Methadone for postoperative analgesia: contribution of N-methyl-D-aspartate receptor antagonism: A randomised controlled trial

Continuous Wound Irrigation and Intraoperative Methadone Decreases Opioid Use and Shortens Length of Stay After CRS/HIPEC

BACKGROUND

Epidural analgesia is resource and labor intense and may limit postoperative management options and delay discharge. This study compared postoperative outcomes after cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) with epidural analgesia versus continuous wound infusion system (CWIS) with/without intraoperative methadone.

METHODS

A single-institution, retrospective chart review was performed including all patients undergoing open CRS/HIPEC from 2018 to 2021. Patient demographics, surgical characteristics, length of stay, and in-hospital analgesic use were reviewed. In-hospital opioid exposure in morphine milligram equivalents (MME) was calculated. Multivariate analysis (MVA) for mean total and daily opioid exposure was conducted.

RESULTS

A total of 157 patients were included. Fifty-three (34%) had epidural analgesia, 96 (61%) had CWIS, and 79 (50%) received methadone. Length of stay was significantly shorter with CWIS + methadone versus epidural (7 vs. 8 days, p < 0.01). MVA showed significantly lower mean total and daily opioid exposure with CWIS+methadone versus epidural (total: 252.8 ± 17.7 MME vs. 486.8 ± 86.6 MME; odds ratio [OR] 0.72, 95% confidence interval [CI] 0.52-0.98, p = 0.04; Daily: 32.8 ± 2.0 MME vs. 51.9 ± 5.7 MME, OR 0.72, 95% CI 0.52-0.99, p ≤ 0.05). The CWIS-only group (n = 17) had a significantly lower median oral opioid exposure versus epidural (135 MME vs. 7.5 MME, p < 0.001) and longer length of stay versus CWIS + methadone (9 vs. 7 days, p = 0.04), There were no CWIS or methadone-associated complications and one epidural abscess.

CONCLUSIONS

CWIS + methadone safely offers better pain control with less in-hospital opioid use, shorter length of stay, and decreased resource utilization compared with epidural analgesia in patients undergoing CRS-HIPEC.

Retrospective Cohort Study of Safety Outcomes Associated with Opioid Rotations to Buprenorphine

The objective of this study was to understand the effect buprenorphine rotations have on respiratory risk and other safety outcomes. This was a retrospective observational study evaluating Veterans who underwent an opioid rotation from full-agonist opioids to buprenorphine products or to alternative opioids. The primary endpoint was change in the Risk Index for Overdose or Serious Opioid-induced Respiratory Depression (RIOSORD) score from baseline to six months post-rotation. Median baseline RIOSORD scores were 26.0 and 18.0 in the Buprenorphine Group and the Alternative Opioid Group, respectively. There was no statistically significant difference between groups in baseline RIOSORD score. At six months post-rotation, median RIOSORD scores were 23.5 and 23.0 in the Buprenorphine Group and Alternative Opioid Group, respectively. The difference in change in RIOSORD scores between groups was not statistically significant (p = 0.23). However, based on changes in RIOSORD risk class, an 11% and 0% decrease in respiratory risk was observed in the Buprenorphine and Alternative Opioid groups, respectively. This finding may be considered clinically significant given a change in risk was observed as predicted by RIOSORD score. Further research is needed to clarify the effect that opioid rotations have on respiratory depression risk and other safety outcomes.

Methadone Potentiates the Cytotoxicity of Temozolomide by Impairing Calcium Homeostasis and Dysregulation of PARP in Glioblastoma Cells

Methadone is commonly used as an alternative to morphine in patients with pain associated with glioblastoma and other cancers. Although concomitant administration of methadone and cytostatics is relatively common, the effect of methadone on the efficacy of cytostatic drugs has not been well studied until recently. Moreover, the mechanism behind the effect of methadone on temozolomide efficacy has not been investigated in previous studies, or this effect has been automatically attributed to opioid receptors. Our findings indicate that methadone potentiates the effect of temozolomide on rat C6 glioblastoma cells and on human U251 and T98G glioblastoma cells and increases cell mortality by approximately 50% via a mechanism of action independent of opioid receptors. Our data suggest that methadone acts by affecting mitochondrial potential, the level of oxidative stress, intracellular Ca²⁺ concentration and possibly intracellular ATP levels. Significant effects were also observed on DNA integrity and on cleavage and expression of the DNA repair protein PARP-1. None of these effects were attributed to the activation of opioid receptors and Toll-like receptor 4. Our results provide an alternative perspective on the mechanism of action of methadone in combination with temozolomide and a potential strategy for the treatment of glioblastoma cell resistance to temozolomide.

Pharmacological interventions for preventing opioid-induced hyperalgesia in adults after opioid-based anesthesia: a systematic review and network meta-analysis

Background: Opioid-induced hyperalgesia (OIH) is an adverse event of prolonged opioid use that increases pain intensity. The optimal drug to prevent these adverse effects is still unknown. We aimed to conduct a network meta-analysis to compare different pharmacological interventions for preventing the increase in postoperative pain intensity caused by OIH. Methods: Several databases were searched independently for randomized controlled trials (RCTs) comparing various pharmacological interventions to prevent OIH. The primary outcomes were postoperative pain intensity at rest after 24 h and the incidence of postoperative nausea and vomiting (PONV). Secondary outcomes included pain threshold at 24 h after surgery, total morphine consumption over 24 h, time to first postoperative analgesic requirement, and shivering incidence. Results: In total, 33 RCTs with 1711 patients were identified. In terms of postoperative pain intensity, amantadine, magnesium sulphate, pregabalin, dexmedetomidine, ibuprofen, flurbiprofen plus dexmedetomidine, parecoxib, parecoxib plus dexmedetomidine, and S (+)-ketamine plus methadone were all associated with milder pain intensity than placebo, with amantadine being the most effective (SUCRA values = 96.2). Regarding PONV incidence, intervention with dexmedetomidine or flurbiprofen plus dexmedetomidine resulted in a lower incidence than placebo, with dexmedetomidine showing the best result (SUCRA values = 90.3). Conclusion: Amantadine was identified as the best in controlling postoperative pain intensity and non-inferior to placebo in the incidence of PONV. Dexmedetomidine was the only intervention that outperformed placebo in all indicators. Clinical Trial Registration: https://www.crd.york.ac. uk/prospero/display_record.php?, CRD42021225361.

Ca2+-Permeable AMPA Receptors Contribute to Changed Dorsal Horn Neuronal Firing and Inflammatory Pain

The dorsal horn (DH) neurons of the spinal cord play a critical role in nociceptive input integration and processing in the central nervous system. Engaged neuronal classes and cell-specific excitability shape nociceptive computation within the DH. The DH hyperexcitability (central sensitisation) has been considered a fundamental mechanism in mediating nociceptive hypersensitivity, with the proven role of Ca²⁺-permeable AMPA receptors (AMPARs). However, whether and how the DH hyperexcitability relates to changes in action potential (AP) parameters in DH neurons and if Ca²⁺-permeable AMPARs contribute to these changes remain unknown. We examined the cell-class heterogeneity of APs generated by DH neurons in inflammatory pain conditions to address these. Inflammatory-induced peripheral hypersensitivity increased DH neuronal excitability. We found changes in the AP threshold and amplitude but not kinetics (spike waveform) in DH neurons generating sustained or initial bursts of firing patterns. In contrast, there were no changes in AP parameters in the DH neurons displaying a single spike firing pattern. Genetic knockdown of the molecular mechanism responsible for the upregulation of Ca²⁺-permeable AMPARs allowed the recovery of cell-specific AP changes in peripheral inflammation. Selective inhibition of Ca²⁺-permeable AMPARs in the spinal cord alleviated nociceptive hypersensitivity, both thermal and mechanical modalities, in animals with peripheral inflammation. Thus, Ca²⁺-permeable AMPARs contribute to shaping APs in DH neurons and nociceptive hypersensitivity. This may represent a neuropathological mechanism in the DH circuits, leading to aberrant signal transfer to other nociceptive pathways.

NMDARs mediate peripheral and central sensitization contributing to chronic orofacial pain

Peripheral and central sensitizations of the trigeminal nervous system are the main mechanisms to promote the development and maintenance of chronic orofacial pain characterized by allodynia, hyperalgesia, and ectopic pain after trigeminal nerve injury or inflammation. Although the pathomechanisms of chronic orofacial pain are complex and not well known, sufficient clinical and preclinical evidence supports the contribution of the N-methyl-D-aspartate receptors (NMDARs, a subclass of ionotropic glutamate receptors) to the trigeminal nociceptive signal processing pathway under various pathological conditions. NMDARs not only have been implicated as a potential mediator of pain-related neuroplasticity in the peripheral nervous system (PNS) but also mediate excitatory synaptic transmission and synaptic plasticity in the central nervous system (CNS). In this review, we focus on the pivotal roles and mechanisms of NMDARs in the trigeminal nervous system under orofacial neuropathic and inflammatory pain. In particular, we summarize the types, components, and distribution of NMDARs in the trigeminal nervous system. Besides, we discuss the regulatory roles of neuron-nonneuronal cell/neuron-neuron communication mediated by NMDARs in the peripheral mechanisms of chronic orofacial pain following neuropathic injury and inflammation. Furthermore, we review the functional roles and mechanisms of NMDARs in the ascending and descending circuits under orofacial neuropathic and inflammatory pain conditions, which contribute to the central sensitization. These findings are not only relevant to understanding the underlying mechanisms, but also shed new light on the targeted therapy of chronic orofacial pain.