Soft drugs in anesthesia: remifentanil as prototype to modern anesthetic drug development

[Remimazolam-Update on basic pharmacologic principles and clinical potential]

In recent years the still relatively new short-acting benzodiazepine remimazolam has been approved and clinically implemented in several countries and regions. Remimazolam is also now approved in the EU and the market launch in Germany is expected in the not too distant future. This is therefore a good point in time to summarize the current evidence for various areas of application, including general anesthesia, sedation and intensive care medicine as well as different dosing schemes.

Remimazolam: its clinical pharmacology and evolving role in anesthesia and sedation practice

PURPOSE OF REVIEW

Remimazolam is a novel benzodiazepine anesthetic/sedative, designed as a rapidly metabolized carboxylic acid. Since its recent launch, the role of remimazolam in modern anesthesia and sedation practice is still evolving. This review aims to outline the clinical pharmacology and clinical utility of remimazolam to elucidate its potential advantages and limitations.

RECENT FINDINGS

Remimazolam is "short-acting" but not ultra-short-acting compared with propofol based on context-sensitive decrement times. But compared to propofol, the availability of the benzodiazepine antagonist, flumazenil, is considered an advantage, particularly in certain emergency situations such as in patients with difficult airways. However, because flumazenil is shorter acting than remimazolam when remimazolam accumulates or is present in a high concentration, the reappearance of remimazolam sedation may occur after the initial reversal of anesthesia/sedation from flumazenil administration. Although it is beneficial that remimazolam causes less respiratory depression and hypotension than propofol, serious respiratory depression and hypotension can still occur. Remimazolam administration causes minimal or no pain on injection. Remimazolam is associated with less postoperative nausea and vomiting than inhaled anesthetics, but propofol is clearly superior in this regard. The anesthetic/sedative effects may be prolonged by severe hepatic impairment; remimazolam tolerance can occur in long-term benzodiazepine users.

SUMMARY

Remimazolam may be beneficial to use in procedural sedation and general anesthesia for patients with difficult airways or hemodynamic instability. Further clinical studies with remimazolam are warranted to identify the potential benefits in other settings and patient populations.

The 50% and 95% effective dose of remimazolam tosilate for anaesthesia induction in sleep disorders patients undergoing laparoscopic cholecystectomy: an up-and-down sequential allocation trial

PURPOSE

Previous reports argue that preoperative sleep conditions of patients can influence the dosage of general anaesthesia drugs. Therefore, we aimed to investigate the dose-effect relationship of preoperative sleep disorders on the induction of general anaesthesia with remimazolam tosilate and calculate the Median effective (ED50) and 95% effective (ED95) dosages.

METHODS

Included in our study were 56 patients who underwent laparoscopic cholecystectomy at our hospital. A separate group of 27 patients with sleep disorders (SD group) and 29 patients without sleep disorders (NSD group) using the Pittsburgh Sleep Quality Index (PSQI) were also included. According to the Dixon 'up-and-down' design, patients received remimazolam at preselected concentrations starting at 0.2 mg/kg. After the administration of remimazolam, loss of consciousness was observed. By observing whether consciousness disappeared within a minute, we adjusted the dose of remimazolam by 0.1 mg/kg (up and down) in the following patient. The Median effective dose (ED50), 95% effective dose (ED95), and 95% confidence interval (CI) of remimazolam for effective sedation were calculated.

RESULTS

The ED50 of remimazolam was 0.226 mg/kg (95%CI 0.221-0.232 mg/kg) in the SD group and 0.191 mg/kg (95%CI, 0.183-0.199 mg/kg) in the NSD group. The ED95 of remimazolam was 0.237 mg/kg (95%CI 0.231-0.262 mg/kg) in the SD group and 0.209 mg/kg (95%CI 0.200-0.254 mg/kg) in the NSD group.

CONCLUSIONS

In the SD group, the ED50 and ED95 of remimazolam during anaesthesia induction were 0.226 and 0.237 mg/kg, respectively. The induction dose of remimazolam in the SD group was significantly higher than that in the NSD group.

Remimazolam: A Retrospective Study of Initial Safety and Recovery Data in Diverse Procedural Sedation

PURPOSE

The new ultra-short-acting benzodiazepine, remimazolam, offers a pharmacokinetic and pharmacodynamic advantage over commonly used procedural sedation medication. This retrospective study explored the real-world utilization of remimazolam during procedural sedation to support the development of a nurse sedation protocol. The primary outcome was to identify associations between recovery time, adverse reactions, and dose-response in expanded patient populations.

METHODS

This study reviewed charts of 292 adult patients from 3 hospitals within one institution who received remimazolam during procedural sedation between June 1, 2021 and December 31, 2021. Data were analyzed using logistic and linear regression.

FINDINGS

The median time to alert in patients receiving remimazolam alone was 12 minutes (interquartile range 10, 17) and increased when additional sedation medications were utilized. Receiving additional sedative medication significantly increased the odds of hypoxia (OR 2.77, 95% CI 1.30-5.91, P = 0.008) after adjusting for body mass index (BMI), American Society of Anesthesiologists physical status (ASA-PS), and total remimazolam dose. There was a 25% increase in odds of experiencing hypoxia for every 5 kg/m2 increase in BMI (95% CI 1.01-1.54, P = 0.037).

IMPLICATIONS

Remimazolam presents as a promising option for nurse procedural sedation, offering minimal impact on hemodynamics and respirations, quick recovery, and no residual sedative effects.

The role and mechanism of esketamine in preventing and treating remifentanil-induced hyperalgesia based on the NMDA receptor-CaMKII pathway

Remifentanil-induced hyperalgesia (RIH) is a common clinical phenomenon that limits the use of opioids in pain management. Esketamine, a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has been shown to prevent and treat RIH. However, the underlying effect mechanism of esketamine on RIH remains unclear. This study aimed to investigate the role and mechanism of esketamine in preventing and treating RIH based on the NMDA receptor-CaMKIIα pathway. In this study, an experimental animal model was used to determine the therapeutic effect of esketamine on pain elimination. Moreover, the mRNA transcription and protein expression levels of CaMKII and GluN2B were investigated to offer evidence of the protective capability of esketamine in ameliorating RIH. The results demonstrated that esketamine attenuated RIH by inhibiting CaMKII phosphorylation and downstream signaling pathways mediated by the NMDA receptor. Furthermore, ketamine reversed the upregulation of spinal CaMKII induced by remifentanil. These findings suggest that the NMDA receptor-CaMKII pathway plays a critical role in the development of RIH, and ketamine's effect on this pathway may provide a new therapeutic approach for the prevention and treatment of RIH.

Clinical Trial Comparing Remimazolam with Propofol During Intravenous Anesthesia: A Prospective Randomised Clinical Trial

BACKGROUND AND OBJECTIVE

Remimazolam is a water-soluble sedative-anesthetic with short-acting properties and less hemodynamic effects. Currently, it is primarily used for gastroenteroscopy sedation.

AIM

The aim of this study is to investigate the effectiveness and safety of Remimazolam as an alternative intravenous anesthetic agent in surgical patients, in order to expand clinical options beyond Propofol.

METHODS

Eighty patients aged 20-69 and classified as an American Society of Anesthesiologists physical status I-II were randomly assigned to either the Remimazolam group (RM group) or the Propofol group (PR group) for anesthesia induction and maintenance. Hemodynamics and Bispectral Index (BIS) were recorded before and after anesthesia, along with other relevant indices such as the time, to loss of consciousness (LoC), operation time, anesthesia time, awakening time, the number of cases of injection site pain. Additionally, the Ramsay sedation score, intraoperative awareness, dreaming, and postoperative adverse events were also assessed.

RESULTS

After anesthesia, both groups experienced a significant decrease in blood pressure compared to baseline values, however, the reduction in blood pressure was less significant in the RM group than in the PR group (P<0.05). The heart rate of patients in the RM group remained relatively stable at all time points. There were significantly more cases of injection site pain and use of pressor or atropine during operation observed in the PR group compared to the RM group (P<0.05). There were no significant differences between the two groups in terms of time to loss of consciousness, anesthesia time, operation time, awakening time, and intraoperative awareness (P>0.05). However, at 5 and 30 minutes after awakening, the Ramsay sedation score was significantly better in the RM group compared to the PR group (P<0.05).

CONCLUSION

When remimazolam is used for intravenous anesthesia induction and maintenance, it can achieve a favorable anesthetic effect while maintaining a relatively stable blood pressure and heart rate. Patients experience shorter awakening times (8.3±3.7 min), better awakening quality (5 min Ramsay sedation score is 2 points), and no intraoperative awareness.

Efficacy and safety of remimazolam-based sedation for intensive care unit patients undergoing upper gastrointestinal endoscopy: a cohort study

BACKGROUND

Remimazolam is a novel ultra-short-acting sedative, but its safety and adverse events (AEs) in high-risk patients in the intensive care unit (ICU) setting remain unknown.

METHODS

This was a single-center, retrospective study that compared remimazolam to propofol and midazolam in patients undergoing upper gastrointestinal endoscopy. The primary outcome was the incidence of treatment-related AEs. The secondary outcomes were the time to extubation, the length of ICU stay, and the average cost of sedative per case.

RESULTS

Of the 88 patients analyzed, 47 were treated with remimazolam (mean dose, 7.90±4.84 mg), and 41 were treated with propofol (21.19±17.98 mg) or midazolam (3.08±2.17 mg). There was no statistically significant difference in the average duration of the endoscopic procedure (35.89±13.37 min vs. 44.51±21.68 min, P=0.133) or the time to extubation (15.00±9.75 h vs. 20.59±18.71 h, P=0.211) in the remimazolam group (group I) compared to the propofol or midazolam group (group II). ICU stays (5.40±2.93 d vs. 4.63±3.31 d, P=0.072) and treatment-related AEs (48.61% vs. 51.38%, P=0.056) were similar between groups. The average cost of sedative per case was significantly lower in the group I than in the group II (RMB 16.07±10.58 yuan vs. RMB 24.37±15.46 yuan, P=0.016).

CONCLUSION

Remimazolam-based sedation was noninferior to the classic sedatives and had lower average cost per case, indicating that it may be used as a promising sedative for high-risk patients during endoscopic procedures in the ICU setting.

The Effect of Propofol plus Remifentanil for PostoperativePain and Heart Rate Management in Patients Undergoing Abdominal Hysterectomy

Purpose

To explore the effect of propofol plus remifentanil for postoperative pain and heart rate management in patients undergoing abdominal hysterectomy.

Methods

In this prospective randomized controlled study, 96 patients who underwent abdominal hysterectomy in an affiliated hospital of Fujian Medical University from April 2016 to April 2017 were recruited and randomized into the study group (n = 48) and control group (n = 48) via the random number table method. The control group received remifentanil for anesthesia, and the study group was given propofol plus remifentanil. The postoperative pain and heart rates of patients were compared between the two groups.

Results

No significant difference was observed in the heart rate and adrenaline values between the two groups before anesthesia, and the study group had significantly lower adrenaline values and heart rates intraoperatively and 15 min after operation than the control group. Patients in the study group showed shorter time-lapse before independent breathing recovery, extubation, and resuscitation compared to those in the control group. The study group received less patient-controlled intravenous analgesia (PCIA) as compared to the study group within 48 h after operation. In the study group, the numeric rating scale (NRS) scores within 1 h, 2 h, 6 h, 8 h, and 12 h after operation were significantly lower than those in the control group (P < 0.001). Propofol plus remifentanil offer a viable alternative for postoperative pain management and stress alleviation after abdominal hysterectomy with a high safety profile. Further clinical trials are, however, required prior to clinical promotion.

Structural Modification in Anesthetic Drug Development for Prodrugs and Soft Drugs

Among the advancements in drug structural modifications, the increased focus on drug metabolic and pharmacokinetic properties in the anesthetic drug design process has led to significant developments. Drug metabolism also plays a key role in optimizing the pharmacokinetics, pharmacodynamics, and safety of drug molecules. Thus, in the field of anesthesiology, the applications of pharmacokinetic strategies are discussed in the context of sedatives, analgesics, and muscle relaxants. In this review, we summarize two approaches for structural optimization to develop anesthetic drugs, by designing prodrugs and soft drugs. Drugs that both failed and succeeded during the developmental stage are highlighted to illustrate how drug metabolism and pharmacokinetic optimization strategies may help improve their physical and chemical properties.

A population pharmacokinetic model of remimazolam for general anesthesia and consideration of remimazolam dose in clinical practice

BACKGROUND

Remimazolam besylate is a novel short-acting benzodiazepine. An appropriate pharmacokinetic model of remimazolam is desirable in anesthesia practice. The aim of the study was to develop a pharmacokinetic model using plasma samples from patients anesthetized with remimazolam. Influence of patient characteristics, context-sensitive decrement-times, and dose regimens were also examined.

METHODS

Data were obtained from four trials on patients, and seven trials on healthy volunteers. The characteristics of 416 male and 246 female subjects were as follows: age, 18-93 years; body weight, 34-149 kg; and American Society of Anesthesiologists physical status (ASA-PS), I-IV. 2231 arterial and 3200 venous samples were used for the final model. The equilibration rate constant between arterial plasma and effect-site was estimated using the concept of time to peak effect. The final model was used to generate context-sensitive decrement times and dose regimens for general anesthesia.

RESULTS

A three-compartment model plus virtual venous compartment with allometric scaling of adjusted body weight (ABW), age, sex, and ASA-PS as covariates were selected as the final model. Elimination clearance was lower in males, and in subjects with higher ABW and ASA-PS scores. Approximately 10% or 20% higher dose rate was necessary in females than in males or ASA-PS I/II than III/IV patient. The context-sensitive half-time for effect-site concentration in a 55-year-old, 70-kg, 170-cm male or female ASA-PS I/II patient after > 6-h infusion was 16.7 or 15.9 min.

CONCLUSION

Remimazolam pharmacokinetic model for general anesthesia was successfully developed. ABW, ASA-PS, and sex has a considerable impact on the remimazolam concentration.

Review of remimazolam and sedatives in the intensive care unit

Remimazolam is a novel intravenous ultra-short acting benzodiazepine that has the potential of being a safe and effective new sedative for use in intensive care unit (ICU) settings. Because remimazolam metabolizes rapidly by being hydrolyzed to an inactive metabolite (CNS 7054) through non-specific tissue esterase activity, specific dosing adjustment for older adults and for patients with renal or hepatic impairment patients (except for those with severe hepatic impairment) is not required. In addition, research has shown that remimazolam may be reversed by administration of flumazenil, as its half time was sufficiently short compared to flumazenil. It shows a lower incidence of cardiorespiratory depression, less injection pain, and no fatal complications such as propofol infusion syndrome and malignant hyperthermia of inhalational anesthetics. Future studies to study the suitability of remimazolam for managing the sedation of ICU patients who need sedation for a long time over several days is required.

Remimazolam - current knowledge on a new benzodiazepine intravenous anesthetic agent

Intravenous anesthetic agents such as midazolam, propofol, and ketamine are routinely used to provide anesthesia and sedation. They have been shown to effectively induce and maintain amnesia, sedation, and hypnosis in various patient groups and clinical settings. However, all anesthetic agents have the potential to cause unwanted side effects such as hemodynamic instability, respiratory depression, or slow recovery due to prolonged post-procedural sedation. Remimazolam, a recently approved benzodiazepine for general anesthesia and procedural sedation in Korea, has been successfully used for these purposes. To date, inconclusive knowledge has been obtained regarding the use of remimazolam in different patient populations and under various surgical conditions. With respect to the specific pharmacokinetic and pharmacodynamic characteristics of remimazolam, the use of remimazolam is expected to increase providing safe general anesthesia and sedation. This review aims to provide an overview of the basic and clinical pharmacology of remimazolam and to compare it with midazolam and propofol.

The Role of Pharmacogenomics in Postoperative Pain Management

Pharmacogenomics can improve pain management by considering individual variations in pain perception and susceptibility and sensitivity to medicines related to genetic diversity. Due to the subjective nature of pain and the fact that people respond differently to medicines, it can be challenging to develop a consistent and successful regimen for pain disorders. Numerous factors influence the outcome of pain treatment programs, but two stand out: altered perception of pain and varying responsiveness to analgesic medicines. Numerous polymorphisms in genes such as CYP2D6, OPRM1, and ABCB1 have been identified, culminating in a heterogeneous response to pain medication in people who have these genetic polymorphisms. Improved treatment regimens that factor in pharmacogenetic differences in patients would help reduce the risk of opioid dependency and help effectively treat postoperative pain.

A comprehensive review of remimazolam for sedation

Benzodiazepines are one of the most commonly used medications in the field of anesthesia. They offer excellent anxiolytic and amnestic properties ideal for the perioperative period when patient anxiety is understandably heightened. Remimazolam has presented a favorable alternative to some of the common intravenous anesthetic agents used given its fast onset of action, high safety profile, and reasonably short duration of action. The drugs within the four classes of benzodiazepines, 2-keto-benzodiazepines, 3-hydroxy-benzodiazepines, triazolo-benzodiazepines, and 7-nitro-benzodiazepines provide varying degrees of anxiolysis, sedation, and amnesia. This is provided by the benzodiazepine molecule binding and causing a conformational change to the chloride ion channel to cause hyperpolarization and thus inhibition of the central nervous system. Each type of benzodiazepine has a preferred role within the realm of medicine. For instance, diazepam is used for the treatment of seizures and anxiety. Midazolam's anxiolytic and anterograde amnestic properties are taking advantage of during the perioperative period. Lorazepam is beneficial for anxiety and status epilepticus. Remimazolam, currently in phase II and III clinical trials, has demonstrated a very short during of action and low context-sensitive half-time, allowing for its rapid removal even during a prolonged infusion. Much of its properties may be credited to being a soft drug, meaning it is a metabolically active drug that is rapidly inactivated in the body. This provides anesthesiologists and other practitioners administering it with a more predictable sedative. These properties have the potential to push it towards becoming the drug of choice for premedication during the perioperative period and sedation in the ICU. Furthermore, remimazolam does not seem to rely on any specific organ to be metabolized. The drug's ester moiety makes it a substrate for non-specific tissue esterase enzymes, meaning its metabolism and elimination are not impaired in patients with hepatic and/or renal disease. Its addictive potential closely resembles that of its parent compound, midazolam. Reports of its adverse reactions include headache and somnolence after an involuntary movement during infusion. Benzodiazepines are a great adjunct to anesthetic care. Remimazolam's safety profile, pharmacokinetics, pharmacodynamics, and potential practical use make it quite favorable in this regard. It has the potential to equip anesthesiologists and other medical practitioners with a more predictable medication that has a good safety profile. However, further large clinical trials will provide us with a better understanding of the advantages and disadvantages of remimazolam.

Remimazolam: Non-Clinical and Clinical Profile of a New Sedative/Anesthetic Agent

A program to identify novel intravenous sedatives with a short and predictable duration of action was initiated in the late 1990's by Glaxo Wellcome. The program focussed on the identification of ester-based benzodiazepine derivatives that are rapidly broken down by esterases. Remimazolam was identified as one of the lead compounds. The project at Glaxo was shelved for strategic reasons at the late lead optimization stage. Via the GSK ventures initiative, the program was acquired by the small biotechnology company, TheraSci, and, through successive acquisitions, developed as the besylate salt at CeNeS and PAION. The development of remimazolam besylate has been slow by industry standards, primarily because of the resource limitations of these small companies. It has, however, recently been approved for anesthesia in Japan and South Korea, procedural sedation in the United States, China, and Europe, and for compassionate use in intensive care unit sedation in Belgium. A second development program of remimazolam was later initiated in China, using a slightly different salt form, remimazolam tosylate. This salt form of the compound has also recently been approved for procedural sedation in China. Remimazolam has the pharmacological profile of a classical benzodiazepine, such as midazolam, but is differentiated from other intravenous benzodiazepines by its rapid conversion to an inactive metabolite resulting in a short onset/offset profile. It is differentiated from other intravenous hypnotic agents, such as propofol, by its low liability for cardiovascular depression, respiratory depression, and injection pain. The benzodiazepine antagonist flumazenil can reverse the effects of remimazolam in case of adverse events and further shorten recovery times. The aim of this review is to provide an analysis of, and perspective on, published non-clinical and clinical information on 1) the pharmacology, metabolism, pharmacokinetics, and pharmacodynamic profile of remimazolam, 2) the profile of remimazolam compared with established agents, 3) gaps in the current understanding of remimazolam, 4) the compound's discovery and development process and 5) likely future developments in the clinical use of remimazolam.

Emerging Approaches in Intravenous Moderate and Deep Sedation

Successful pharmacological innovations that have made a difference in daily practice are rare in the world of anesthesia and sedation. After many years of research, it seems that we finally have two new drug innovations that are likely to change the paradigm of moderate and deep sedation. These are oliceridine and remimazolam. Both have been in development for over a decade. Oliceridine was synthesized in a lab as an entirely new molecule. It is a biased μ- receptor agonist that acts preferentially on the G-protein pathway (which is responsible for analgesia). At least in lower doses, it has minimal effect on the beta-arrestin pathway, which is responsible for unwanted effects of μ-opioid receptor activation such as respiratory depression and gastrointestinal dysfunction. Like any other μ- receptor agonist, it produces appropriate dose-dependent analgesia. Remimazolam is structurally similar to midazolam; however, it has an additional ester linkage that delivers the kinetics of remifentanil. As a result, while pharmacodynamically identical to midazolam, remimazolam is metabolized by ester hydrolysis and subsequently its elimination is rapid and predictable. The present review discusses the two drugs in detail with a particular emphasis on their potential role in moderate and deep sedation.