Prophylaxis and treatment of the side-effects of neuraxial morphine analgesia following cesarean delivery

Differential Effects of a Novel Opioid Ligand UTA1003 on Antinociceptive Tolerance and Motor Behaviour

Analgesic tolerance is a major problem in the clinic for the maintenance of opioid-induced long-term pain relief. Opioids with mixed activity on multiple opioid receptors promise reduced antinociceptive tolerance in preclinical studies, but these compounds typically show poor bioavailability upon oral, subcutaneous, intraperitoneal, or intravenous administration. We designed UTA1003 as a novel opioid that acts as a mu (MOP) and kappa (KOP) opioid receptor agonist and a partial agonist for delta (DOP) opioid receptor. In the present study, its antinociceptive effects, as well as its effects on antinociceptive tolerance and motor behaviour, were investigated in male rats. Acute antinociception was measured before (basal) and at different time points after subcutaneous injection of UTA1003 or morphine using the tail flick and hot plate assays. Various motor behavioural activities, including horizontal locomotion, rearing, and turning, were automatically measured in an open-field arena. The antinociceptive and behavioural effects of repeated administration of UTA1003 and morphine were determined over eight days. UTA1003 induced mild antinociceptive effects after acute administration but induced no tolerance after repeated treatment. Importantly, UTA1003 co-treatment with morphine prevented antinociceptive tolerance compared to morphine alone. UTA1003 showed less motor suppression than morphine in both acute and sub-chronic treatment regimens, while it did not affect morphine-induced motor suppression or hyper-excitation. Based on these activities, we speculate that UTA1003 crosses the blood-brain barrier after subcutaneous administration and, therefore, could be developed as a lead molecule to avoid opioid-induced antinociceptive tolerance and motor suppression. Further structural modifications to improve its antinociceptive effects, toxicity profile, and ADME parameters are nevertheless required.

Impact of Transversus Abdominis Plane Block With Bupivacaine or Ropivacaine Versus Intrathecal Morphine on Opioid-related Side Effects After Cesarean Delivery: A Meta-analysis of Randomized Controlled Trials

OBJECTIVES

Intrathecal morphine (ITM) is frequently associated with side effects such as postoperative nausea and vomiting (PONV) and pruritus. The aim of this meta-analysis was to compare the impact of transversus abdominis plane (TAP) block versus ITM on side effects following cesarean delivery.

MATERIALS AND METHODS

PubMed, Embase, Web of Science, and CENTRAL were searched for randomized controlled trials that compared TAP with ITM for cesarean delivery. The primary outcomes were opioid-related side effects. The secondary outcomes included pain scores, opioid consumption, patient satisfaction, and time to the first analgesia request.

RESULTS

Seven studies involving 660 patients were included. TAP blocks were performed with bupivacaine or ropivacaine. There was less PONV with TAP versus ITM (risk ratio [RR]=0.45, 95% confidence interval [CI]: 0.33-0.63, P<0.001; I2=0%), but no significant difference in pruritus (RR=0.76, 95% CI: 0.49-1.18, P=0.22; I2=78%) and sedation (RR=0.44, 95% CI: 0.19-1.00, P=0.05; I2=0%). TAP had a greater morphine consumption in 24 hours (mean difference: 5.80 mg; 95% CI: 1.38-10.22 mg, P=0.01; I2=89%) and higher pain score at rest at 6 hours (mean difference: 0.70, 95% CI: 0.39-1.02, P<0.001; I2=56%), but similar pain at rest at 24 hours and on movement compared with ITM. No differences were found in time to first analgesia and patient satisfaction.

DISCUSSION

Compared with ITM, TAP block is associated with less PONV but inferior early analgesia after cesarean delivery. However, the heterogeneity among the studies highlights the need for more well-designed studies to obtain more robust conclusions.

Opioid Analgesia and Opioid-Induced Adverse Effects: A Review

Opioids are widely used as therapeutic agents against moderate to severe acute and chronic pain. Still, these classes of analgesic drugs have many potential limitations as they induce analgesic tolerance, addiction and numerous behavioural adverse effects that often result in patient non-compliance. As opium and opioids have been traditionally used as painkillers, the exact mechanisms of their adverse reactions over repeated use are multifactorial and not fully understood. Older adults suffer from cancer and non-cancer chronic pain more than younger adults, due to the physiological changes related to ageing and their reduced metabolic capabilities and thus show an increased number of adverse reactions to opioid drugs. All clinically used opioids are μ-opioid receptor agonists, and the major adverse effects are directly or potentially connected to this receptor. Multifunctional opioid ligands or peripherally restricted opioids may elicit fewer adverse effects, as shown in preclinical studies, but these results need reproducibility from further extensive clinical trials. The current review aims to overview various mechanisms involved in the adverse effects induced by opioids, to provide a better understanding of the underlying pathophysiology and, ultimately, to help develop an effective therapeutic strategy to better manage pain.

Profiling the Effects of Repetitive Morphine Administration on Motor Behavior in Rats

Efficient repetitive clinical use of morphine is limited by its numerous side effects, whereas analgesic tolerance necessitates subsequent increases in morphine dose to achieve adequate levels of analgesia. While many studies focused on analgesic tolerance, the effect of morphine dosing on non-analgesic effects has been overlooked. This study aimed to characterize morphine-induced behavior and the development and progression of morphine-induced behavioral tolerance. Adult male Sprague-Dawley rats were repetitively treated with subcutaneous morphine for 14 days in two dose groups (A: 5 mg/kg/day (b.i.d.) → 10 mg/kg/day; B: 10 mg/kg/day (b.i.d.) → 20 mg/kg/day). Motor behavior was assessed daily (distance traveled, speed, moving time, rearing, rotation) in an open-field arena, before and 30 min post-injections. Antinociception was measured using tail-flick and hot-plate assays. All measured parameters were highly suppressed in both dosing groups on the first treatment day, followed by a gradual manifestation of behavioral tolerance as the treatment progressed. Animals in the high-dose group showed increased locomotor activity after 10 days of morphine treatment. This excitatory phase converted to an inhibition of behavior when a higher morphine dose was introduced. We suggest that the excitatory locomotor effects of repetitive high-dose morphine exposure represent a signature of its behavioral and antinociceptive tolerance.

Ondansetron versus ondansetron with dexamethasone to prevent intrathecal-morphine pruritus for caesarean patients: randomised double-blind trial

The objective of this randomised, double blinded clinical trial was to evaluate the efficacy of prophylactic administration of 4 mg ondansetron as monotherapy versus combination therapy of 4 mg ondansetron plus 8 mg dexamethasone for the prevention of intrathecal morphine-associated pruritus in caesarean section within 24 h. A total of 194 patients were included, 96 patients in the monotherapy group and 98 in the combination group. One hour after the operation, 11.5% of patients in ondansetron group had failure of prophylaxis for pruritus compared to 13.5% of patients in the combination group (p = .66). This decreased throughout the follow-up to reach 0.0% and 1.0% at 24 h in the ondansetron vs. the combination groups respectively. There was no superiority of combining ondansetron with dexamethasone over the use of ondansetron as prophylactic antipruritic in parturients receiving intrathecal morphine for caesarean section.IMPACT STATEMENTWhat is already known on this subject? The incidence of pruritus has been reported to be between 36% and 60% in patients undergoing caesarean section with intrathecal morphine. Ondansetron has been identified as possible antipruritic agent while the antipruritic effect of dexamethasone is inconclusive.What do the results of this study add? The study demonstrated that there was no superiority of combining ondansetron with dexamethasone over the use of ondansetron as prophylactic antipruritic in parturients receiving intrathecal morphine for caesarean section. Moreover, it seems that there is no effect of combining ondansetron with dexamethasone over ondansetron alone on antiemetic consequences.What are the implications of these findings for clinical practice and/or further research? Ondansetron could be an effective antipruritic if used solely for patients undergoing caesarean section.

Translational value of non-human primates in opioid research

Preclinical opioid research using animal models not only provides mechanistic insights into the modulation of opioid analgesia and its associated side effects, but also validates drug candidates for improved treatment options for opioid use disorder. Non-human primates (NHPs) have served as a surrogate species for humans in opioid research for more than five decades. The translational value of NHP models is supported by the documented species differences between rodents and primates regarding their behavioral and physiological responses to opioid-related ligands and that NHP studies have provided more concordant results with human studies. This review highlights the utilization of NHP models in five aspects of opioid research, i.e., analgesia, abuse liability, respiratory depression, physical dependence, and pruritus. Recent NHP studies have found that (1) mixed mu opioid and nociceptin/orphanin FQ peptide receptor partial agonists appear to be safe, non-addictive analgesics and (2) mu opioid receptor- and mixed opioid receptor subtype-based medications remain the only two classes of drugs that are effective in alleviating opioid-induced adverse effects. Given the recent advances in pharmaceutical sciences and discoveries of novel targets, NHP studies are posed to identify the translational gap and validate therapeutic targets for the treatment of opioid use disorder. Pharmacological studies using NHPs along with multiple outcome measures (e.g., behavior, physiologic function, and neuroimaging) will continue to facilitate the research and development of improved medications to curb the opioid epidemic.

The Role of Bacteria and Its Derived Metabolites in Chronic Pain and Depression: Recent Findings and Research Progress

BACKGROUND

Chronic pain is frequently comorbid with depression in clinical practice. Recently, alterations in gut microbiota and metabolites derived therefrom have been found to potentially contribute to abnormal behaviors and cognitive dysfunction via the "microbiota-gut-brain" axis.

METHODS

PubMed was searched and we selected relevant studies before October 1, 2019. The search keyword string included "pain OR chronic pain" AND "gut microbiota OR metabolites"; "depression OR depressive disorder" AND "gut microbiota OR metabolites". We also searched the reference lists of key articles manually.

RESULTS

This review systematically summarized the recent evidence of gut microbiota and metabolites in chronic pain and depression in animal and human studies. The results showed the pathogenesis and therapeutics of chronic pain and depression might be partially due to gut microbiota dysbiosis. Importantly, bacteria-derived metabolites, including short-chain fatty acids, tryptophan-derived metabolites, and secondary bile acids, offer new insights into the potential linkage between key triggers in gut microbiota and potential mechanisms of depression.

CONCLUSION

Studying gut microbiota and its metabolites has contributed to the understanding of comorbidity of chronic pain and depression. Consequently, modulating dietary structures or supplementation of specific bacteria may be an available strategy for treating chronic pain and depression.

Incidence and risk factors for epidural morphine induced pruritus in parturients receiving cesarean section: A prospective multicenter observational study

This study is designed to clarify the incidence of epidural morphine induced pruritus (EMIP) in Chinese Han and Tibetan parturients after cesarean section (CS) and to identify the correlated risk factors.This is a prospective multicenter observational study. Follow-up evaluations were performed at 3 hours, 6 hours, 12 hours, 24 hours, and 48 hours after morphine administration. The primary outcome was EMIP incidence. Other details were also recorded for risk factor screening.Totally 284 parturients receiving CS were enrolled and 247 completed the study. The overall incidence of EMIP was 18.6% (46 in 247). The onset of pruritus was 5.6 ± 4.8 hours (mean ± SD) after morphine administration and the duration of pruritus was 14.0 ± 8.8 hours. Logistic regression models was built with 5 variables, history of allergy, serotonin receptor antagonist administration, I.V. fentanyl administration, epidural morphine volume and VAS pain score. Results of showed that 2 of the variables, history of allergy (P < .001) and serotonin receptor antagonist (P < .05), were significantly correlated with incidence of EMIP.In conclusion, EMIP incidence in our study was 18.6%. Positive medical history of allergy and not using serotonin receptor antagonist were potential risk factors of EMIP development.Trial registration: ChiCTR-OPC-17012345.

Palonosetron versus ondansetron for prevention of nausea and vomiting after total abdominal hysterectomy under spinal anesthesia with intrathecal morphine: a double-blind, randomized controlled trial

Background

Hysterectomy is a widely performed surgery and neuraxial anesthesia with intrathecal morphine provides superior quality of recovery. Postoperative nausea and vomiting (PONV) is a frequent problem with intrathecal morphine use. Although palonosetron is effective for prevention of PONV after general anesthesia, its efficacy after neuraxial anesthesia has not been established. This study was conducted to compare the use of palonosetron with ondansetron for PONV prophylaxis in patients at a high risk of PONV during total abdominal hysterectomy (TAH) under spinal anesthesia with intrathecal morphine.

Methods

This prospective, randomized double-blind study conducted at São Rafael Hospital involved 140 American Society of Anesthesiologists physical status I or II women who underwent TAH under spinal anesthesia with intrathecal morphine and who had at least 3 risk factors for PONV based on Apfel’s simplified score. The patients were randomized into two groups: one received palonosetron whereas the other received ondansetron. All patients received spinal anesthesia with intrathecal morphine, as well as dexamethasone plus palonosetron or ondansetron for PONV prophylaxis. The overall incidence of PONV, incidence of early- and late-onset nausea and vomiting, severity of nausea, and use of rescue antiemetics were recorded.

Results

The overall incidence of PONV was 42.9% in the palonosetron group and 52.9% in the ondansetron group (p > 0.05). No significant differences existed in the incidence of early- and late-onset nausea or early-onset vomiting between the two groups. The incidence of late-onset vomiting was significantly lower in the palonosetron group.

Conclusions

Palonosetron exhibited efficacy similar to that of ondansetron for reducing the overall incidence of PONV after TAH under spinal anesthesia with intrathecal morphine; however, palonosetron reduced the incidence of late-onset vomiting significantly better than ondansetron.

Trial registration

RBR-4gnm8n (ensaiosclinicos.gov.br), date of registration: August 18, 2014.

Prophylactic granisetron for post-spinal anesthesia shivering in cesarean section: A randomized controlled clinical study

BACKGROUND

The serotonergic system is known to be involved in control of post-anesthetic shivering. Our hypothesis was that prophylactic granisetrone (serotonin antagonist) might reduce incidence of post-spinal anesthesia shivering in cesarean section.

METHODS

Parturient scheduled for elective cesarean delivery under spinal anesthesia were allocated to receive 0.9% saline (Group I, n = 71), 1 mg granisetron (Group II, n = 69), or 0.7 mg granisetron (Group III, n = 72) before the spinal block. Assessment parameters included; hemodynamics, tympanic membrane temperature, neonatal Apgar score, shivering score, patient satisfaction scores about shivering prophylaxis and adverse effects.

RESULTS

Clinically significant shivering was recorded in 55/71 patients (77.5%) in group I, 11/69 (15.9%) in group II and 21/72 (29.2%) in group III (P = 0.000). The intensity of shivering was significantly lower in patients who received granisetron 1 mg compared with granisetron 0.7 mg or saline (P = 0.000). Patients who received prophylactic granisetron 1 mg reported lower mean intraoperative arterial pressure and heart rate values and consumed higher doses of iv ephedrine compared with 0.7 mg granisetron or saline placebo (P < 0.05). Pruritus significantly decreased from (22.5%) in control group to (0%) in granisetron groups (P = 0.000). Nausea was reported in 8 vs 10 and four in group I, II and III, respectively (P < 0.03). Sixteen vs eight and six patients vomited in group I, II, and III, respectively (P < 0.03). Higher patient satisfaction scores were recorded in group II (9.83 ± 0.29, P < 0.03) and III (9.14 ± 1.04, P < 0.04), compared with control group (8.23 ± 1.14).

CONCLUSION

Prophylactic granisetron effectively reduced incidence and severity of perioperative shivering in a dose dependent manner, compared to placebo controls.

Neuraxial morphine after unintentional dural puncture is not associated with reduced postdural puncture headache in obstetric patients

STUDY OBJECTIVE

To examine the relationship between neuraxial morphine exposure after unintentional dural puncture and the risk for postdural puncture headache in obstetric patients.

DESIGN

Retrospective cohort study.

SETTING

Obstetrical unit at a tertiary care referral center.

PATIENTS

Parturients receiving labor epidural analgesia with recognized unintentional dural puncture.

INTERVENTIONS

Cases in which neuraxial morphine was given for any reason were compared to cases in which it was not for the outcome of postdural puncture headache.

MEASUREMENTS

Development of postdural puncture headache, headache severity, number of epidural blood patches, hospital length of stay.

MAIN RESULTS

Of the 80 cases that were included, 38 women received neuraxial morphine and 42 did not. There was no significant difference in the incidence of headache between the two morphine groups (Headache present: Morphine: 27/56 [48.2%], No morphine: 29/56 [51.8%]; Headache free: Morphine: 11/24 [45.8%], No morphine: 13/24 [54.2%], P = 0.84). There was no difference in the need for epidural blood patch (Morphine: 24/42 [57.1%], No morphine: 18/38 [47.4%], P = 0.50) and headache severity (mean headache pain score: Morphine: 7.9 ± 1.8 vs. No morphine: 7.3 ± 2.4, P = 0.58). Hospital length of stay was higher in the morphine group (4.4 ± 2.9 days vs. 3.0 ± 1.5 days respectively, P = 0.008). Using logistic regression, morphine did not affect headache risk after controlling for covariates (morphine vs. no morphine: adjusted OR 1.24 [0.75]; P = 0.72; pre-eclampsia vs. no pre-eclampsia: adjusted OR 0.56 [0.41], P = 0.42; cesarean vs. normal spontaneous vaginal delivery: adjusted OR 0.97 [0.67]; P = 0.96).

CONCLUSION

In cases of unintentional dural puncture, exposure to neuraxial morphine for any reason may not be protective against the risk of postdural puncture headache. Although an overall protective effect of neuraxial morphine was not observed in this study, its role in specific subsets of patients remains to be investigated.

NMDA receptor antagonists attenuate intrathecal morphine-induced pruritus through ERK phosphorylation

Pruritus is the most common complication of intrathecal morphine; however, its exact molecular mechanism is unclear, and treatment is challenging. The analgesic effect of N-methyl-D-aspartate (NMDA) receptor antagonists and the morphine-associated increase in NMDA receptor activation suggest potential role of NMDA receptor in the spinal itch sensation. Male C57BL/6 mice were given intrathecal morphine to induce scratching behavior. The effects of NMDA, ketamine, ifenprodil and U0126 on morphine-induced pruritus and analgesia were evaluated also. The number of scratching responses was counted for 30 min post-injection to evaluate pruritus. A warm-water tail immersion assay was conducted before and until 120 min post-injection at 30-min intervals. Percent of maximal possible effect (%MPE) and area under curve (AUC) were calculated based on tail-flick latency to evaluate analgesic efficacy. Compared with control treatment, intrathecal morphine elicited an obvious scratching response and analgesic effect in a dose dependent manner. Ketamine (1 μg), ifenprodil (0.1 μg) and U0126 (0.1 μg and 1.0 μg) all significantly attenuated morphine induced scratches. Ifenprodil (0.1 μg) injection significantly prolonged the analgesic effect of intrathecal morphine. The ERK1/2 phosphorylation induced by intrathecal morphine was inhibited by ketamine, ifenprodil and U0126 as well. U0126 inhibited morphine-induced pruritus with no effect on its analgesia. Therefore, intrathecal coadministration of morphine with NMDA receptor antagonists ketamine and ifenprodil alleviated morphine-induced scratching. Intrathecal morphine increased ERK phosphorylation in the lumbar spinal dorsal horn, which may be related with morphine-induced pruritus, and was counteracted by NMDA receptor antagonists.

Ondansetron for neuraxial morphine-induced pruritus: A meta-analysis of randomized controlled trials

WHAT IS KNOWN AND OBJECTIVE

Pruritus is one of the most common adverse effects associated with neuraxial morphine. Ondansetron has been used to deal with the problem of neuraxial morphine-induced pruritus (NMIP). The aim of this meta-analysis was to evaluate the preventive efficacy of ondansetron on NMIP.

METHODS

Online databases such as PubMed, EMBASE and the Cochrane Central Register of Controlled Trials were searched for eligible randomized controlled trials (RCTs). The primary outcome was the incidence of NMIP. We calculated risk ratios (RR) with 95% confidence intervals (CI) for dichotomous data. Trial sequential analysis (TSA) was performed to avoid the risk of making a spurious claim of significant effect and to calculate the sample size necessary to make a robust claim of effect.

RESULTS AND DISCUSSION

Our traditional meta-analysis showed that prophylactic ondansetron could significantly reduce the incidence of NMIP in non-obstetric patients (three trials, RR=0.63, 95% CI 0.45-0.89, P=.008) with modest heterogeneity (I² =47%) while it did not show the preventive efficacy of NMIP in obstetric patients (seven trials, RR=0.84, 95% CI 0.69-1.03, P=.10) with obvious heterogeneity (I²  =82% ). However, TSA demonstrates that more high-quality RCTs are still needed to confirm the preventive efficacy of ondansetron on NMIP in non-obstetric populations and to study whether ondansetron prevents NMIP in obstetric patients.

WHAT IS NEW AND CONCLUSION

Prophylactic ondansetron can significantly reduce the incidence of NMIP in non-obstetric patients but not in obstetric patients. However, more well-designed trials are still required to test the reliability of the results in our traditional meta-analysis.

Magnesium Sulfate Mediates Morphine Administration Reduction in Varicocelectomy Surgery

AIMS

Varicocelectomy is the most common operation carried out by doctors for male infertility treatment. The aim of varicocele treatment is to hinder the refluxing venous drainage to the testis, retaining arterial inflow, and lymphatic drainage. A lot of pain is generated after this surgery, and the use of opium should be reduced to nearest minimum, as all drugs are toxins. Thus the aim of the present study is to facilitate morphine usage reduction after varicocelectomy surgery.

MATERIAL AND METHODS

One-hundred (100) patients who were varicocelectomy candidate were randomized into two groups: experimental group contain 50 patients and control group contain 50 patients as well. In experimental group, 2 mL magnesium sulfate in 2 mL normal saline was injected into patient immediately after surgery. The control group received only 4 mL normal saline. Morphine dosage administered, and severity of pain monitoring was accessed and recorded with a visual analogue scale (VAS).

RESULT

Result indicated that administration of morphine dosage in the test group 0.21 ± 0.64 mg was significantly lower as compared to the control group 0.75 ± 1.30 mg during the first 24-hour after surgery (p = 0.01). Average VAS scores in the experimental and control groups in the first 4-hour interval were 0.91 ± 1.30 and 2.9 ± 2.50 (p = 0.02) respectively. We observed a significant difference in the VAS score for pain severity and the dosages of morphine administered.

CONCLUSIONS

The experimental group with magnesium sulfate in its drug formulation showed better pain control compared to the control group which received only normal saline, whose pain manifested after every few hours. This can be used for the formulation of opium for this surgery in a large scale.

A review of opioid-induced itching after cesarean birth

Currently, about one-third of all women giving birth have a cesarean surgical birth, and the majority are given an epidural or spinal anesthetic containing an opioid for surgery. An unpleasant side effect experienced by many of these women is itching. This article reviews the literature on itching after spinal and epidural administration of opioids and how nurses can best manage this side effect.

Neuraxial opioid-induced itch and its pharmacological antagonism

Given its profound analgesic nature, neuraxial opioids are frequently used for pain management. Unfortunately, the high incident rate of itch/pruritus after spinal administration of opioid analgesics reported in postoperative and obstetric patients greatly diminishes patient satisfaction and thus the value of the analgesics. Many endeavors to solve the mystery behind neuraxial opioid-induced itch had not been successful, as the pharmacological antagonism other than the blockade of mu opioid receptors remains elusive. Nevertheless, as the characteristics of all opioid receptor subtypes have become more understood, more studies have shed light on the potential effective treatments. This review discusses the mechanisms underlying neuraxial opioid-induced itch and compares pharmacological evidence in nonhuman primates with clinical findings across diverse drugs. Both nonhuman primate and human studies corroborate that mixed mu/kappa opioid partial agonists seem to be the most effective drugs in ameliorating neuraxial opioid-induced itch while retaining neuraxial opioid-induced analgesia.

Supraspinal actions of nociceptin/orphanin FQ, morphine and substance P in regulating pain and itch in non-human primates

BACKGROUND AND PURPOSE

Nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor agonists display a promising analgesic profile in preclinical studies. However, supraspinal N/OFQ produced hyperalgesia in rodents and such effects have not been addressed in primates. Thus, the aim of this study was to investigate the effects of centrally administered ligands on regulating pain and itch in non-human primates. In particular, nociceptive thresholds affected by intracisternal N/OFQ were compared with those of morphine and substance P, known to provide analgesia and mediate hyperalgesia, respectively, in humans.

EXPERIMENTAL APPROACH

Intrathecal catheters were installed to allow intracisternal and lumbar intrathecal administration in awake and unanaesthetized rhesus monkeys. Nociceptive responses were measured using the warm water tail-withdrawal assay. Itch scratching responses were scored from videotapes recording behavioural activities of monkeys in their home cages. Antagonist studies were conducted to validate the receptor mechanisms underlying intracisternally elicited behavioural responses.

KEY RESULTS

Intracisternal morphine (100 nmol) elicited more head scratches than those after intrathecal morphine. Distinct dermatomal scratching locations between the two routes suggest a corresponding activation of supraspinal and spinal μ receptors. Unlike intracisternal substance P, which induced hyperalgesia, intracisternal N/OFQ (100 nmol) produced antinociceptive effects mediated by NOP receptors. Neither peptide increased scratching responses.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results demonstrated differential actions of ligands in the primate supraspinal region in regulating pain and itch. This study not only improves scientific understanding of the N/OFQ-NOP receptor system in pain processing but also supports the therapeutic potential of NOP-related ligands as analgesics.

Brief review: Neuraxial analgesia in refractory malignant pain

PURPOSE

This narrative review aims to inform health care practitioners of the current literature surrounding the use of intrathecal (IT) and epidural analgesia in cancer patients with refractory pain at end of life. Topics discussed and reviewed include: patient selection, treatment planning, procedure, equipment, medications, complications, policies and procedures, as well as directions for future research.

PRINCIPAL FINDINGS

Cancer pain is inadequately treated in an estimated 10% of patients with malignant pain despite the implementation of the World Health Organization three-step analgesic ladder. This has prompted some to advocate for the addition of a fourth step that would include neuraxial interventions. There is moderate evidence supporting the safety and efficacy of IT drug therapy in cancer patients with refractory pain. A detailed assessment and interdisciplinary team approach is necessary to develop and implement care plans for patients requiring neuraxial analgesia. Neuraxial analgesia can significantly improve pain and reduce side effects, but this must be balanced against the increased complexity of care and the risk of uncommon but serious complications.

CONCLUSION

Neuraxial drug delivery gives clinicians more options to manage refractory pain at end of life and should be offered to patients with intractable cancer pain. Teams should be interprofessional with clear delineation of roles and responsibilities. They should discuss advanced discharge planning with the patient prior to implantation as well as provide on-call support.

Mu opioid receptors on primary afferent nav1.8 neurons contribute to opiate-induced analgesia: insight from conditional knockout mice

Opiates are powerful drugs to treat severe pain, and act via mu opioid receptors distributed throughout the nervous system. Their clinical use is hampered by centrally-mediated adverse effects, including nausea or respiratory depression. Here we used a genetic approach to investigate the potential of peripheral mu opioid receptors as targets for pain treatment. We generated conditional knockout (cKO) mice in which mu opioid receptors are deleted specifically in primary afferent Nav1.8-positive neurons. Mutant animals were compared to controls for acute nociception, inflammatory pain, opiate-induced analgesia and constipation. There was a 76% decrease of mu receptor-positive neurons and a 60% reduction of mu-receptor mRNA in dorsal root ganglia of cKO mice. Mutant mice showed normal responses to heat, mechanical, visceral and chemical stimuli, as well as unchanged morphine antinociception and tolerance to antinociception in models of acute pain. Inflammatory pain developed similarly in cKO and controls mice after Complete Freund's Adjuvant. In the inflammation model, however, opiate-induced (morphine, fentanyl and loperamide) analgesia was reduced in mutant mice as compared to controls, and abolished at low doses. Morphine-induced constipation remained intact in cKO mice. We therefore genetically demonstrate for the first time that mu opioid receptors partly mediate opiate analgesia at the level of Nav1.8-positive sensory neurons. In our study, this mechanism operates under conditions of inflammatory pain, but not nociception. Previous pharmacology suggests that peripheral opiates may be clinically useful, and our data further demonstrate that Nav1.8 neuron-associated mu opioid receptors are feasible targets to alleviate some forms of persistent pain.