Pharmacodynamics and pharmacokinetics of intramuscular dexmedetomidine

Analgesic Effects of Ropivacaine Combined With Dexmedetomidine in Transversus Abdominis Plane Block in Patients Undergoing Laparoscopic Cholecystectomy: A Systematic Review and Meta-analysis

PURPOSE

This review aimed to conduct a meta-analysis of published randomized controlled studies (RCTs) comparing the effectiveness of dexmedetomidine (DEX) combined with ropivacaine versus single ropivacaine in transversus abdominis plane block (TAPB) for postoperative analgesia after laparoscopic cholecystectomy (LC). The purpose was to investigate whether DEX combined with ropivacaine in TAPB for postoperative analgesia in LC is superior to single ropivacaine administration.

DESIGN

A Systematic Review and Meta-analysis.

METHODS

Five electronic database systems were searched for RCTs on the effects of DEX combined with ropivacaine (joint group) and single ropivacaine on postoperative analgesia in LC. The standardized mean difference (SMD) or odds ratio (OR) and their corresponding 95% confidence interval (CI) of the indicators were calculated for comparison.

FINDINGS

As of December 23, 2021, 153 articles were retrieved, but only 16 articles were finally included in this meta-analysis. The results showed that compared with single ropivacaine, DEX combined with ropivacaine in TAPB had better analgesia and lighter sedative effect in patients after LC. After LC 2h(T1), 4h(T2), 8h(T3), 12h(T4) and 24h (T5), the joint group participants have lower VAS scores (T1: SMD = -0.32, 95%CI: -0.49, -0.14; T2: SMD = -1.11, 95%CI: -1.56, -0.65; T3: SMD = -2.88, 95%CI: -3.74, -2.02; T4: SMD = -2.56, 95%CI: -3.04, -2.08; T5: SMD = -1.44, 95%CI: -1.81, -1.06). Also, the Ramsay score of the joint group is higher than the single group (T1: SMD = 1.05, 95%CI: 0.39, 1.71; T2: SMD = 1.57, 95%CI: 0.57, 2.57; T3: SMD = 1.64, 95%CI: 0.65, 2.63; T4: SMD = 1.72, 95%CI: 0.54, 2.89; T5: SMD = 0.57, 95%CI: 0.21, 0.94).

CONCLUSIONS

The results of this review and meta-analysis suggest that DEX combined with ropivacaine has less postoperative pain, more patients got the status of sober and cooperative, and longer postoperative analgesia lasted than ropivacaine alone in TAPB, especially in the group of combined treatment with 1.0 mcg/kg DEX. Furthermore, the flow dynamics of the two groups are stable, and there is no notable difference in the incidence of adverse reactions.

Retrospective Comparison of Intramuscular Admixtures of Ketamine and Dexmedetomidine Versus Ketamine and Midazolam for Preoperative Sedation

Precooperative children and patients with intellectual disabilities often require intramuscular (IM) sedation prior to the induction of general anesthesia (GA). Ketamine is an effective preinduction sedative but can produce significant adverse side effects. Dexmedetomidine, a sedative with sympatholytic and analgesic properties, may provide advantages when used in combination with ketamine. This retrospective study evaluated the efficacy and safety of IM ketamine with dexmedetomidine for preoperative sedation. We conducted a chart review of all patients (n = 105) treated for dental rehabilitation who received either IM ketamine and dexmedetomidine (study group, n = 74) or IM ketamine and midazolam (control group, n = 31) prior to induction of GA. No significant difference (p = .14) was observed in the time interval from IM administration to operating room entry (median [interquartile range]) between the study and control groups (5 [4-8] vs 5 [2-7] minutes). Patients who received IM dexmedetomidine exhibited significantly lower mean arterial pressures throughout the induction (p = .004) and had lower heart rates (p = .01) throughout the intraoperative period compared with patients who did not receive dexmedetomidine. The combination of dexmedetomidine and ketamine may provide effective and safe IM sedation prior to the induction of GA.

Intramuscular dexmedetomidine and oral chloral hydrate for pediatric sedation for electroencephalography: A propensity score-matched analysis

BACKGROUND

Intramuscular dexmedetomidine can be used for pediatric sedation without requiring intravenous access and has advantages for electroencephalography by inducing natural sleep pathway, but only a limited number of studies compared the efficacy of intramuscular dexmedetomidine with oral chloral hydrate.

AIMS

To compare the efficacy and safety of intramuscular dexmedetomidine and oral chloral hydrate used for sedation during electroencephalography in pediatric patients.

METHODS

We reviewed the medical records of pediatric patients who underwent sedation for electroencephalography between January 2015 and December 2016. Initial doses of dexmedetomidine and chloral hydrate were 3 mcg/kg and 50 mg/kg, respectively; second doses (1 mcg/kg and 50 mg/kg, respectively) were administered if adequate sedation was not achieved. Demographic data, time of sedative administration, time of sedation and awakening, and time of arrival at recovery room and discharge were analyzed.

RESULTS

Out of a total of 1239 patients, 125 patients had received dexmedetomidine and 1114 had received chloral hydrate. After 1:1 propensity score matching, the dexmedetomidine and chloral hydrate groups each had 118 patients. Testing completion rate with a single dose of medication was higher in the dexmedetomidine group (91.5% vs 71.2%; mean difference [95% CI] 20.3 [10.8-29.9]; P < .0001; Pearson chi-square value = 16.09). Sedation onset time was shorter in the dexmedetomidine group as well (16.6 ± 13.0 minutes vs 41.5 ± 26.8 minutes; mean difference [95% CI] 24.8 [19.1-30.6]; P < .0001; T = 8.27). On the contrary, the duration of recovery was longer in the dexmedetomidine group (35.5 ± 40.2 minutes vs 18.5 ± 30.7 minutes; mean difference [95% CI] 18.6 [8.8-28.5]; P = .0002; T = -2.82). Total residence time was not significantly different between the two groups (125.8 ± 40.6 minutes vs 122.1 ± 42.2 minutes, mean difference [95% CI] 5.21 [6.1-16.5], P = .3665 T = 0.04).

CONCLUSIONS

Intramuscular dexmedetomidine showed higher sedation success rate and shorter time to achieving the desired sedation level compared with oral chloral hydrate and thus may be an effective alternative for oral chloral hydrate in pediatric patients requiring sedation for electroencephalography.

Dexmedetomidine in Enhanced Recovery After Surgery (ERAS) Protocols for Postoperative Pain

PURPOSE OF REVIEW

Effective acute pain management has evolved considerably in recent years and is a primary area of focus in attempts to defend against the opioid epidemic. Persistent postsurgical pain (PPP) has an incidence of up to 30-50% and has negative outcome of quality of life and negative burden on individuals, family, and society. The 2016 American Society of Anesthesiologists (ASA) guidelines states that enhanced recovery after surgery (ERAS) forms an integral part of Perioperative Surgical Home (PSH) and is now recommended to use a multimodal opioid-sparing approach for management of postoperative pain. As such, dexmedetomidine is now being used as part of ERAS protocols along with regional nerve blocks and other medications, to create a satisfactory postoperative outcome with reduced opioid consumption in the Post anesthesia care unit (PACU).

RECENT FINDINGS

Dexmedetomidine, a selective alpha2 agonist, possesses analgesic effects and has a different mechanism of action when compared with opioids. When dexmedetomidine is initiated at the end of a procedure, it has a better hemodynamic stability and pain response than ropivacaine. Dexmedetomidine can be used as an adjuvant in epidurals with local anesthetic sparing effects. Its use during nerve blocks results in reduced postoperative pain. Also, local infiltration of IV dexmedetomidine is associated with earlier discharge from PACU. Perioperative use of dexmedetomidine has significantly improved postoperative outcomes when used as part of ERAS protocols. An in-depth review of the use of dexmedetomidine in ERAS protocols is presented for clinical anesthesiologists.

Subcutaneously administered dexmedetomidine is efficiently absorbed and is associated with attenuated cardiovascular effects in healthy volunteers

PURPOSE

Palliative care patients often need sedation to alleviate intractable anxiety, stress, and pain. Dexmedetomidine is used for sedation of intensive care patients, but there is no prior information on its subcutaneous (SC) administration, a route that would be favored in palliative care. We compared the pharmacokinetics and cardiovascular, sympatholytic, and sedative effects of SC and intravenously (IV) administered dexmedetomidine in healthy volunteers.

METHODS

An open two-period, cross-over design with balanced randomization was used. Ten male subjects were randomized to receive 1 μg/kg dexmedetomidine both IV and SC. Concentrations of dexmedetomidine and catecholamines in plasma were measured. Pharmacokinetic variables were calculated with non-compartmental methods. In addition, cardiovascular and sedative drug effects were monitored.

RESULTS

Eight subjects completed both treatment periods. Peak concentrations of dexmedetomidine were observed 15 min after SC administration (median; range 15-240). The mean bioavailability of SC dexmedetomidine was 81% (AUC_0-∞ ratio × 100%, range 49-97%). The mean (SD) peak concentration of dexmedetomidine in plasma was 0.3 (0.1) ng/ml, and plasma concentrations associated with sedative effects (i.e., > 0.2 ng/ml) were maintained for 4 h after SC dosing. Plasma noradrenaline concentrations were significantly lower (P < 0.001) within 3 h after IV than after SC administration. Subjective scores for vigilance and performance were significantly lower 0-60 min after IV than SC dosing (P < 0.001 for both). The onset of the cardiovascular, sympatholytic, and sedative effects of dexmedetomidine was clearly less abrupt after SC than IV administration.

CONCLUSIONS

Dexmedetomidine is relatively rapidly and efficiently absorbed after SC administration. Subcutaneous dexmedetomidine may be a feasible alternative in palliative sedation, and causes attenuated cardiovascular effects compared to IV administration. CLINICALTRIALS.

GOV IDENTIFIER

NCT02724098 . EUDRA CT number 2015-004698-34 .

Editor’s Choice- Sedation in the coronary intensive care unit: An adapted algorithm for critically ill cardiovascular patient

In the current era, cardiovascular intensive care units care for more complex patients who are far sicker than historical post-myocardial infarction patients, and sedation has become a common intervention in these units. Current sedation best practices derive mainly from non-cardiac units which limits their generalization to the critically ill cardiac patient. Thus, a great variability in sedation protocols, especially the selection of sedative agents, is commonly seen in daily practice across cardiac units. We present an updated review on sedation in cardiovascular critical care medicine with emphasis on the hemodynamic impact. The goal of this review is to generate a general sedation algorithm specific for the cardiac patient.

The Analgesic Effect of Ropivacaine Combined With Dexmedetomidine for Incision Infiltration After Laparoscopic Cholecystectomy

BACKGROUND

Local anesthetics infiltration is one consensus efficient strategy for pain relief after laparoscopic cholecystectomy (LC). The aim of this study was to investigate analgesia efficacy of incisional infiltration with ropivacaine plus dexmedetomidine.

METHODS

Patients scheduled for LC were assigned to 4 groups by different medications for trocar wound infiltration. The incidence of adverse events and the analgesic effect of ropivacaine combined with dexmedetomidine for incision infiltration were recorded.

RESULTS

Incisional infiltration of ropivacaine combining with dexmedetomidine could significantly reduce postoperative pain and the amount of pethidine requirement. Furthermore, it could also reduce time to walk without assistance, improve the efficacy of analgesia and sleep quality during the first night after LC, but did not increase the incidence of surgical adverse events.

CONCLUSIONS

The use of ropivacaine and dexmedetomidine may be considered as an alternative treatment for postoperative pain in patients undergoing LC.

Sedation with Dexmedetomidine or Propofol Impairs Hypoxic Control of Breathing in Healthy Male Volunteers

Background

In contrast to general anesthetics such as propofol, dexmedetomidine when used for sedation has been put forward as a drug with minimal effects on respiration. To obtain a more comprehensive understanding of the regulation of breathing during sedation with dexmedetomidine, the authors compared ventilatory responses to hypoxia and hypercapnia during sedation with dexmedetomidine and propofol.

Methods

Eleven healthy male volunteers entered this randomized crossover study. Sedation was administered as an intravenous bolus followed by an infusion and monitored by Observer’s Assessment of Alertness/Sedation (OAA/S) scale, Richmond Agitation Sedation Scale, and Bispectral Index Score. Hypoxic and hypercapnic ventilatory responses were measured at rest, during sedation (OAA/S 2 to 4), and after recovery. Drug exposure was verified with concentration analysis in plasma.

Results

Ten subjects completed the study. The OAA/S at the sedation goal was 3 (3 to 4) (median [minimum to maximum]) for both drugs. Bispectral Index Score was 82 ± 8 and 75 ± 3, and the drug concentrations in plasma at the sedation target were 0.66 ± 0.14 ng/ml and 1.26 ± 0.36 μg/ml for dexmedetomidine and propofol, respectively. Compared with baseline, sedation reduced hypoxic ventilation to 59 and 53% and the hypercapnic ventilation to 82 and 86% for dexmedetomidine and propofol, respectively. In addition, some volunteers displayed upper airway obstruction and episodes of apnea during sedation.

Conclusions

Dexmedetomidine-induced sedation reduces ventilatory responses to hypoxia and hypercapnia to a similar extent as sedation with propofol. This finding implies that sedation with dexmedetomidine interacts with both peripheral and central control of breathing.

Pharmacokinetics and pharmacodynamics of dexmedetomidine

Dexmedetomidine is an alpha-2 adrenoceptor agonist and has been used as a general anesthetic, sedative and analgesic for about 30 years. The aim of this paper is to review the pharmacokinetics and pharmacodynamics of dexmedetomidine, evaluate physiological factors that may affect the pharmacokinetics of dexmedetomidine, and summarize the pharmacodynamics of dexmedetomidine at different plasma levels. The pharmacokinetic parameters reported in previous studies according to noncompartmental analyses or population modeling results are compared. We concluded that the pharmacokinetic profile can be adequately described by a two-compartment model in population pharmacokinetic modeling. Body weight, height, albumin level, cardiac output, disease condition and other factors were considered to have significant influence on the clearance and/or distribution volume in different population pharmacokinetic models. The pharmacological effects of dexmedetomidine, such as sedation, heart rate reduction and biphasic change of blood pressure, vary at different plasma levels. These findings provide a reference for individualizing the dose of dexmedetomidine and achieving the desired pharmacological effects in clinical applications.

Low-dose intramuscular dexmedetomidine as premedication: a randomized controlled trial

BACKGROUND

Dexmedetomidine-induced bradycardia or hypotension has recently attracted considerable attention because of potentially grave consequences, including sinus arrest and refractory cardiogenic shock. A route other than intravenous injection or a low dose may help minimize cardiovascular risks associated with dexmedetomidine. However, few studies have addressed the clinical effects of low-dose intramuscular dexmedetomidine as premedication.

MATERIAL AND METHODS

Forty American Society of Anesthesiologists physical status I adult patients undergoing suspension laryngoscopic surgery were randomized to receive intramuscular dexmedetomidine (1 µg·kg-1) or midazolam (0.02 mg·kg-1) 30 minutes prior to anaesthesia induction. The sedative, hemodynamic, and adjuvant anaesthetic effects of both premedications were assessed.

RESULTS

The levels of sedation (Observer's Assessment of Alertness/Sedation scales) and anxiety (visual analog score) at pre-induction, and the times to eye-opening and extubation, were not different between the groups. The heart rate response following tracheal intubation and extubation, and mean arterial pressure responses after extubation, were attenuated in the dexmedetomidine group compared to the midazolam group. No bradycardia or hypotension was noted in any patients. Propofol target concentrations at intubation and at start and completion of surgery were decreased in the dexmedetomidine group, whereas no difference in respective remifentanil levels was detected.

CONCLUSIONS

This study provides further evidence that dexmedetomidine premedication in low dose (1 μg·kg-1) by intramuscular route can induce preoperative sedation and adjuvant anaesthetic effects without clinically significant bradycardia or hypotension.

Dexmedetomidine decreases the requirement of ketamine and propofol during burns debridement and dressings

Background and Aims:

Dexmedetomidine (Dex), a highly selective α₂-adrenoreceptor agonist, is used for sedation management in various clinical settings and shows anaesthetic-sparing effect. Our aim was to study the effects of Dex on requirements of propofol, ketamine, and intraoperative haemodynamic variations during burns debridement and dressing changes, and compare its effectiveness and safety with combination of ketamine and propofol.

Methods:

Sixty adult patients posted for elective debridement and dressing were included in the study. Thirty patients received Dex (intramuscular)(IM) 1 μg/kg, 1 h before shifting to the operation theatre while the other thirty did not. Anaesthesia was induced with propofol and ketamine followed by adjusted infusion to achieve a Ramsay Sedation Scale score (RSS) of six in all patients. Intraoperatively haemodynamic parameters were recorded at regular intervals of 5, 15, 30, 45, and 60 min. The mean data between the groups were compared by unpaired t test and medians by Mann-Whitney U test. Within group analysis was performed by using repeated measures ANOVA. P < 0.05 was considered significant.

Results:

The dose requirement of ketamine and propofol in Dex group was significantly lower when compared to control group (100.5 ± 17.58 mg vs. 231.5 ± 60.39 mg (P < 0.0001) and 127.7 ± 15.47 mg vs. 254 ± 59.22 mg (P < 0.0001) respectively). Additionally, recovery time was lower in the Dex group as compared to the control group, 9.57 ± 1.50 min vs. 11.53 ± 2.56 min (P = 0.0006). Haemodynamic variations were also significantly lower in the Dex group as compared to the control group.

Conclusion:

Dexmedetomidine (1 μg/kg IM) reduced the requirement of propofol and ketamine, with more stable intraoperative haemodynamics.

Dexmedetomidine for monitored anesthesia care in patients undergoing liberation procedure for multiple sclerosis: An observational study

Background:

It has been postulated that Multiple sclerosis (MS) stems from a narrowing in the veins that drain blood from the brain, known medically as chronic cerebrospinal venous insufficiency, or CCSVI. It has been proposed that balloon angioplasty should alleviate the symptoms of MS. This procedure is also known as The “Liberation Procedure”. Accordingly, a clinical study was undertaken to determine the effects of dexmedetomidine in patients undergoing the liberation procedure.

Aims:

To assess the effectiveness of dexmedetomidine in providing adequate sedation and pain relief for patients undergoing the liberation procedure.

Settings and design:

A prospective, nonrandomized observational study of 60 consecutive adult patients undergoing the liberation procedure under monitored anesthesia care (MAC) who will receive dexmedetomidine as an anesthetic agent.

Methods:

A total of 60 adult patients were enrolled in the study. Dexmedetomidine was administered to all patients in a loading dose of 1 mcg/kg, which was followed by a maintenance dose of 0.2–0.5 mcg/kg/h. The evaluation of quality of sedation was based on Ramsay Sedation and the quality of analgesia was assessed using the visual analog scale. The following parameters were measured continuously: heart rate, mean arterial pressure and hemoglobin oxygen saturation. Patients were asked to answer the question, “How would you rate your experience with the sedation you have received during surgery?” using a seven-point Likert-like verbal rating scale.

Statistical analysis:

Repeated measurements were analyzed by repeated measures ANOVA for HR and BP.

Results:

Most of our patients were satisfied with their sedation. In most of the patients, MAP and HR dropped after the bolus dose of dexmedetomidine, and the drop was statistically significant.

Conclusions:

Dexmedetomidine can be used as a sole sedative agent in patients undergoing the liberation procedure.

Intranasal atomized dexmedetomidine for sedation during third molar extraction

The purpose of this study was to evaluate the intranasal use of 1.5 μg/kg atomized dexmedetomidine for sedation in patients undergoing mandibular third molar removal. Eighteen patients underwent third molar removal in two surgical sessions. Patients were randomly assigned to receive intranasal water (placebo group) or 1.5 μg/kg atomized dexmedetomidine (group D) at the first session. The alternate regimen was used during the second session. Local anaesthesia was injected 30 min after placebo/sedative administration. Pain from local anaesthesia infiltration was rated on a scale from zero (no pain) to 10 (worst pain imaginable). Sedation status was measured every 10 min by a blinded observer with a modified Observer's Assessment of Alertness/Sedation (OAA/S) scale and the bispectral index (BIS). Adverse reactions and analgesic consumption were recorded. Sedation values in group D were significantly different from placebo at 20-30 min, peaked at 40-50 min, and returned to placebo levels at 70-80 min after intranasal drug administration. Group D displayed decreased heart rate and systolic blood pressure, but the decreases did not exceed 20% of the baseline values. Intranasal administration of 1.5 μg/kg atomized dexmedetomidine is effective, convenient, and safe as a sedative for patients undergoing third molar extraction.

Intramuscular dexmedetomidine: an effective route of sedation preserves background activity for pediatric electroencephalograms

OBJECTIVES

To describe the efficacy and outcome of dexmedetomidine (Dex) via the intramuscular (IM) route for sedation for electroencephalography (EEG).

STUDY DESIGN

Quality assurance data and EEG studies were reviewed for consecutive patients who received IM Dex for EEGs between August 2007 and September 2009. Sleep spindles, delta waves, and beta activity were evaluated to determine the deepest stage of sleep achieved.

RESULTS

One hundred seven consecutive children (age 0.2-17 years) between August 2007 and September 2009 received IM Dex (range 1.0-4.5 mcg/kg). The average time to achieve sedation was 15.5 minutes (range 3.0-55.0) with an average of 54.5 minutes to meet discharge criteria following EEG studies, which averaged 34.2 ± 22.6 minutes. The deepest stage of sleep recorded for each child was: awake (n = 1), stage N2 (n = 51), and stage N3 (n = 55). Excessive beta activity was seen in only 1 patient. Epileptiform activity was noted in 11 patients. Hemodynamic fluctuations in heart rate and blood pressure were noted, none of which required pharmacologic intervention. All EEGs were successfully completed.

CONCLUSION

We describe Stage 3 sleep and preserved background activity in response to Dex. We present the IM route as a new method, which preserves background EEG activity to provide safe and effective sedation for EEG studies.

The effect of site (deltoid or gluteus muscle) of intramuscular administration of anaesthetic drugs on the course of immobilisation in macaque monkeys (Macaca mulatta)

The aim of this work was to study the effect of site of intramuscular administration of anaesthetic drugs on the course of immobilisation in macaque monkeys (Macaca mulatta). Twenty macaque monkeys were given medetomidine (25 µg·kg-1) and ketamine (3 mg·kg-1) intramuscularly to the deltoid (n = 10 animals) or gluteus (n = 10 animals) muscles. Behavioural changes, loss of aggressiveness, immobilisation time and cardiorespiratory changes were recorded. The effect of drugs was reversed after 20 min by i.m. administration of atipamezole at the dose of 250 µg·kg-1. Highly significant differences (P < 0.001) were found between groups with gluteal or deltoid administration of drugs on the onset of immobilisation effect (71.3 s and 108.3 s, respectively), and immobilisation time (152.7 s and 254.4 s, respectively). In the gluteus muscle group, the grasp reflex was still present at the beginning of immobilisation and slowly wore off in 15–45 s. The same was valid for muscle tone. There were no differences in cardiorespiratory parameters in any of the groups. Animals of both groups recovered in 3–6 min after atipamezole administration. Administration of drugs to the deltoid muscle resulted in a more rapid onset and increased effect of immobilisation than administration to the gluteus muscle. Both in veterinary and human medicine, injection to the deltoid muscle may be more convenient in all cases, when rapid and more prominent effect is desirable as in premedication before surgery or in emergency medicine. The study is the first to compare the effect of administering drugs to different muscles and the results may improve the practice of intramuscular injections in animals and in humans.

Review Article: Dexmedetomidine: Does it Have Potential in Palliative Medicine?

Dexmedetomidine, is a α 2 adrenergic agonist approved by the Food and Drug administration for sedation and analgesia. A highly potent α2 adrenergic agonist, it has quick onset of action, with peak effects within 1 hour of administration. It is metabolized in the liver and eliminated in the urine as a glucuronide. Dexmedetomidine is a substrate and inhibitor of cytochrome oxidase 2D6, but clinical evidence of significant drug interactions is lacking. Clinical trials suggest efficacy for the treatment of delirium in the intensive care unit setting with efficacy comparable to haloperidol and benzodiazepines. Dexmedetomidine also has an opioid-sparing action and can act to enhance analgesia. The purpose of this article is to review the pharmacodynamics and pharmacology of dexmedetomidine, and examine its potential use in the palliative care population, especially with regard to the management of delirium.

Dexmedetomidine: clinical application as an adjunct for intravenous regional anesthesia

The selective α-2 adrenoceptor agonist, dexmedetomidine, has been shown to be a useful, safe adjunct in perioperative medicine. Intravenous regional anesthesia is one of the simplest forms of regional anesthesia and has a high degree of success. However, intravenous regional anesthesia is limited by the development of tourniquet pain and its inability to provide postoperative analgesia. To improve block quality, prolong postdeflation analgesia, and decrease tourniquet pain, various chemical additives have been combined with local anesthetics, although with limited success. The antinociceptive effects of α-2 adrenoceptor agonists have been shown in animals and in humans. However, less is known about the clinical effects of dexmedetomidine when coadministered with local anesthetics in patients undergoing intravenous regional anesthesia. This review examines what is currently known to improve our understanding of the properties and application of dexmedetomidine when used as an adjunct in intravenous regional anesthesia.

α2-Adrenergic agonists protect against radiocontrast-induced nephropathy in mice

Radiocontrast nephropathy (RCN) is a common clinical problem for which there is no effective therapy. Utilizing a murine model, we tested the hypothesis that α2-adrenergic receptor agonists (clonidine and dexmedetomidine) protect against RCN induced with iohexol (a nonionic low-osmolar radiocontrast). C57BL/6 mice were pretreated with saline, clonidine, or dexmedetomidine before induction of RCN. Some mice were pretreated with yohimbine (a selective α2-receptor antagonist) before saline, clonidine, or dexmedetomidine administration. α2-Agonist-treated mice had reduced plasma creatinine, renal tubular necrosis, renal apoptosis, and renal cortical proximal tubule vacuolization 24 h after iohexol injection. Yohimbine reversed the protective effects of clonidine and dexmedetomidine pretreatment. Injection of iohexol resulted in a rapid (∼90 min) fall of renal outer medullary blood flow. Clonidine and dexmedetomidine pretreatment significantly attenuated this perfusion decrease without changing systemic blood pressure. To determine whether proximal tubular α2-adrenergic receptors mediate the cytoprotective effects, we treated cultured human proximal tubule (HK-2) cells and rat pulmonary microvascular endothelial cells with iohexol after vehicle, clonidine, or dexmedetomidine pretreatment. Iohexol caused a direct dose-dependent reduction of HK-2 and rat pulmonary microvascular endothelial cell viability, but α2-agonists failed to preserve the viability of both cell types. We conclude that α2-adrenergic receptor agonists protect mice against RCN by preserving outer medullary renal blood flow. As α2-agonists are widely utilized during the perioperative period, our findings may have significant clinical relevance to improving outcomes following radiocontrast exposure.

A Double-Blind, Crossover Assessment of the Sedative and Analgesic Effects of Intranasal Dexmedetomidine

BACKGROUND

The alpha2-receptor agonist, dexmedetomidine, provides sedation with facilitated arousal and analgesia with no respiratory depression. These properties render it potentially useful for anesthesia premedication, although parenteral administration is not practical in this setting. We designed this study to evaluate the sedative, anxiolytic, analgesic, and hemodynamic effects of dexmedetomidine administered intranasally in healthy volunteers.

METHODS

Koch's design for crossover trials (three-treatment and two-period design) was adopted. The study was double-blind and there were three treatment groups: A (placebo), B (intranasal dexmedetomidine 1 microg/kg) and C (intranasal dexmedetomidine 1.5 microg/kg). Each of the 18 subjects participated in two study periods. The study drug was administered intranasally after baseline observations of modified Observer Assessment of Alertness/Sedation Scale, visual analog scale of sedation, bispectral index, visual analog scale of anxiety, pain pressure threshold measured by an electronic algometer, systolic blood pressure (SBP) and diastolic blood pressure, heart rate, respiratory rate, and oxygen saturation. These were repeated during the course of the study.

RESULTS

Intranasal dexmedetomidine was well tolerated. Both 1 and 1.5 microg/kg doses equally produced significant sedation and decreases in bispectral index, SBP, diastolic blood pressure, and heart rate when compared with placebo (P < 0.05). The onset of sedation occurred at 45 min with a peak effect at 90-150 min. The maximum reduction in SBP was 6%, 23%, and 21% for Groups A, B, and C respectively. There was no effect on pain pressure threshold, oxygen saturation or respiratory rate. Anxiolysis could not be evaluated as no subjects were anxious at baseline.

CONCLUSION

The intranasal route is effective, well tolerated, and convenient for the administration of dexmedetomidine. Future studies are required to evaluate the possible role of the noninvasive route of administration of dexmedetomidine in various clinical settings, including its role as premedication prior to induction of anesthesia.

Dexmedetomidine vs midazolam for monitored anaesthesia care during cataract surgery

BACKGROUND

Cataract surgery is commonly performed under local anaesthesia with midazolam sedation. Dexmedetomidine, a sedative-analgesic, is devoid of respiratory depressant effects, and its use in cataract surgery has not been reported. This double-blind study compared the use of dexmedetomidine and midazolam in patients undergoing cataract surgery.

METHODS

Forty-four patients undergoing cataract surgery under peribulbar anaesthesia randomly received either i.v. dexmedetomidine 1 microg kg(-1) over 10 min; followed by 0.1-0.7 microg kg(-1) h(-1) i.v. infusion (Group D), or midazolam 20 microg kg(-1) i.v.; followed by 0.5 mg i.v. boluses as required (Group M). Sedation was titrated to a Ramsay sedation score of 3. Mean arterial pressure (MAP), heart rate (HR), readiness for recovery room discharge (time to Aldrete score of 10), and patients' and surgeons' satisfaction (on a scale of 1-7) were determined.

RESULTS

MAP and HR were lower in Group D compared with Group M [86 (se 3) vs 102 (3) mm Hg and 65 (2) vs 72 (2) beats min(-1), respectively] (P<0.05). Group D patients had slightly higher satisfaction with sedation [median (IQR): 6 (6-7) vs 6 (5-7), P<0.05], but delayed readiness for discharge [45 (36-54) vs 21 (10-32) min, P<0.01] compared with patients in Group M. Surgeons' satisfaction was comparable in both groups [5 (4-6) vs 5 (4-6)].

CONCLUSION

Compared with midazolam, dexmedetomidine does not appear to be suitable for sedation in patients undergoing cataract surgery. While there was a slightly better subjective patient satisfaction, it was accompanied by relative cardiovascular depression and delayed recovery room discharge.

Dexmedetomidine sedation in a pediatric cardiac patient scheduled for mri

PURPOSE

To describe the use of dexmedetomidine for sedation in a critically ill infant undergoing magnetic resonance imaging (MRI).

CLINICAL FEATURES

A nine-month-old 5.1 kg infant was to have an MRI study of the thorax. The infant had multiple congenital cardiac anomalies which had been partially corrected surgically. After administration of atropine, 0.1 mg iv, a loading dose of dexmedetomidine (1 microg.kg(-1) iv) was administered over ten minutes followed by a continuous infusion of 0.5 microg.kg(-1).hr(-1) for maintenance. Propofol 5 mg iv were administered after the loading dose of dexemedetomidine to produce somnolence. Anesthetic conditions for performing the MRI were excellent. The infant remained motionless, breathing spontaneously. Hemodynamics remained stable throughout the procedure. Recovery was rapid and uneventful.

CONCLUSION

Dexmedetomidine and a small dose of propofol were used successfully to sedate a critically ill infant for MRI. More studies are required to determine the role of this unique drug in the pediatric population.

Comparative tolerability of sedative agents in head-injured adults

Sedative agents are widely used in the management of patients with head injury. These drugs can facilitate assisted ventilation and may provide useful reductions in cerebral oxygen demand. However, they may compromise cerebral oxygen delivery via their cardiovascular effects. In addition, individual sedative agents have specific and sometimes serious adverse effects. This review focuses on the different classes of sedative agents used in head injury, with a discussion of their role in the context of clinical pathophysiology. While there is no sedative that has all the desirable characteristics for an agent in this clinical setting, careful titration of dose, combination of agents, and a clear understanding of the pathophysiology and pharmacology of these agents will allow safe sedative administration in head injury.

Bioavailability of dexmedetomidine after extravascular doses in healthy subjects

AIM

To determine the absolute bioavailability of extravascularly administered dexmedetomidine, a novel a2-adrenoceptor agonist, in healthy subjects.

METHODS

Single 2 microg x kg-1 doses of dexmedetomidine were given intravenously, intramuscularly, perorally and buccally (where the solution is not swallowed) to 12 healthy male subjects. The drug concentration-time data were analysed using linear one-compartment (buccal and peroral data), or two-compartment modelling (intravenous data), or noncompartmental methods (intramuscular data).

RESULTS

Mean (95% CI) absolute bioavailability after peroral, buccal and intramuscular administration was 16% (12-20%), 82% (73-92%) and 104% (96-112%), respectively.

CONCLUSION

Dexmedetomidine is well absorbed systemically through the oral mucosa, and therefore buccal dosing may provide an effective, noninvasive route to administer the drug.

The pharmacokinetics of dexmedetomidine in volunteers with severe renal impairment

Dexmedetomidine, an alpha2-adrenergic agonist with sedative and analgesic properties, is mainly cleared by hepatic metabolism. Because the pharmacokinetics of dexmedetomidine have not been determined in humans with impaired renal function, we studied them in volunteers with severe renal disease and in control volunteers. Six volunteers with severe renal disease and six matched volunteers with normal renal function received dexmedetomidine, 0.6 microg/kg, over 10 min. Venous blood samples for the measurement of plasma dexmedetomidine concentrations were drawn before, during, and up to 12 h after the infusion. Two-compartmental pharmacokinetic models were fit to the drug concentration versus time data. We also determined its hemodynamic, respiratory, and sedative effects. There was no difference between Renal Disease and Control groups in either volume of distribution at steady state (1.81 +/- 0.55 and 1.54 +/- 0.08 L/kg, respectively; mean +/- SD) or elimination clearance (12.5 +/- 4.6 and 8.9 +/- 0.7 mL x min(-1) x kg(-1), respectively). However, elimination half-life was shortened in the Renal Disease group (113.4 +/- 11.3 vs 136.5 +/- 13.0 min; P < 0.05). A mild reduction in blood pressure occurred in most volunteers. Although most volunteers were sedated by dexmedetomidine, renal disease volunteers were sedated for a longer period of time.

IMPLICATIONS

The pharmacokinetics of dexmedetomidine in volunteers with severe renal impairment differed little from those in volunteers with normal renal function. In addition, there were no clinically significant differences in the hemodynamic responses to dexmedetomidine. However, dexmedetomidine resulted in more prolonged sedation in subjects with renal disease.

Receptor subtype and dose dependence of dexmedetomidine-induced accumulation of [14C]glutamine in astrocytes suggests glial involvement in its hypnotic-sedative and anesthetic-sparing effects

Dexmedetomidine, a selective alpha(2)-adrenergic agonist, increases accumulation of [14C]glutamine and its labeled metabolites in primary cultures of mouse astrocytes. The concentration dependence is biphasic and identical to that previously described for dexmedetomidine's effect on free cytosolic calcium concentration ([Ca(2+)](i)) in astrocytes, and both effects are exerted on the alpha(2A) subtype of the alpha(2) receptor, suggesting a Ca(2+)-mediated effect. The concentration corresponding to the most potent effect is similar to that with which dexmedetomidine exerts its anesthetic-sparing activity in vivo, and the second peak corresponds to its hypnotic-sedative effect. It is suggested that both effects may be caused by decreased glutamatergic neurotransmission, secondary to reduced availability of glutamine as a glutamate precursor in glutamatergic neurons.

Dexmedetomidine-induced stimulation of glutamine oxidation in astrocytes: a possible mechanism for its neuroprotective activity

Dexmedetomidine is a highly specific alpha2-adrenergic agonist, which is used clinically as an anesthetic adjuvant and in animal experiments has a neuroprotective effect during ischemia. The current study showed that dexmedetomidine enhances glutamine disposal by oxidative metabolism in astrocytes. This effect occurs at pharmacologically relevant concentrations. It is exerted on alpha2-adrenergic receptors and not on imidazoline-preferring sites, and it is large enough to reduce the availability of glutamine as a precursor of neurotoxic glutamate.

Method for comparison of the hemodynamic effects of equi-antinociceptive oral doses of drugs in anesthetized rats

In a typical flowchart for discovery of novel analgesic (or other) agents, a critical path often involves maximization of the separation of the therapeutic endpoint from known adverse-effect (AE) endpoint(s). Although strategies can easily be designed for in vitro paradigms such as high-throughput screening, extension to in vivo testing can represent a major obstacle to the rapid progression to the next step in development. The problem can be particularly acute when the assessment is required for oral dosing, and when it is not known if the therapeutic and AE mechanism(s) of action are the same. As a case in point, alpha(2)-adrenoceptor (alpha(2)-AR) agonists have potential therapeutic use as analgesics, but they also produce cardiovascular (CV) effects. However, whether the two effects are inexorably linked has not been resolved, particularly for oral administration. The present study used a novel method for comparing the CV effects produced by alpha(2)-AR agonists given by intraduodenal administration to anesthetized rats at fixed ratios of the oral antinociceptive ED(50) dose of each agonist. The technique provided a useful screen of compounds. In addition,there was no correlation between CV endpoints and alpha(2A)-AR affinity, suggesting that oral alpha(2)-AR-mediated analgesia and CV effects might be separable or that other mechanisms might be involved.

Comparison of three doses of dexmedetomidine with medetomidine in cats following intramuscular administration

Cats (n = 6) were administered dexmedetomidine (DEX) and medetomidine (MED) at three different dose levels in a randomized, blinded, cross-over study. DEX was administered at 25, 50 and 75 microg/kg (D25, D50 and D75), corresponding to MED 50, 100 and 150 microg/kg (M50, M100 and M150). Sedation, analgesia and muscular relaxation were scored subjectively. Heart and respiratory rates and rectal temperature were measured. Corresponding doses of DEX and MED were compared. Effects were also compared between dose levels for each compound. At dose level 2 (D50-M100), the duration of effective clinical sedation was significantly shorter after DEX (202.5 +/- 16.0 min) than after MED (230.0 +/- 41.2 min). Proceeding from D50-M100 to D75-M150, the duration of effective clinical sedation was increased more after DEX (by 57.5 +/- 38.4 min) than after MED (by 14.2 +/- 41.9 min) Increasing from D50-M100 to D75-M150, heart rate was further decreased after DEX (by 8.1 +/- 13.4%) but not after MED. There was no statistically significant difference between corresponding doses of DEX and MED for any of the other parameters studied. Changes in sedation, analgesia and muscular relaxation were dose-dependent. It was concluded that anaesthetic effects of medetomidine in cats are probably due entirely to its d-isomer and that dexmedetomidine at 25, 50 and 75 microg/kg induces dose-dependent sedation, analgesia and muscular relaxation of clinical significance in cats.

Dexmedetomidine alleviates ethanol withdrawal symptoms in the rat

The effect of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, on ethanol withdrawal symptoms was studied in chronically ethanol-fed rats. After a 4-day ethanol intoxication period the rats were given s.c. injections of dexmedetomidine (3, 10, or 30 micrograms/kg) or saline (control group) at 10, 16, 22, and 39 h after the last dose of ethanol. The severity of ethanol withdrawal symptoms (rigidity, tremor, irritability, hypoactivity) was rated up to 58 h, blind to the treatments. The results showed that dexmedetomidine at doses 10 and 30 micrograms/kg significantly diminished the severity of the ethanol withdrawal reaction as measured by the sum score of the three most specific withdrawal signs (rigidity, tremor, and irritability). Dexmedetomidine at 10 micrograms/kg was the most effective dose, especially in the latter half of the withdrawal period (23-58 h after last dose of ethanol). The results suggest that dexmedetomidine in the treatment of ethanol withdrawal symptoms should be further studied.

Single dose pharmacokinetics of medetomidine in sheep

The pharmacokinetics of medetomidine hydrochloride (Domitor) administered at a single dose of 15 micrograms/kg i.v. in sheep are described. Plasma medetomidine concentrations were determined using a sensitive radioreceptor assay technique, capable of also measuring metabolites which would bind to alpha 2 adrenergic receptors. Medetomidine was rapidly distributed, with a half-life of distribution of 4.65 +/- 0.65 min. The apparent volume of distribution was 2.69 +/- 0.62 L/kg, while elimination half-life was 37.85 +/- 2.84 min. Total body clearance varied between 16.29 and 151.81 mL/min.kg. Pharmacological effects of medetomidine paralleled its plasma concentration.

Systemic absorption and systemic effects of ocularly administered dexmedetomidine in rabbits

Dexmedetomidine is a selective alpha 2-adrenoceptor agonist which has previously been shown to reduce the ocular pressure of normotensive rabbits as well as those with pressures artificially elevated by laser irradiation. In this study instillation of an equivalent hypotensive dose (12.5 micrograms) did not cause changes in heart rate, blood pressure, blood glucose or plasma catecholamine content even though dexmedetomidine could be detected in plasma. However, this dose given intravenously (i.v.) was also without effect. Higher ocular doses resulted in equivalent bradycardia and changes in blood glucose levels as when the dose was given i.v. These two parameters proved to be most sensitive indicators of systemic alpha 2-agonism, blood pressure did not change and plasma catecholamine levels were too low to be reliably assayed. It is concluded that when hypotensive doses of dexmedetomidine are instilled into the eye, intraocular concentrations are sufficiently high to exert pharmacological effects. As it is absorbed into the general circulation, it is diluted such that its systemic effects are minimal.