Dexmedetomidine: Clinical update

Dexmedetomidine Improves Cardiovascular and Ventilatory Outcomes in Critically Ill Patients: Basic and Clinical Approaches

Dexmedetomidine (DEX) is a highly selective α2-adrenergic agonist with sedative and analgesic properties, with minimal respiratory effects. It is used as a sedative in the intensive care unit and the operating room. The opioid-sparing effect and the absence of respiratory effects make dexmedetomidine an attractive adjuvant drug for anesthesia in obese patients who are at an increased risk for postoperative respiratory complications. The pharmacodynamic effects on the cardiovascular system are known; however the mechanisms that induce cardioprotection are still under study. Regarding the pharmacokinetics properties, this drug is extensively metabolized in the liver by the uridine diphosphate glucuronosyltransferases. It has a relatively high hepatic extraction ratio, and therefore, its metabolism is dependent on liver blood flow. This review shows, from a basic clinical approach, the evidence supporting the use of dexmedetomidine in different settings, from its use in animal models of ischemia-reperfusion, and cardioprotective signaling pathways. In addition, pharmacokinetics and pharmacodynamics studies in obese subjects and the management of patients subjected to mechanical ventilation are described. Moreover, the clinical efficacy of delirium incidence in patients with indication of non-invasive ventilation is shown. Finally, the available evidence from DEX is described by a group of Chilean pharmacologists and clinicians who have worked for more than 10 years on DEX.

The Effects of Dexmedetomidine Administration on Postoperative Blood Glucose Levels in Diabetes Mellitus Patients Undergoing Spinal Anesthesia: A Pilot Study

Background

Dexmedetomidine (DEX) is an α2-adrenergic receptor agonist with sedative and sympatholytic effects. It inhibits the stress response and insulin secretion. Therefore, postoperative changes to blood glucose levels were investigated when DEX was intraoperatively infused for sedation purposes in diabetic patients under spinal anesthesia.

Methods

Twenty diabetic patients were randomly allocated to two groups (n = 10). Group A patients were infused with DEX at a dose of 0.4 - 0.8 μg/kg/hour and group B (control) patients were infused with the same volume of normal saline. The blood glucose levels were measured preoperatively and at 1, 3, 6, 12, and 24 hours postoperatively.

Results

There was no statistically significant difference between the blood glucose levels in groups A and B up to 24 hours postoperatively (P = 0.088). A statistically significant difference in the blood glucose level was not demonstrated 24 hours after surgery in comparison with the baseline level in Group A. The blood glucose level significantly decreased at three hours in group B in comparison with the level at baseline (P = 0.007) and increased at 24 hours (P = 0.037).

Conclusions

An intraoperative DEX infusion maintains blood glucose levels at a constant level relative to baseline in diabetic patients within 24 hours postoperatively. The frequency of hyperglycemia was low in group A in the perioperative period compared with that in the control group (group B).

Ketamine alone or combined with midazolam or dexmedetomidine does not affect anxiety-like behaviours and memory in adult Wistar rats

Ketamine administration has been associated with controversial behavioural impairments and psychotic episodes. Even though ketamine alone and in combination with midazolam or dexmedetomidine are frequently used in laboratory animals, the side-effects of such protocols are not well known. Therefore, our aim was to evaluate the effects of ketamine alone and in combination with midazolam or dexmedetomidine on emotional reactivity, as well as the effects on learning and memory in adult rats at least 48 h after anaesthesia. The evaluation of the potential influence of 100 mg/kg ketamine administered alone and in combination with midazolam (5 mg/kg), or dexmedetomidine (0.25 mg/kg) on spatial learning and recognition memory was studied in adult Wistar rats using the radial maze as well as object recognition and location tests. The influence of these combinations on emotional reactivity was investigated using the new exploration test and the elevated plus maze. Results showed that ketamine alone or in combination with midazolam or dexmedetomidine affected neither spatial and recognition memory, nor emotional reactivity. These results reinforce the safe clinical use of ketamine and its combinations in rats in a research context since the administration of these anaesthetic combinations did not produce significant changes with regard to spatial and recognition memory or emotional reactivity. Furthermore, these results indicate that the quality of scientific data produced in adult rat neurobehavioural research is not jeopardized by the use of these anaesthetic protocols.

Comparison of Effects of Different Dexmedetomidine and Chloral Hydrate Doses Used in Sedation on Electroencephalography in Pediatric Patients

The aim of this study was to compare the efficacy and safety of different oral chloral hydrate and dexmedetomidine doses used for sedation during electroencephalography (EEG) in children. One hundred sixty children aged 1 to 9 years with American Society of Anesthesiologists physical status I-II who were uncooperative during EEG recording or who were referred to our electrodiagnostic unit for sleep EEG were included to the study. The patients were randomly assigned into 4 groups. In groups D1 and D2, patients received oral dexmedetomidine doses of 2 and 3 µg/kg, respectively. In group C1 and C2, patients received oral chloral hydrate doses of 50 and 100 mg/kg, respectively. The induction time was significantly shorter in group C2 compared with other groups (P = .000). The rate of adverse effects was significantly higher in group C2 compared with the dexmedetomidine groups (D1 and D2; P = .004). In conclusion, dexmedetomidine can be used safely for sedation during EEG in children.

The effectiveness of intramuscular dexmedetomidine on hemodynamic responses during tracheal intubation and anesthesia induction of hypertensive patients: a randomized, double-blind, placebo-controlled study

BACKGROUND

Hypertensive patients are at risk for increased hemodynamic response to tracheal intubation. Sympatholytic drugs administered during the preinduction period may prevent adverse events.

OBJECTIVE

We assessed the effectiveness of a single preinduction IM bolus dose of dexmedetomidine (DMED) 2.5 μg/kg in attenuating hemodynamic responses to tracheal intubation and rapid-sequence anesthesia induction in hypertensive patients treated with angiotensin-converting enzyme inhibitors.

METHODS

Adult patients (American Society of Anesthesiologists classification II and III) with essential hypertension, scheduled for elective abdominal or gynecologic surgery, were enrolled in this randomized, double-blind, placebo-controlled study. Patients were assigned to i of 2 groups: the DMED group received IM DMED 2.5 μg/kg and the placebo group received IM saline 0.9% 45 to 60 minutes before induction of anesthesia. General anesthesia was induced with thiopental, fentanyl, and vecuronium and maintained with a sevoflurane-nitrous oxide-oxygen mixture. Hemodynamic values were recorded before (baseline) and after anesthesia induction, before endotracheal intubation, and 1, 3, and 5 minutes after intubation. The patients were monitored for hypotension (systolic arterial pressure [SAP] decreased ≥25% from baseline or to <90 mm Hg) or bradycardia (heart rate [HR] decreased ≥25% from baseline or to <50 beats/min).

RESULTS

Nine hundred sixty patients were assessed for enrollment during a 6-month period. Sixty patients (49 women, 11 men; mean [SD] age, 59.16 [8.39] years) were eligible for the study. There were no significant differences in baseline hemodynamic values between the groups. SAP and diastolic arterial pressure (DAP) before anesthesia induction, 1 and 3 minutes after intubation, and DAP 1 minute after intubation were significantly lower in the DMED group than in the placebo group (all, P < 0.05). There were no significant between-group differences in SAP or DAP 5 minutes after intubation. HR before anesthesia induction, before intubation, and 1, 3, and 5 minutes after intubation were lower in the DMED group than in the control group (all, P < 0.05). In the DMED group, SAP after intubation, DAP before intubation, 3 and 5 minutes after intubation, HR before induction, before intubation, and 3 and 5 minutes after intubation were significantly decreased compared with baseline values (all, P < 0.05). In the control group, SAP at all times, DAP before intubation, 1, 3, and 5 minutes after intubation, HR before intubation, and 3 and 5 minutes after intubation were significantly decreased compared with baseline values (all, P < 0.05). Hypotension and bradycardia were observed together in 3 patients, and hypotension alone was observed in 1 patient 3 minutes after intubation in the DMED group; hypotension was observed in 1 patient at 3 minutes after intubation in the control group.

CONCLUSION

The results of this study suggest that IM DMED 2.5 μg/kg administered 45 to 60 minutes before anesthesia induction attenuated, but did not completely prevent, hemodynamic responses to tracheal intubation in these patients with essential hypertension.

Dexmedetomidine pharmacokinetics in pediatric intensive care--a pooled analysis

BACKGROUND

Published dexmedetomidine pharmacokinetic studies in children are limited by participant numbers and restricted pathology. Pooling the available studies allows investigation of covariate effects.

METHODS

Data from four studies investigating dexmedetomidine pharmacokinetics after i.v. administration (n = 95) were combined to undertake a population pharmacokinetic analysis of dexmedetomidine time-concentration profiles (730 observations) using nonlinear mixed effects modeling (NONMEM). Estimates were standardized to a 70-kg adult using allometric size models.

RESULTS

Children had a mean age of 3.8 (median 3 years, range 1 week-14 years) and weight of 16.0 kg (median 13.3 kg, range 3.1-58.9 kg). Population parameter estimates (between subject variability) for a two-compartment model were clearance (CL) 42.1 (CV 30.9%) lx h(-1) x 70 kg(-1), central volume of distribution (V1) 56.3 (61.3%) l.70 kg(-1), inter-compartment clearance (Q) 78.3 (37.0%) l x h(-1) x 70 kg(-1) and peripheral volume of distribution (V2) 69.0 (47.0%) l.70 kg(-1). Clearance maturation with age was described using the Hill equation. Clearance increases from 18.2 l x h(-1) x 70 kg(-1) at birth in a term neonate to reach 84.5% of the mature value by 1 year of age. Children given infusion after cardiac surgery had 27% reduced clearance compared to a population given bolus dose. Simulation of published infusion rates that provide adequate sedation for intensive care patients found a target therapeutic concentration of between 0.4 and 0.8 microg x l(-1).

CONCLUSIONS

The sedation target concentration is similar to that described for adults. Immature clearance in the first year of life and a higher clearance (when expressed as l x h(-1) x kg(-1)) in small children dictate infusion rates that change with age. Extrapolation of dose from children given infusion in intensive care after cardiac surgery may not be applicable to those sedated for noninvasive procedures out of intensive care.

Hypoglycemia associated with dexmedetomidine overdose in a child?

The case of an asymptomatic 20 month-old, 10.7-kg girl, scheduled for interventional cardiac catheterization to close a patent ductus arteriosus, who suffered significant hypoglycemia possibly related in part to an overdose of dexmedetomidine, is reported. An infusion of dexmedetomidine was started using a programmable syringe pump at the intended administration rate of one mcg/kg/hr, but was actually incorrectly programmed at the rate of one mcg/kg/min. The infusion continued for 36 minutes until a total of 380 mcg (36 mcg/kg) had been given, and was stopped when the error was discovered. A peripheral blood sugar level was found to be 26 mg/dL. The significant hypoglycemia likely was due to substrate deficiency, with a possible dexmedetomidine effect.

Dexmedetomidine disposition in children: a population analysis

BACKGROUND

There are few data describing dexmedetomidine population pharmacokinetics (PK) in children (0-15 years) despite increasing use.

METHODS

An open-label study was undertaken to examine the PK of i.v. dexmedetomidine 1-4 mug.kg(-1) bolus in children after cardiac surgery (n = 45). A population PK analysis of dexmedetomidine time-concentration profiles (148 observations) was undertaken using nonlinear mixed effects modeling. Estimates were standardized to a 70-kg adult using allometric size models.

RESULTS

Children had a mean age of 3.38 years (range 4 days to 14 years) and weight 15.1 kg (range 3.1-58.9 kg). A two-compartment disposition model with first order elimination was superior to a one-compartment model. Population parameter estimates (between subject variability) were clearance (CL) 39.2 (CV 30.36%) l.h(-1) per 70 kg, central volume of distribution (V1) 36.9 (69.49%) l per 70 kg, inter-compartment clearance (Q) 68.2 (37.6%) l.h(-1) per 70 kg and peripheral volume of distribution (V2) 69.9 (48.6%) l per 70 kg. Clearance at birth was 15.55 l.h(-1) per 70 kg and matured with a half-time of 46.5 weeks to reach 87% adult rate by 1 year of age. Simulation of an infusion of 1 mug.kg(-1) over 10 min followed by an infusion of 0.7 mug.kg(-1).h(-1) for 50 min suggested that children arouse from sedation at a plasma concentration of 0.304 mug.l(-1).

CONCLUSIONS

Clearance in neonates is approximately one-third of that described in adults, consistent with immature elimination pathways. Maintenance dosing, which is a function of clearance, should be reduced in neonates and infants when using a target concentration approach.

Undiagnosed catecholamine-secreting paraganglioma and coexisting carcinoid in a patient with MH susceptibility: an unusual anesthetic challenge

The management of a patient with two undiagnosed neuroendocrine tumors and possible malignant hyperthermia (MH) susceptibility poses a unique challenge to the anesthesiologist. We describe a total intravenous anesthetic including an alpha 2-agonist infusion combined with epidurally administered bupivacaine for intra- and postoperative pain management. Alpha 2-agonists may offer improved intraoperative hemodynamic management in patients with catecholamine-secreting tumors and reduce the total dose needed for intravenous anesthetics such as propofol. The latter mechanism may be useful to avert the risk of the propofol infusion syndrome occurring as a consequence of a high cumulative dose following its prolonged administration.

Comparing Dexmedetomidine Prescribing Patterns and Safety in the Naturalistic Setting Versus Published Data

BACKGROUND:

In clinical practice, new drugs may be used differently than the product labeling recommends. Furthermore, it often takes several years of use before adverse drug reactions (ADRs) are reported.

OBJECTIVE:

To compare prescribing patterns and safety of the newly released drug dexmedetomidine as observed in clinical practice with published data on the drug.

METHODS:

Information from a convenience sample of adults receiving dexmedetomidine as part of routine patient care at 10 institutions was retrospectively collected from June 27, 2001, to May 31, 2002. Investigators reviewed medical records daily and entered dosing information, patient demographics, and predefined categories of ADR severity and probability anonymously via the Internet on a secure server.

RESULTS:

Only 33% of the total sample (n = 136) of patients received a loading infusion of dexmedetomidine; however, maintenance dosing was usually within product labeling guidelines. Of note, 27.2% of patients received dexmedetomidine above the maximum dose and 33.8% received the drug beyond 24 hours. Some patients (15.4%) were never mechanically ventilated, while 59.5% received dexmedetomidine following extubation for an average of 11.3 hours. ADRs were reported in 30% of patients: 20% of the reactions required treatment or increased length of stay. Hypotension was the most common ADR, occurring in 22.7% of patients. Bradycardia was reported in 4.4% of patients. The rate and type of ADRs were similar in patients receiving dexmedetomidine >24 hours compared with the total population.

CONCLUSIONS:

Dexmedetomidine is prescribed within product labeling guidelines except for low use of a loading dose, some patients received the drug at doses above the maximum, and others received it for longer than 24 hours. Since ADR rates are similar to those of other published reports, dexmedetomidine maintained its expected safety profile in our patients.

Dexmedetomidine Overdose in the Perioperative Setting

OBJECTIVE

To report 3 cases of accidental dexmedetomidine overdose in the perioperative setting and review the pathophysiology of α2-agonist overdose.

CASE SUMMARIES

Three patients accidentally received overdoses of dexmedetomidine, one intraoperatively (192 μg over 20 min) and 2 postoperatively (4 and 2 rather than 0.4 and 0.2 μg/kg/h; 0.5 μg/kg/min rather than 0.5 μg/kg/h). Hemodynamic parameters remained stable for all 3 patients. The most notable sign was oversedation diagnosed either clinically or using a bispectral index monitor; Naranjo criteria suggest possible or probable association of the reactions with dexmedetomidine. In all 3 cases, oversedation resolved within one hour of drug discontinuation. There were no other sequelae, and the remainder of each patient's hospital course was unremarkable.

DISCUSSION

As of this writing, dexmedetomidine dosing in excess of the label recommendation has been reported, but accidental dexmedetomidine overdose in clinical practice has not been described. Excessive levels of sedation were the only significant finding in all 3 patients. Dexmedetomidine's short redistribution half-life of 6 minutes should lead to rapid resolution of oversedation induced by overdoses if the overall duration of infusion is short (≤8 h). While the patients reported here were hemodynamically stable, dexmedetomidine may engender significant hemodynamic changes either because of sympatholysis at normal doses or vasoconstriction at higher than recommended doses. The absence of a significant hypertensive response to high dexmedetomidine concentrations suggests that dexmedetomidine-induced hypertension may be multifactorial, not simply related to plasma drug concentrations.

CONCLUSIONS

Practitioners presented with dexmedetomidine overdose should be prepared to manage oversedation. While hemodynamic alterations may be seen with dexmedetomidine use, hypertension from high dexmedetomidine plasma concentrations is not a consistent response. Practitioners using dexmedetomidine should carefully note that dosing for this agent is described by the manufacturer in μg/kg/h, not μg/kg/min.