A Comparative Study on the Efficacy of Oral Memantine and Placebo for Acute Postoperative Pain in Patients Undergoing Dacryocystorhinostomy (DCR)

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Efficacy of memantine premedication in alleviating postoperative pain- A systematic review and meta-analysis

Many premedication agents with opioid-sparing properties have been used in patients undergoing various elective surgeries. Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist that has been used by many researchers as an opioid-sparing strategy. Various databases like PubMed, Scopus, Cochrane Library, and clinicaltrials.gov were searched after registering the review protocol in PROSPERO for randomized-controlled trials (RCTs) that investigated the efficacy and safety of memantine premedication in adult patients undergoing various elective surgeries. The risk of bias (RoB-2) scale was used to assess the quality of evidence. From the 225 articles that were identified after a database search, 3 studies were included for a qualitative systematic review and a quantitative meta-analysis. The pooled analysis revealed that the use of memantine provided better pain scores at 2nd (mean difference: -0.82, 95% CI: -1.60, -0.05, P = 0.04) with significant heterogeneity (P = 0.06; I² =71%), and 6 hours postoperatively (mean difference: -1.80, 95% CI: -2.23, -1.37, P < 0.00001), but not at 1 hour. The sedation scores at 1 hour were higher in the memantine group but comparable in the 2nd hour. The number of doses of rescue analgesia and nausea/vomiting in the postoperative period was comparable in both groups. The results of this review suggest that memantine premedication could provide better pain scores in the immediate postoperative period with acceptable adverse effects. However, the current evidence is insufficient to suggest the routine use of memantine as a premedication before elective surgeries.

Opioid-Sparing Perioperative Analgesia Within Enhanced Recovery Programs

Opioid-based analgesia in the perioperative period can provide excellent pain control, but this approach exposes the patient to avoidable side effects and possible harm. Optimal analgesia, an approach that targets the fastest functional recovery with adequate pain control while minimizing side effects, can be achieved with opioid minimization. Many different options for nonopioid multimodal analgesia exist and have been shown to be efficacious, with certain modalities being more beneficial for specific surgeries. This review will present the evidence and practical tips for these management strategies.

Comparison of efficacy of gabapentin and memantine premedication in laparoscopic cholecystectomies for postoperative pain relief - A randomised placebo controlled trial

Background and Aims:

The multiplicity of the mechanisms of the pain in laparoscopic cholecystectomy inclines us to the usage of multimodal analgesia. Gabapentin is known for its analgesic efficacy when given as premedication in many surgeries. N-methyl-D-aspartate (NMDA) antagonists are used for both acute and chronic pain, but the use of memantine in the perioperative period is less studied. The aim of this randomised controlled study was to subjectively and objectively compare postoperative pain relief using gabapentin, memantine and placebo as premedication.

Methods:

Sixty-six patients posted for laparoscopic cholecystectomy were randomised into three groups. During the preoperative assessment, the baseline threshold and tolerance values of pain were measured using an algesiometer. Patients were pre-medicated with oral gabapentin 600 mg or memantine 20 mg or placebo an hour before surgery. Following extubation, pain scores were reassessed (both subjectively and objectively) along with Ramsay sedation scores at different time intervals for 4 h postoperatively.

Results:

Gabapentin group had lower Numerical Rating Scale scores at 15 min and 1 h postoperatively when compared to the other two groups. Memantine group had a longer time for the first request for rescue analgesia (50.53 min) compared to gabapentin and placebo. The objective assessment of pain with analgesiometer showed no statistical significance between the three groups for both threshold and tolerance values. Ramsay sedation scores were higher in the gabapentin group compared to the other two.

Conclusion:

Gabapentin provides better postoperative pain relief compared to memantine when given as single dose premedication for laparoscopic cholecystectomy.

Adjuvant Drugs for Peripheral Nerve Blocks: The Role of NMDA Antagonists, Neostigmine, Epinephrine, and Sodium Bicarbonate

The potential for misuse, overdose, and chronic use has led researchers to look for other methods to decrease opioid consumption in patients with acute and chronic pain states. The use of peripheral nerve blocks for surgery has gained increasing popularity as it minimizes peripheral pain signals from the nociceptors of local tissue sustaining trauma and inflammation from surgery. The individualization of peripheral nerve blocks using adjuvant drugs has the potential to improve patient outcomes and reduce chronic pain. The major limitations of peripheral nerve blocks are their limited duration of action and dose-dependent adverse effects. Adjuvant drugs for peripheral nerve blocks show increasing potential as a solution for postoperative and chronic pain with their synergistic effects to increase the duration of action and decrease the required dosage of local anesthetic. N-methyl-d-aspartate (NMDA) receptor antagonists are a viable option for patients with opioid resistance and neuropathic pain due to their affinity to the neurotransmitter glutamate, which is released when patients experience a noxious stimulus. Neostigmine is a cholinesterase inhibitor that exerts its effect by competitively binding at the active site of acetylcholinesterase, which prevents the hydrolysis of acetylcholine and subsequently retaining acetylcholine at the nerve terminal. Epinephrine, also known as adrenaline, can potentially be used as an adjuvant to accelerate and prolong analgesic effects in digital nerve blocks. The theorized role of sodium bicarbonate in local anesthetic preparations is to increase the pH of the anesthetic. The resulting alkaline solution enables the anesthetic to more readily exist in its un-ionized form, which more efficiently crosses lipid membranes of peripheral nerves. However, more research is needed to show the efficacy of these adjuvants for nerve block prolongation as studies have been either mixed or have small sample sizes.

Management of postoperative pain in ophthalmic plastic surgery: a major review

PURPOSE

Clinicians are becoming increasingly aware of the risks of opioid analgesics, and, consequently, are searching for alternatives to these agents. This review considers the existing literature regarding the management of pain after ophthalmic plastic surgery.

METHODS

A literature search was performed through the PubMed database. Articles were assessed for relevance, and the appropriate data was extracted from the medical literature regarding pain management strategies after oculoplastic procedures.

RESULTS

An emerging body of literature suggests the efficacy of a variety of non-narcotic agents in post-operative pain management. Many of these medications prevent the development of pain, and several have been studied in randomized trials. Specifically, pregabalin, ketorolac, acetaminophen, memantine, local anesthetics, and alternative therapies all have documented benefit in this setting.

CONCLUSIONS

Several medications may prevent and treat pain after ophthalmic plastic surgery. These agents are well-tolerated, and many decrease the requirement for opioid analgesics. Clinicians should be aware of these therapies when considering non-narcotic pain management.

Expanding Role of NMDA Receptor Antagonists in the Management of Pain

Pain management is complex regardless of whether the pain is acute or chronic in nature or non-cancer or cancer related. In addition, relatively few pain pharmacotherapy options with adequate efficacy and safety data currently exist. Consequently, interest in the role of NMDA receptor antagonists as a pharmacological pain management strategy has surfaced. This narrative review provides an overview of the NMDA receptor and elaborates on the pharmacotherapeutic profile and pain management literature findings for the following NMDA receptor antagonists: ketamine, memantine, dextromethorphan, and magnesium. The literature on this topic is characterized by small studies, many of which exhibit methodological flaws. To date, ketamine is the most studied NMDA receptor antagonist for both acute and chronic pain management. Although further research about NMDA receptor antagonists for analgesia is needed and the optimal dosage/administration regimens for these drugs have yet to be determined, ketamine appears to hold the most promise and may be of particular value in the perioperative pain management realm.

Efficacy of Preoperative Administration of Acetaminophen and Melatonin on Retrobulbar Block Associated Pain in Cataract Surgery

Background

Retrobulbar block is one of the chosen methods for local anesthesia in cataract surgery. Since it is a painful procedure, using analgesic and sedative drugs is recommended. Current medications have side effects and evaluating of new drugs or new uses of existing safer drugs is necessary.

Objectives

The aim of this study was to compare the administration of melatonin and acetaminophen on pain and hemodynamic changes during retrobulbar block.

Methods

In a double-blinded randomized trial, 180 patients undergoing cataract surgery were randomly divided into three groups: Melatonin group (received melatonin 6 mg), acetaminophen group (received acetaminophen 500 mg), and control group (received placebo). All drugs were administered orally 60 min before arrival to the operating room by nurses blinded to the drugs administered. All patients received fentanyl 0.5 μg/kg before retrobulbar block intravenously. Hemodynamic variables and pain score in each patient were evaluated on arrival in the operating room, during retrobulbar block, during surgery, 20 min after operation, at the end of surgery, and in the recovery room. In case of pain score more than three, additional fentanyl was administered. All data were recorded in structured data sheets.

Results

Data analysis indicated no significant differences among the groups at baseline on any of the demographic variables. Both acetaminophen and melatonin reduced the pain score significantly compared with control during retrobulbar block (P < 0.05 and P < 0.01, respectively). Administration of additional fentanyl was significantly lower in the melatonin group than the control group (P < 0.05). Hemodynamic changes were not significantly different among all groups.

Conclusions

For the first time, as far as we have studied, the analgesic effect of acetaminophen on the retrobulbar block was indicated. We also showed that melatonin can reduce pain during retrobulbar block leading to reduction of additional fentanyl during operation. It seems that both melatonin and acetaminophen may have a beneficial effect on pain control in the retrobulbar block.