Does Fentanyl Lead to Opioid-induced Hyperalgesia in Healthy Volunteers?

Rationale for and approach to preoperative opioid weaning: a preoperative optimization protocol

The practice of chronic opioid prescription for chronic non-cancer pain has come under considerable scrutiny within the past several years as mounting evidence reveals a generally unfavorable risk to benefit ratio and the nation reels from the grim mortality statistics associated with the opioid epidemic. Patients struggling with chronic pain tend to use opioids and also seek out operative intervention for their complaints, which combination may be leading to increased postoperative "acute-on-chronic" pain and fueling worsened chronic pain and opioid dependence. Besides worsened postoperative pain, a growing body of literature, reviewed herein, indicates that preoperative opioid use is associated with significantly worsened surgical outcomes, and severely increased financial drain on an already severely overburdened healthcare budget. Conversely, there is evidence that preoperative opioid reduction may result in substantial improvements in outcome. In the era of accountable care, efforts such as the Enhanced Recovery After Surgery (ERAS) protocol have been introduced in an attempt to standardize and facilitate evidence-based perioperative interventions to optimize surgical outcomes. We propose that addressing preoperative opioid reduction as part of a targeted optimization approach for chronic pain patients seeking surgery is not only logical but mandatory given the stakes involved. Simple opioid reduction/abstinence however is not likely to occur in the absence of provision of viable and palatable alternatives to managing pain, which will require a strong focus upon reducing pain catastrophization and bolstering self-efficacy and resilience. In response to a call from our surgical community toward that end, we have developed a simple and easy-to-implement outpatient preoperative optimization program focusing on gentle opioid weaning/elimination as well as a few other high-yield areas of intervention, requiring a minimum of resources.

TRV0109101, a G Protein-Biased Agonist of the µ-Opioid Receptor, Does Not Promote Opioid-Induced Mechanical Allodynia following Chronic Administration

Prescription opioids are a mainstay in the treatment of acute moderate to severe pain. However, chronic use leads to a host of adverse consequences including tolerance and opioid-induced hyperalgesia (OIH), leading to more complex treatment regimens and diminished patient compliance. Patients with OIH paradoxically experience exaggerated nociceptive responses instead of pain reduction after chronic opioid usage. The development of OIH and tolerance tend to occur simultaneously and, thus, present a challenge when studying the molecular mechanisms driving each phenomenon. We tested the hypothesis that a G protein-biased µ-opioid peptide receptor (MOPR) agonist would not induce symptoms of OIH, such as mechanical allodynia, following chronic administration. We observed that the development of opioid-induced mechanical allodynia (OIMA), a model of OIH, was absent in β-arrestin1-/- and β-arrestin2-/- mice in response to chronic administration of conventional opioids such as morphine, oxycodone and fentanyl, whereas tolerance developed independent of OIMA. In agreement with the β-arrestin knockout mouse studies, chronic administration of TRV0109101, a G protein-biased MOPR ligand and structural analog of oliceridine, did not promote the development of OIMA but did result in drug tolerance. Interestingly, following induction of OIMA by morphine or fentanyl, TRV0109101 was able to rapidly reverse allodynia. These observations establish a role for β-arrestins in the development of OIH, independent of tolerance, and suggest that the use of G protein-biased MOPR ligands, such as oliceridine and TRV0109101, may be an effective therapeutic avenue for managing chronic pain with reduced propensity for opioid-induced hyperalgesia.

Ketamine Infusion as a Counter Measure for Opioid Tolerance in Mechanically Ventilated Children: A Pilot Study

BACKGROUND

Drug rotation to prevent opioid tolerance is well recognized in chronic pain management. However, ketamine infusion as a counter measure for opioid tolerance is rarely described in mechanically ventilated children developing tolerance from prolonged opioid infusion.

PATIENTS AND METHODS

We performed a retrospective study in a 14-bed medical-surgical-cardiac pediatric intensive care unit. Thirty-two mechanically ventilated children who had developed tolerance from prolonged intravenous infusion of opioids received a continuous intravenous infusion of ketamine as an opioid substitute for more than 2 days, scheduled in a drug rotation protocol.

RESULTS

Thirty-two children (median age 2.5 years, range 0.1-16.0; weight 11.2 kg [3.8-62.0]) were included. Patients had received continuous intravenous infusion of opioids and benzodiazepines for 16.0 days (4.0-34.0) when drug rotation was started. The median dose of continuous intravenous infusion of ketamine was 4.0 mg·kg^-1·h^-1 (1.8-6.0) and the median duration was 3.0 days (2.0-6.0). After having restarted opioids, fentanyl doses were significantly lower compared with the time before the drug rotation began (after, 2.9 µg·kg^-1·h^-1 [0.8-4.9] vs before, 4.15 µg·kg^-1·h^-1 [1.2-10.0]; p < 0.001). Continuous intravenous infusion of midazolam and clonidine were unchanged during drug rotation. COMFORT-B scoring was significantly lower after having started drug rotation (after, 14.5 [8-19] vs before, 16 [11-22]; p < 0.001).

CONCLUSION

Drug rotation with ketamine in mechanically ventilated children with opioid tolerance is feasible and seems to reduce the rate of fentanyl infusion.

CaMKIIα may modulate fentanyl-induced hyperalgesia via a CeLC-PAG-RVM-spinal cord descending facilitative pain pathway in rats

Each of the lateral capsular division of central nucleus of amygdala(CeLC), periaqueductal gray (PAG), rostral ventromedial medulla(RVM) and spinal cord has been proved to contribute to the development of opioid-induced hyperalgesia(OIH). Especially, Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα) in CeLC and spinal cord seems to play a key role in OIH modulation. However, the pain pathway through which CaMKIIα modulates OIH is not clear. The pathway from CeLC to spinal cord for this modulation was explored in the present study. Mechanical and thermal hyperalgesia were tested by von Frey test or Hargreaves test, respectively. CaMKIIα activity (phospho-CaMKIIα, p-CaMKIIα) was evaluated by western blot analysis. CaMKIIα antagonist (KN93) was micro-infused into CeLC, spinal cord or PAG, respectively, to evaluate its effect on behavioral hyperalgesia and p-CaMKIIα expression in CeLC, PAG, RVM and spinal cord. Then the underlying synaptic mechanism was explored by recording miniature excitatory postsynaptic currents (mEPSCs) on PAG slices using whole-cell voltage-clamp methods. Results showed that inhibition of CeLC, PAG or spinal CaMKIIα activity respectively by KN93, reversed both mechanical and thermal hyperalgesia. Microinjection of KN93 into CeLC decreased p-CaMKIIα expression in CeLC, PAG, RVM and spinal cord; while intrathecal KN93 can only block spinal but not CeLC CaMKIIα activity. KN93 injected into PAG just decreased p-CaMKIIα expression in PAG, RVM and spinal cord, but not in the CeLC. Similarly, whole-cell voltage-clamp recording found the frequency and amplitude of mEPSCs in PAG cells were decreased by KN93 added in PAG slice or micro-infused into CeLC in vivo. These results together with previous findings suggest that CaMKIIα may modulate OIH via a CeLC-PAG-RVM-spinal cord descending facilitative pain pathway.

Virtual reality distraction decreases routine intravenous sedation and procedure-related pain during preoperative adductor canal catheter insertion: a retrospective study

Background

Virtual reality (VR) distraction is a nonpharmacological method to prevent acute pain that has not yet been thoroughly explored for anesthesiology. We present our experience using VR distraction to decrease routine intravenous sedation for patients undergoing preoperative perineural catheter insertion.

Methods

This 1-month quality improvement project involved all elective unilateral primary total knee arthroplasty patients who received a preoperative adductor canal catheter. Clinical data were analyzed retrospectively. For the first half of the month, all patients received usual care; intravenous sedation was administered at the discretion of the regional anesthesiologist. For the second half of the month, patients were offered VR distraction with intravenous sedation upon request. The primary outcome was fentanyl dosage; other outcomes included midazolam dosage, procedure-related pain, procedural time, and blood pressure changes.

Results

Seven patients received usual care and seven used VR. In the VR group, 1/7 received intravenous sedation versus 6/7 who received usual care (P = 0.029). The fentanyl dose was lower (median [10th–90th percentiles]) in the VR group (0 [0–20] µg) versus the non-VR group (50 [30–100] µg; P = 0.008). Midazolam use was lower in the VR group (0 [0–0] mg) than in the non-VR group (1 [0–1] mg; P = 0.024). Procedure-related pain was lower in the VR group (1 [1–4] NRS) versus the non-VR group (3 [2–6] NRS; P = 0.032). There was no difference in other outcomes.

Conclusions

VR distraction may provide an effective nonpharmacological alternative to intravenous sedation for the ultrasound-guided placement of certain perineural catheters.

Not so patchy story of attempted suicide…leading to 24 hours of deep sleep and survival!

Here, we present a somewhat unusual suicide attempt where, despite an unbelievable overdose with transdermal fentanyl patches, the patient survived. The patient-a woman aged 70 years, who has suffered from chronic back pain despite starting transdermal fentanyl patches in 2007. The unconventional method of attempted suicide was based on online research into deaths from fentanyl patch toxicity. She had gradually accumulated 100 µg fentanyl patches from repeat prescriptions, applying 14 patches with fatal intent, alongside 2 45 mg mirtazapine tablets, and concurrent therapeutic doses of tramadol and morphine sulfate oral solution. However, after 24 hours, she awoke from a deep sleep to the sound of the telephone ringing, somewhat amazed her drastic efforts had failed. During admission to Great Western hospital, she was seen by liaison psychiatry and subsequently transferred to the care of the pain management team, to which she had already been referred.

Opioid-induced hyperalgesia: Cellular and molecular mechanisms

Opioids produce strong analgesia but their use is limited by a paradoxical hypersensitivity named opioid-induced hyperalgesia (OIH) that may be associated to analgesic tolerance. In the last decades, a significant number of preclinical studies have investigated the factors that modulate OIH development as well as the cellular and molecular mechanisms underlying OIH. Several factors have been shown to influence OIH including the genetic background and sex differences of experimental animals as well as the opioid regimen. Mu opioid receptor (MOR) variants and interactions of MOR with different proteins were shown important. Furthermore, at the cellular level, both neurons and glia play a major role in OIH development. Several neuronal processes contribute to OIH, like activation of neuroexcitatory mechanisms, long-term potentiation (LTP) and descending pain facilitation. Increased nociception is also mediated by neuroinflammation induced by the activation of microglia and astrocytes. Neurons and glial cells exert synergistic effects, which contribute to OIH. The molecular actors identified include the Toll-like receptor 4 and the anti-opioid systems as well as some other excitatory molecules, receptors, channels, chemokines, pro-inflammatory cytokines or lipids. This review summarizes the intracellular and intercellular pathways involved in OIH and highlights some mechanisms that may be challenged to limit OIH in the future.

Opioid-induced redistribution of 6TM and 7TM μ opioid receptors: A hypothesized mechanistic facilitator model of opioid-induced hyperalgesia

Opioids are still the most popular form of pain treatment, but many unavoidable side effects make opioids a big challenge in effective pain management. Opioid-induced hyperalgesia (OIH), a paradoxical phenomenon, portrays an increased sensitivity to harmful stimuli caused by opioid exposure. Changes in the neural modulation are considered a major contributor to the development of OIH. Activation of opioid receptors (ORs) and corresponding downstream molecules are the vital composition of functional performance of opioids. Increasing interests were proposed of the interaction between ORs and other neural transmitter systems such as glutamatergic, GABAergic and adrenergic ones to the genesis of OIH. G protein coupled μ-opioid receptor (MOR) was studied comprehensively on its role in the development of OIH. In addition to the relationship between MOR and other neurotransmitter receptors, a new intracellular MOR that has six transmembrane (6TM) domains was identified, and found to perform a pro-nociceptive task in contrast to the counterpart 7TM isoform. A mechanistic model of OIH in which both 6TM and 7TM MORs undergoing membrane redistribution upon opioid exposure is proposed which eventually facilitates the neurons more sensitive to nociceptive stimulation than that of the preceding opioid exposure.