with postoperative pain. Our endpoints were the proportion of treatment responders to the oliceridine regimen and the incidence of adverse effects such as nausea and vomiting. RESULTS: The analysis showed that more patients responded significantly with oliceridine compared to placebo. The proportion of treatment responders to oliceridine was comparable to that of morphine. Oliceridine had analgesia effects similar to morphine compared to placebo. The incidence of respiratory safety events was significantly lower with oliceridine compared to morphine. Oliceridine was significantly associated with more adverse events such as nausea and vomiting compared to placebo. The safety profile of oliceridine was superior to morphine compared to morphine. CONCLUSIONS: Our systematic review and meta-analysis showed that oliceridine is an effective and safe intravenous analgesic in patients with postoperative pain, producing rapid postoperative analgesic and usually well tolerated, and reducing incidence of adverse events compared to morphine. PROSPERO REGISTRATION: CRD42023391581.

Hyperactivity in Mice Induced by Opioid Agonists with Partial Intrinsic Efficacy and Biased Agonism Administered Alone and in Combination with Morphine.

Opioid analgesics such as morphine and fentanyl induce mu-opioid receptor (MOR)-mediated hyperactivity in mice. Herein, we show that morphine, fentanyl, SR-17018, and oliceridine have submaximal intrinsic efficacy in the mouse striatum using 35S-GTPγS binding assays. While all of the agonists act as partial agonists for stimulating G protein coupling in striatum, morphine, fentanyl, and oliceridine are fully efficacious in stimulating locomotor activity; meanwhile, the noncompetitive biased agonists SR-17018 and SR-15099 produce submaximal hyperactivity. Moreover, the combination of SR-17018 and morphine attenuates hyperactivity while antinociceptive efficacy is increased. The combination of oliceridine with morphine increases hyperactivity, which is maintained over time. These findings provide evidence that noncompetitive agonists at MOR can be used to suppress morphine-induced hyperactivity while enhancing antinociceptive efficacy; moreover, they demonstrate that intrinsic efficacy measured at the receptor level is not directly proportional to drug efficacy in the locomotor activity assay.

Novel Opioids in the Setting of Acute Postoperative Pain: A Narrative Review.

Although traditional opioids such as morphine and oxycodone are commonly used in the management of acute postoperative pain, novel opioids may play a role as alternatives that provide potent pain relief while minimizing adverse effects. In this review, we discuss the mechanisms of action, findings from preclinical studies and clinical trials, and potential advantages of several novel opioids. The more established include oliceridine (biased ligand activity to activate analgesia and downregulate opioid-related adverse events), tapentadol (mu-opioid agonist and norepinephrine reuptake inhibitor), and cebranopadol (mu-opioid agonist with nociceptin opioid peptide activity)-all of which have demonstrated success in the clinical setting when compared to traditional opioids. On the other hand, dinalbuphine sebacate (DNS; semi-synthetic mu partial antagonist and kappa agonist), dual enkephalinase inhibitors (STR-324, PL37, and PL265), and endomorphin-1 analog (CYT-1010) have shown good efficacy in preclinical studies with future plans for clinical trials. Rather than relying solely on mu-opioid receptor agonism to relieve pain and risk opioid-related adverse events (ORAEs), novel opioids make use of alternative mechanisms of action to treat pain while maintaining a safer side-effect profile, such as lower incidence of nausea, vomiting, sedation, and respiratory depression as well as reduced abuse potential.

Quantitative receptor model for responses that are left- or right-shifted versus occupancy (are more or less concentration sensitive): the SABRE approach.

Simple one-to three-parameter models routinely used to fit typical dose-response curves and calculate EC50 values using the Hill or Clark equation cannot provide the full picture connecting measured response to receptor occupancy, which can be quite complex due to the interplay between partial agonism and (pathway-dependent) signal amplification. The recently introduced SABRE quantitative receptor model is the first one that explicitly includes a parameter for signal amplification (γ) in addition to those for binding affinity (K d), receptor-activation efficacy (ε), constitutive activity (ε R0), and steepness of response (Hill slope, n). It can provide a unified framework to fit complex cases, where fractional response and occupancy do not match, as well as simple ones, where parameters constrained to specific values can be used (e.g., ε R0 = 0, γ = 1, or n = 1). Here, it is shown for the first time that SABRE can fit not only typical cases where response curves are left-shifted compared to occupancy (κ = K d/EC50 > 1) due to signal amplification (γ > 1), but also less common ones where they are right-shifted (i.e., less concentration-sensitive; κ = K d/EC50 < 1) by modeling them as apparent signal attenuation/loss (γ < 1). Illustrations are provided with µ-opioid receptor (MOPr) data from three different experiments with one left- and one right-shifted response (G protein activation and ß-arrestin2 recruitment, respectively; EC50,Gprt < K d < EC50,ßArr). For such cases of diverging pathways with differently shifted responses, partial agonists can cause very weak responses in the less concentration-sensitive pathway without having to be biased ligands due to the combination of low ligand efficacy and signal attenuation/loss-an illustration with SABRE-fitted oliceridine data is included.

Oliceridine- Opioid of the 21st Century.

Oliceridine (Olinvyk® Trevena, PA, USA) was approved by the United States Food and Drug Administration for clinical use on Aug 8, 2020. Even though, the indication of its approval is very restrictive (to manage moderate-to-severe acute pain in adults when the pain is severe enough), for such an innovative opioid, off-label indications are bound to abound. What could be described as the "opioid of the century," it aims to overcome some of the stubbornest barriers to opioid prescribing, namely addiction liability, respiratory depression, and gastrointestinal (GI) side effects, just to name a few. The novel opioid accomplishes this by a unique mechanism of action. By selectively acting on the G-protein sub-pathway in preference to the beta-arrestin, it aims to mitigate these unwanted µ-opioid receptors-associated opioid side effects, while preserving its analgesic activity. What remains to be seen, however, is if these observations seen in phases 2 and 3 trials will be borne in actual large-scale clinical use, both inside and outside the USA. Unfortunately, the field of anesthesia is rife with innovations that have shown enormous promise at the research stage, only to end up as damp squibs when released to the clinicians for general use. Rapcuronium and althesin are some such examples. We aim to present some of the contentious and emerging issues associated with this drug and some of the potential pitfalls of this new opioid.

Evaluating oliceridine as a treatment option for moderate to severe acute post-operative pain in adults.

INTRODUCTION: Despite the advances in regional anesthesia and non-opioid systemic analgesia, opioids remain the primary rescue analgesic for moderate to severe pain. However, the risks and side effects of opioid medications are well documented. Oliceridine is a novel opioid receptor agonist which is thought to have less risk of adverse events, such as postoperative nausea and vomiting (PONV) and respiratory depression. AREAS COVERED: In this review, the authors discuss the limitations of the current opioid and non-opioid analgesic options. They also review the pharmacokinetics of oliceridine, its analgesic efficacy, and risk of adverse events; and its added clinical value in managing moderate to severe pain. EXPERT OPINION: Despite the advances in regional anesthesia and multimodal systemic analgesia, opioid free analgesia is only feasible in selected procedures and patients. Oliceridine is effective in the management of moderate to severe pain and appears to be associated with lower risk of nausea and vomiting. The risk of sedation and respiratory depression associated with oliceridine will require further study. The availability of an opioid agonist with a better side effect profile could potentially change the current paradigm of opioid avoidance in postoperative pain management.

Budget impact and pharmacy costs with targeted use of oliceridine for postsurgical pain in patients at high risk of opioid-related adverse events.

BACKGROUND: Oliceridine, a new class of µ-opioid receptor agonist, may be associated with fewer opioid-related adverse events (ORAEs) due to its unique mechanism of action. Thus, it may provide a cost-effective alternative to conventional opioids such as morphine. PATIENTS AND METHODS: Using a decision tree with a 24-hour time horizon, we calculated costs for medication and management of the three most common AEs (oxygen saturation <90%, vomiting, somnolence) following postoperative oliceridine or morphine in high-risk patients. Costs were enumerated as differences in cost of analgesics and resource utilization in the first 24 hours post-surgery. An economic model compared expected AEs and costs in a blended cohort where elderly/obese patients at higher risk for ORAEs received oliceridine while those presumed to be at lower risk received morphine with a cohort that received morphine alone. RESULTS: In high-risk patients, use of oliceridine resulted in overall savings of $363,944 (in 1,000 patients). Implementing a targeted approach of oliceridine utilization in patients with high risk for ORAEs can save a typical hospital system $122,296 in total cost of care. CONCLUSION: Use of oliceridine in postoperative care among patients at high risk provides a favorable health economic benefit compared to the use of morphine.

Oliceridine, a new class of opioid analgesics, administered directly into a vein, is a unique medication in that it provides pain relief equivalent to morphine and may have less costly side effects. It is given in a hospital/clinic or surgery center for the treatment of postoperative pain and can reduce costs compared to other opioid analgesics, possibly due to less side effects. An economic model was developed that compares morphine to oliceridine in patients more likely to experience sides effects due to traditional pain medications, comparing common side effects and pain relief following surgery. Although oliceridine costs more than morphine, in our economic model, the use of oliceridine resulted in cost savings ($363,944 US 2020 Dollars in 1,000 patients), and a positive return of investment of over 7 times, when compared to morphine.

Preclinical discovery and development of oliceridine (Olinvyk®) for the treatment of post-operative pain.

INTRODUCTION: Opioids acting at the MOP (mu:µ) receptor produce analgesia but also side effects. There is debate suggesting opioid receptors produce analgesia via G-protein and side-effects via ß-arrestin-2 pathways. Opioids targeting G-proteins over the arrestins (bias) offer potential therapeutic advantages. Oliceridine is a putative MOP, G-protein biased agonist. AREAS COVERED: Oliceridine is selective for MOP receptors with greater activity at G-proteins over arrestins. A substantial body of evidence now points to a simpler pharmacological descriptor of partial agonist. Preclinical in vivo data indicates a robust antinociceptive response of shorter duration than morphine. Apollo trials (Phase-III RCT-bunionectomy/abdominoplasty) describe good analgesic efficacy that was non-inferior to morphine with good tolerability and side-effect profile. There is evidence for an improved respiratory safety profile. Oliceridine is approved by the FDA. EXPERT OPINION: Oliceridine will be an important addition to the clinical armamentarium for use for the management of acute pain severe enough to require an intravenous opioid analgesic and for whom alternative treatments are inadequate. Respiratory advantage and the possibility of reduced abuse potential are possible advantages over the use of traditional opioids. Based on a number of excellent, highly detailed studies, oliceridine should be described as a partial agonist; this 'label' does not matter.

A critical review of oliceridine injection as an IV opioid analgesic for the management of severe acute pain.

INTRODUCTION: Oliceridine is a G protein-selective (biased) agonist at the µ-opioid receptor, with less recruitment of ß-arrestin-2, a signaling pathway associated with opioid-related adverse events. Nonclinical evidence showed that oliceridine elicits a rapid systemic analgesic effect while attenuating opioid-related adverse events. AREAS COVERED: Three pivotal studies in patients with moderate-to-severe acute pain, including two randomized, double-blind, placebo- and morphine-controlled efficacy studies following either orthopedic surgery-bunionectomy or plastic surgery-abdominoplasty; and an open-label safety study following a surgical procedure or due to a medical condition. EXPERT OPINION: Poorly controlled acute postoperative pain is associated with poorer recovery, longer hospitalization, increased complications, and worse healthcare outcomes. Recently, oliceridine intravenous injection was approved for use in adults for the management of acute pain severe enough to require an intravenous opioid analgesic and for whom alternative treatments are inadequate. Introduction of this new IV opioid provides a valuable option to manage postoperative pain.

Opioid MOP receptor agonists in late-stage development for the treatment of postoperative pain.

INTRODUCTION: Opioids remain important in postoperative analgesia although, the focus is on using them as part of multimodal regimens where it is not possible to avoid their use completely. The development of novel agents with more favorable adverse effect profiles may increase safety whilst maintaining efficacy. AREAS COVERED: This article reviews the clinical trials for opioids in late-stage development. The objective of this narrative review is to evaluate the pharmacokinetic properties, safety, tolerability, and analgesic efficacy of these agents in the management of postoperative pain. EXPERT OPINION: Oliceridine appears to be an effective and potentially safer µ opioid receptor agonist. Its main advantages are a relatively fast onset with reduced respiratory depression, nausea, and vomiting. Cebranopadol is an agonist at multiple opioid receptors, of which µ opioid and nociceptin/orphanin FQ peptide (NOP) receptor are most significant. It is an oral drug that appears to have efficacy in neuropathic pain, with reduced respiratory depression and abuse potential. Lastly, morphine-6-glucuronide is an active metabolite of morphine with a slower onset than its parent compound. It has failed to demonstrate appreciable benefit in the context of postoperative analgesia.