Population Pharmacokinetics of Dexmedetomidine in Infants

Impact of anesthetics on rat hippocampus and neocortex: A comprehensive proteomic study based on label-free mass spectrometry

Anesthesia is regarded as an important milestone in medicine. However, the negative effect on memory and learning has been observed. In addition, the impact of anesthetics on postoperative cognitive functions is still discussed. In this work, in vivo experiment simulating a general anesthesia and ICU sedation was designed to assess the impact of two intravenous (midazolam, dexmedetomidine) and two inhalational (isoflurane, desflurane) agents on neuronal centers for cognition (neocortex), learning, and memory (hippocampus). More than 3600 proteins were quantified across both neocortex and hippocampus. Proteomic study revealed relatively mild effects of anesthetics, nevertheless, protein dysregulation uncovered possible different effect of isoflurane (and midazolam) compared to desflurane (and dexmedetomidine) to neocortical and hippocampal proteins. Isoflurane induced the upregulation of hippocampal NMDAR and other proteins of postsynaptic density and downregulation of GABA signaling, whereas desflurane and dexmedetomidine rather targeted mitochondrial VDAC isoforms and protein regulating apoptotic activity.

The effect of dexmedetomidine on expression of neuronal nitric oxide synthase in spinal dorsal cord in a rat model with chronic neuropathic pain

BACKGROUND

Neuropathic pain typically refers to the pain caused by somatosensory system injury or diseases, which is usually characterized by ambulatory pain, allodynia, and hyperalgesia. Nitric oxide produced by neuronal nitric oxide synthase (nNOS) in the spinal dorsal cord might serve a predominant role in regulating the algesia of neuropathic pain. The high efficacy and safety, as well as the plausible ability in providing comfort, entitle dexmedetomidine (DEX) to an effective anesthetic adjuvant. The aim of this study was to investigate the effect of DEX on the expression of nNOS in spinal dorsal cord in a rat model with chronic neuropathic pain.

METHODS

Male Sprague Dawley (SD) rats were randomly assigned into three groups: sham operation group (sham), (of the sciatic nerve) operation (CCI) group, and dexmedetomidine (DEX) group. Chronic neuropathic pain models in the CCI and DEX groups were established by sciatic nerve ligation. The thermal withdrawal latency (TWL) was measured on day 1 before operation and on day 1, 3, 7 and 14 after operation. Six animals were sacrificed after TWL measurement on day 7, and 14 days after operation, in each group, the L4-6 segment of the spinal cords was extracted for determination of nNOS expression by immunohistochemistry.

RESULTS

Compared with the sham group, the TWL threshold was significantly decreased and the expression of nNOS was up-regulated after operation in the CCI and DEX groups. Compared with the CCI grou[, the TWL threshold was significantly increased and the expression of nNOS was significantly down-regulated on day 7 and 14 days after operation in the DEX group.

CONCLUSION

Down-regulated nNOS in the spinal dorsal cord is involved in the attenuation of neuropathic pain by DEX.

Dexmedetomidine: An Alternative to Pain Treatment in Neonatology

Infants might be exposed to pain during their admissions in the neonatal intensive care unit [NICU], both from their underlying conditions and several invasive procedures required during their stay. Considering the particularities of this population, recognition and adequate management of pain continues to be a challenge for neonatologists and investigators. Diverse therapies are available for treatment, including non-pharmacological pain management measures and pharmacological agents (sucrose, opioids, midazolam, acetaminophen, topical agents…) and research continues. In recent years one of the most promising drugs for analgesia has been dexmedetomidine, an alpha-2 adrenergic receptor agonist. It has shown a promising efficacy and safety profile as it produces anxiolysis, sedation and analgesia without respiratory depression. Moreover, studies have shown a neuroprotective role in animal models which could be beneficial to neonatal population, especially in preterm newborns. Side effects of this therapy are mainly cardiovascular, but in most studies published, those were not severe and did not require specific therapeutic measures for their resolution. The main objective of this article is to summarize the existing literature on neonatal pain management strategies available and review the efficacy of dexmedetomidine as a new therapy with increasing use in the NICU.

Current Status of Pharmacokinetic Research in Children: A Systematic Review of Clinical Trial Records

BACKGROUND

Many medications have different pharmacokinetics in children than in adults. Knowledge about the safety and efficacy of medications in children requires research into the pharmacokinetic profiles of children's medicines. By analysing registered clinical trial records, this study determined how frequently pharmacokinetic data is gathered in paediatric drug trials.

METHODS

We searched for the pharmacokinetic data from clinical trial records for preterm infants and children up to the age of 16 from January 2011 to April 2022. The records of trials involving one or more drugs in preterm infants and children up to the age of 16 were examined for evidence that pharmacokinetic data would be collected.

RESULTS

In a total of 1483 records of interventional clinical trials, 136 (9.17%) pharmacokinetic data involved adults. Of those 136 records, 60 (44.1%) records were pharmacokinetics trials involving one or more medicines in children up to the age of 16. 20 (33.3 %) in America, followed by 19 (31.6 %) in Europe. Most trials researched medicines in the field of infection or parasitic diseases 20 (33.3%). 27 (48.2%) and 26 (46.4%) trials investigated medicines that were indicated as essential medicine.

CONCLUSION

The pharmacokinetic characteristics of children's drugs need to be better understood. The current state of pharmacokinetic research appears to address the knowledge gap in this area adequately. Despite slow progress, paediatric clinical trials have experienced a renaissance as the significance of paediatric trials has gained international attention. The outcome of paediatric trials will have an impact on children's health in the future. In recent years, the need for greater availability and access to safe child-size pharmaceuticals has received a lot of attention.

Dexmedetomidine - An emerging option for sedation in neonatal patients

Dexmedetomidine is a sedative agent with limited dosing, safety, and efficacy information in the neonatal population. This comprehensive review describes the available evidence summarizing the use of dexmedetomidine in various neonatal populations. We identified 21 studies and 1 case report supporting the efficacy and short-term safety of DEX in neonates. Reported dosing ranges from 0.5-1.5 mcg/kg/h with or without loading doses. Clinically relevant adverse effects include bradycardia and hypotension. Future studies are needed to determine long-term safety and facilitate clinical applicability.

Pharmacokinetic Pharmacodynamic Modelling Contributions to Improve Paediatric Anaesthesia Practice

The use of pharmacokinetic-pharmacodynamic models has improved anaesthesia practice in children through a better understanding of dose-concentration-response relationships, developmental pharmacokinetic changes, quantification of drug interactions and insights into how covariates (e.g., age, size, organ dysfunction, pharmacogenomics) impact drug prescription. Simulation using information from these models has enabled the prediction and learning of beneficial and adverse effects and decision-making around clinical scenarios. Covariate information, including the use of allometric size scaling, age and consideration of fat mass, has reduced population parameter variability. The target concentration approach has rationalised dose calculation. Paediatric pharmacokinetic-pharmacodynamic insights have led to better drug delivery systems for total intravenous anaesthesia and an expectation about drug offset when delivery is stopped. Understanding concentration-dependent adverse effects have tempered dose regimens. Quantification of drug interactions has improved the understanding of the effects of drug combinations. Repurposed drugs (e.g., antiviral drugs used for COVID-19) within the community can have important effects on drugs used in paediatric anaesthesia, and the use of simulation educates about these drug vagaries.

A retrospective comparative study of local anesthesia only and local anesthesia with sedation for percutaneous endoscopic lumbar discectomy

It is still an unsolved problem to achieve both immediate intraoperative feedback and satisfactory surgical experience in percutaneous endoscopic lumbar discectomy under local anesthesia for lumbar disk herniation (LDH) patients. Herein, we compared the analgesic and sedative effects of local anesthesia alone and local anesthesia with conscious sedation in LDH patients during percutaneous endoscopic lumbar discectomy. Ninety-two LDH patients were enrolled and divided into the following groups: control group (Con Group), dexmedetomidine group (Dex Group), oxycodone group (Oxy Group), and dexmedetomidine + oxycodone group (Dex + Oxy Group). Various signs, including mean arterial pressure (MAP), heart rate (HR), pulse oximeter oxygen saturation (SpO₂) and Ramsay score, were compared before anesthesia (T1), working cannula establishment (T2), nucleus pulposus removal (T3), and immediately postoperation (T4). Clinical outcomes, including VAS score, operation time, hospitalization period, Macnab criteria, and SF-36 score, were also evaluated. The Dex + Oxy Group showed the most stable MAP and HR at T2 and T3 in all groups. The clinical outcomes, such as VAS, hospitalization period, Macnab criteria, and SF-36 score, have no significant differences among groups (p > 0.05). Local anesthesia combined with conscious sedation is a safe and effective method to improve the surgical experience and achieve satisfying clinical outcomes for LDH patients during percutaneous endoscopic lumbar discectomy.

Best Evidence-Based Dosing Recommendations for Dexmedetomidine for Premedication and Procedural Sedation in Pediatrics: Outcome of a Risk-Benefit Analysis By the Dutch Pediatric Formulary

BACKGROUND

Dexmedetomidine is currently off-label for use in pediatric clinical care worldwide. Nevertheless, it is frequently prescribed to pediatric patients as premedication prior to induction of anesthesia or for procedural sedation. There is ample literature on the pharmacokinetics, efficacy and safety of dexmedetomidine in this vulnerable patient population, but there is a general lack of consensus on dosing. In this project, we aimed to use the standardized workflow of the Dutch Pediatric Formulary to establish best evidence-based pediatric dosing guidelines for dexmedetomidine as premedication and for procedural sedation.

METHOD

The available literature on dexmedetomidine in pediatrics was reviewed in order to address the following three questions: (1) What is the right dose? (2) What is known about efficacy? (3) What is known about safety? Relevant literature was compiled into a risk-benefit analysis document. A team of clinical experts critically appraised the analysis and the proposed dosing recommendations.

RESULTS

Dexmedetomidine is most commonly administered via the intravenous or intranasal route. Clearance is age dependent, warranting higher doses in infants to reach similar exposure as in adults. Dexmedetomidine use results in satisfactory sedation at parent separation, adequate sedation and a favorable recovery profile. The safety profile is good and comparable to adults, with dose-related hemodynamic effects.

CONCLUSION

Following the structured approach of the Dutch Pediatric Formulary, best evidence-based dosing recommendations were proposed for dexmedetomidine, used as premedication prior to induction of anesthesia (intranasal dose) and for procedural sedation (intranasal and intravenous dose) in pediatric patients.

The effect of dexmedetomidine on neuroprotection in pediatric cardiac surgery patients: study protocol for a prospective randomized controlled trial

Background

Infants undergoing cardiac surgery under cardiopulmonary bypass are vulnerable to postoperative neurodevelopmental delays. Dexmedetomidine has been shown to have protective effects on the heart, kidneys, and brain in animals and adults undergoing cardiac surgery with cardiopulmonary bypass. We hypothesized that dexmedetomidine would have a neuroprotective effect on infants undergoing cardiopulmonary bypass and planned a prospective randomized controlled trial with postoperative neurodevelopment measurements.

Methods

This is a single-center, prospective, double-blinded, randomized controlled trial with 1:1 allocation. A cohort of 160 infants undergoing cardiac surgery with cardiopulmonary bypass will be enrolled. After induction, dexmedetomidine will be infused with a loading dose of 1 μg/kg and a maintenance dose of 0.5 μg/kg/h or the same amount of normal saline will be administered. Upon initiation of cardiopulmonary bypass, an additional dose of dexmedetomidine (0.01 μg/cardiopulmonary priming volume) will be mixed with the cardiopulmonary bypass circuit. The primary outcome will be the proportion of infants who score lower than 85 in any of the cognitive, language, or motor Bayley scales of infant development-III tests 1 year after the surgery. Other feasible outcome measures will include differences in plasma glial fibrillary acidic protein, troponin I, interleukin-6, urinary neutrophil gelatinase-associated lipocalin, and perioperative major adverse events. The results of the Bayley scales of infant development-III test from the study group and the control group will be compared using a chi-squared test under intention-to-treat analysis. A generalized estimating equation will be used to analyze repeated measurements over time.

Discussion

This study will enable us to assess whether the use of dexmedetomidine can alter the early neurodevelopmental outcome in infants undergoing cardiac surgery with cardiopulmonary bypass and also estimate effects of dexmedetomidine on other organs.

Trial registration

ClinicalTrials.gov NCT04484922. Registered on 24 July 2020

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06217-9.

Dexmedetomidine in Children on Extracorporeal Membrane Oxygenation: Pharmacokinetic Data Exploration Using Previously Published Models

BACKGROUND

Dexmedetomidine is a sedative and analgesic increasingly used in children supported with extracorporeal membrane oxygenation (ECMO). No data is available to describe the pharmacokinetics (PK) of dexmedetomidine in this population.

METHODS

We performed a single-center prospective PK study. Children <18 years old, supported with ECMO, and on a dexmedetomidine infusion as part of their management were prospectively included. PK samples were collected. Dexmedetomidine dosing remained at the discretion of the clinical team. Six population PK models built in pediatrics were selected. Observed concentrations were compared with population predicted concentrations using the PK models.

RESULTS

Eight children contributed 30 PK samples. None of the PK models evaluated predicted the concentrations with acceptable precision and bias. Four of the six evaluated models overpredicted the concentrations. The addition of a correction factor on clearance improved models' fit. Two of the evaluated models were not applicable to our whole population age range because of their structure.

CONCLUSION

Most of the evaluated PK models overpredicted the concentrations, potentially indicating increased clearance on ECMO. Population PK models applicable to a broad spectrum of ages and pathologies are more practical in pediatric critical care settings but challenging to develop.

Medication Use in the Neonatal Intensive Care Unit and Changes from 2010 to 2018

OBJECTIVE

To provide up-to-date medication prescribing patterns in US neonatal intensive care units (NICUs) and to examine trends in prescribing patterns over time.

STUDY DESIGN

We performed a cohort study of 799 016 infants treated in NICUs managed by the Pediatrix Medical Group from 2010 to 2018. We used 3 different methods to report counts of medication: exposure, courses, and days of use. We defined the change in frequency of medication administration by absolute change and relative change. We examined the Food and Drug Administration (FDA) package insert for each medication to determine whether a medication was labeled for use in infants and used PubMed to search for pharmacokinetics (PK) studies.

RESULTS

The most frequently prescribed medications included ampicillin, gentamicin, caffeine citrate, poractant alfa, morphine, vancomycin, furosemide, fentanyl, midazolam, and acetaminophen. Of the top 50 medications used in infants with extremely low birth weight, only 20 (40%) are FDA-labeled for use in infants; of the 30 that are not labeled for use in infants, 13 (43%) had at least 2 published PK studies. The medications with the greatest relative increase in use from 2010 to 2018 included dexmedetomidine, clonidine, rocuronium, levetiracetam, atropine, and diazoxide. The medications with the greatest relative decrease in use included tromethamine acetate, pancuronium, chloral hydrate, imipenem + cilastatin, and amikacin.

CONCLUSION

Trends of medication use in the NICU change substantially over time. It is imperative to identify changes in medication use in the NICU to better inform further prospective studies.

Population Pharmacokinetic Analysis of Dexmedetomidine in Children using Real World Data from Electronic Health Records and Remnant Specimens

AIM

Our objectives were to perform a population pharmacokinetic analysis of dexmedetomidine in children using remnant specimens and electronic health records (EHRs) and explore the impact of patient's characteristics and pharmacogenetics on dexmedetomidine clearance.

METHODS

Dexmedetomidine dosing and patient data were gathered from EHRs and combined with opportunistically sampled remnant specimens. Population pharmacokinetic models were developed using nonlinear mixed-effects modeling. Stage one developed a model without genotype variables; Stage two added pharmacogenetic effects.

RESULTS

Our final study population included 354 post-cardiac surgery patients age 0 to 22 years (median 16 months). The data were best described with a two-compartment model with allometric scaling for weight and Hill maturation function for age. Population parameter estimates and 95% confidence intervals were 27.3 L/hr (24.0 - 31.1 L/hr) for total clearance (CL), 161 L (139 - 187 L) for central compartment volume of distribution (V₁ ), 26.0 L/hr (22.5 - 30.0 L/hr) for intercompartmental clearance (Q), and 7903 L (5617 - 11119 L) for peripheral compartment volume of distribution (V₂ ). The estimate for postmenstrual age when 50% of adult clearance is achieved was 42.0 weeks (41.5 - 42.5 weeks) and the Hill coefficient estimate was 7.04 (6.99 - 7.08). Genotype was not statistically or clinically significant.

CONCLUSION

Our study demonstrates the use of real-world EHR data and remnant specimens to perform a population PK analysis and investigate covariate effects in a large pediatric population. Weight and age were important predictors of clearance. We did not find evidence for pharmacogenetic effects of UGT1A4 or UGT2B10 genotype or CYP2A6 risk score.

Pediatric Palliative Care Pharmacy Pearls—A Focus on Pain and Sedation

Determining the optimal dosing regimen for pediatric patients is a challenge due to the lack of dosing guidelines and studies. In addition, many developmental pharmacology changes that occur throughout childhood that have profound impacts on the absorption, distribution, metabolism, and elimination of medications are commonly used in palliative care. Adding to that complexity, certain medications have different effects in the pediatric patient compared to the adult patient. Being aware of the pharmacokinetic changes, impact on neurodevelopment and unique medication factors that are present in pediatric patients helps clinicians treat the pediatric palliative care patient in the best and safest way possible.

Population Modelling of Dexmedetomidine Pharmacokinetics and Haemodynamic Effects After Intravenous and Subcutaneous Administration

Background and Objective

Dexmedetomidine is a potent agonist of α₂-adrenoceptors causing dose-dependent sedation in humans. Intravenous dexmedetomidine is commonly used perioperatively, but an extravascular route of administration would be favoured in palliative care. Subcutaneous infusions provide desired therapeutic plasma concentrations with fewer unwanted effects as compared with intravenous dosing. We aimed to develop semi-mechanistic population models for predicting pharmacokinetic and pharmacodynamic profiles of dexmedetomidine after intravenous and subcutaneous dosing.

Methods

Non-linear mixed-effects modelling was performed using previously collected concentration and haemodynamic effects data from ten (eight in the intravenous phase) healthy human subjects, aged 19–27 years, receiving 1 µg/kg of intravenous or subcutaneous dexmedetomidine during a 10-min infusion.

Results

The absorption of dexmedetomidine from the subcutaneous injection site, and distribution to local subcutaneous fat tissue was modelled using a semi-physiological approach consisting of a depot and fat compartment, while a two-compartment mammillary model explained further disposition. Dexmedetomidine-induced reductions in plasma norepinephrine concentrations were accurately described by an indirect response model. For blood pressure models, the net effect was specified as hyper- and hypotensive effects of dexmedetomidine due to vasoconstriction on peripheral arteries and sympatholysis mediated via the central nervous system, respectively. A heart rate model combined the dexmedetomidine-induced sympatholytic effect, and input from the central nervous system, predicted from arterial blood pressure levels. Internal evaluation confirmed the predictive performance of the final models, as well as the accuracy of the parameter estimates with narrow confidence intervals.

Conclusions

Our final model precisely describes dexmedetomidine pharmacokinetics and accurately predicts dexmedetomidine-induced sympatholysis and other pharmacodynamic effects. After subcutaneous dosing, dexmedetomidine is taken up into subcutaneous fat tissue, but our simulations indicate that accumulation of dexmedetomidine in this compartment is insignificant.

ClinicalTrials.org

NCT02724098 and EudraCT 2015-004698-34

Electronic supplementary material

The online version of this article (10.1007/s40262-020-00900-3) contains supplementary material, which is available to authorized users.

Pharmacokinetic concepts for dexmedetomidine target-controlled infusion pumps in children

Pharmacokinetic parameter estimates are used in mathematical equations (pharmacokinetic models) to describe concentration changes with time in a population and are specific to that population. Simulation using these models and their parameter estimates can enrich understanding of drug behavior and serve as a basis for study design. Pharmacokinetic concepts are presented pertaining to future designs of dexmedetomidine target-controlled infusion pumps in children. This manuscript provides the pediatric anesthesiologist with an understanding of the nuances that should be considered when using target-controlled infusion pumps; how the central volume may differ between populations, how clearance changes with age, and the impact of adverse effects on dose. In addition, the ideal loading dose and rate of delivery to achieve target concentration without adverse cardiovascular effects are reviewed, and finally, dose considerations for obese children, based on contact-sensitive half-time, are introduced. An understanding of context-sensitive half-time changes with age enables anesthetic practitioners to better estimate duration of effect after cessation of dexmedetomidine infusion. Use of these known pharmacokinetic parameters and covariate information for the pediatric patient could readily be incorporated into commercial target-controlled infusion pumps to allow effective and safe open-loop administration of dexmedetomidine in children.

Emerging therapies and management for neonatal encephalopathy-controversies and current approaches

Neonatal encephalopathy (NE) continues to have a major impact on newborn survival and neurodevelopmental outcomes worldwide. In high-income settings, therapeutic hypothermia is the only established standard treatment for neonates with moderate-to-severe NE, with compelling evidence that cooling reduces mortality and major neurodevelopmental impairment in survivors. Despite therapeutic hypothermia, a significant proportion of cooled infants continue to suffer long-term disability from brain injury. Innovative therapies offer the possibility of further improving neurodevelopmental outcomes by working synergistically with therapeutic hypothermia to decrease hypoxia-ischemia-induced excitotoxicity, prevent progression to secondary energy failure, and in some cases, promote neuroregeneration in the developing neonatal brain. This review discusses emerging NE therapies currently under investigation, offers insight into controversies surrounding various approaches to clinical care during therapeutic hypothermia, and identifies ongoing knowledge deficits that hinder attainment of optimal outcomes for neonates with NE.

A Universal Pharmacokinetic Model for Dexmedetomidine in Children and Adults

A universal pharmacokinetic model was developed from pooled paediatric and adult data (40.6 postmenstrual weeks, 70.8 years, 3.1-152 kg). A three-compartment pharmacokinetic model with first-order elimination was superior to a two-compartment model to describe these pooled dexmedetomidine data. Population parameter estimates (population parameter variability%) were clearance (CL) 0.9 L/min/70 kg (36); intercompartmental clearances (Q2) 1.68 L/min/70 kg (63); Q3 0.62 L/min/70 kg (90); volume of distribution in the central compartment (V1) 25.2 L/70 kg (103.9); rapidly equilibrating peripheral compartment (V2) 34.4 L/70 kg (41.8); slow equilibrating peripheral compartment (V3) 65.4 L/70 kg (62). Obesity was best described by fat-free mass for clearances and normal fat mass for volumes with a factor for fat mass (FfatV) of 0.293. Models describing dexmedetomidine pharmacokinetics in adults can be applied to children by accounting for size (allometry) and age (maturation). This universal dexmedetomidine model is applicable to a broad range of ages and weights: neonates through to obese adults. Lean body weight is a better size descriptor for dexmedetomidine clearance than total body weight. This parameter set could be programmed into target-controlled infusion pumps for use in a broad population.

Dexmedetomidine: What's New for Pediatrics? A Narrative Review

Over the past few years, despite the lack of approved pediatric labelling, dexmedetomidine’s (DEX) use has become more prevalent in pediatric clinical practice as well as in research trials. Its respiratory-sparing effects and bioavailability by various routes are only some of the valued features of DEX. In recent years the potential organ-protective effects of DEX, with the possibility for preserving neurocognitive function, has put it in the forefront of clinical and bench research. This comprehensive review focused on the pediatric literature but presents relevant, supporting adult and animal studies in order to detail the recent growing body of literature around the pharmacology, end-organ effects, organ-protective effects, alternative routes of administration, synergetic effects, and clinical applications, with considerations for the future.

Opioids and alpha-2-agonists for analgesia and sedation in newborn infants: protocol of a systematic review

BACKGROUND

Hospitalized newborn infants may require analgesia and sedation either for the management of procedural pain, during or after surgery, and other painful conditions. The benefits and harms of opioids administered at different doses and routes of administration have been reported in numerous trials and systematic reviews. The use of alpha-2-agonists such as clonidine and dexmedetomidine in newborn infants is more recent, and they might be prescribed to reduce the total amount of opioids which are thought to have more side effects. Moreover, alpha-2-agonists might play an important role in the management of agitation and discomfort.

METHODS

We will conduct a systematic review and meta-analysis on the use of opioids, alpha-2-agonists, or the combination of both drugs. We will include randomized controlled trials to assess benefits and harms and observational studies to assess adverse events and pharmacokinetics; preterm and term infants; studies on any opioids or alpha-2-agonists administered for any indication and by any route except spinal, intraosseous, or administration for nerve blocks and wound infusions. The use of opioids or alpha-2-agonists will be compared to no intervention; placebo with normal saline or other non-sedative, non-analgesic drug; control with oral sugar solution or non-pharmacological intervention; same drug of different dose or route; or a different drug (not limiting to opioids and alpha-2-agonists) or combinations of such drugs. The primary outcomes for this review will be all-cause mortality during initial hospitalization and hypotension requiring medical therapy. We will conduct a search in the following databases: The Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), MEDLINE, Embase, and CINAHL. Two review authors will independently screen records for inclusion, undertake data abstraction using a data extraction form and assess the risk of bias of all included trials using the Cochrane "Risk of bias" tool.

DISCUSSION

This systematic review will summarize and update our knowledge about neonatal analgesia and sedation including pharmacokinetics/pharmacodynamics, and provide a platform for developing evidence-based guidelines that we can immediately apply to our clinical practice.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO 2020 CRD42020170852.

Mechanisms of Dexmedetomidine in Neuropathic Pain

Dexmedetomidin is a new-generation, highly selective α2 adrenergic receptor agonist with a large number of advantages, including its sedative and analgesic properties, its ability to inhibit sympathetic nerves, its reduced anesthetic dosage, its hemodynamic stability, its mild respiratory depression abilities, and its ability to improve postoperative recognition. Its safety and effectiveness, as well as its ability to provide a certain degree of comfort to patients, make it a useful anesthetic adjuvant for a wide range of clinical applications. For example, dexmedetomidine is commonly used in patients undergoing general anesthesia, and it also exerts sedative effects during tracheal intubation or mechanical ventilation in intensive care unit patients. In recent years, with the deepening of clinical research on dexmedetomidine, the drug is still applied in the treatment of spastic pain, myofascial pain, neuropathic pain, complex pain syndrome, and chronic headache, as well as for multimodal analgesia. However, we must note that the appropriateness of patient and dose selection should be given attention when using this drug; furthermore, patients should be observed for adverse reactions such as hypotension and bradycardia. Therefore, the safety and effectiveness of this drug for long-term use remain to be studied. In addition, basic experimental studies have also found that dexmedetomidine can protect important organs, such as the brain, heart, kidney, liver, and lung, through various mechanisms, such as antisympathetic effects, the inhibition of apoptosis and oxidative stress, and a reduction in the inflammatory response. Moreover, the neuroprotective properties of dexmedetomidine have received the most attention from scholars. Hence, in this review, we mainly focus on the characteristics and clinical applications of dexmedetomidine, especially the role of dexmedetomidine in the nervous system and the use of dexmedetomidine in the relief of neuropathic pain.

Pharmacokinetics of Dexmedetomidine in Infants and Children After Orthotopic Liver Transplantation

BACKGROUND

Dexmedetomidine (DEX) is a sedative and analgesic medication that is frequently used postoperatively in children after liver transplantation. Hepatic dysfunction, including alterations in drug clearance, is common immediately after liver transplantation. However, the pharmacokinetics (PK) of DEX in this population is unknown. The objective of this study was to determine the PK profile of DEX in children after liver transplantation.

METHODS

This was a single-center, open-label PK study of DEX administered as an intravenous loading dose of 0.5 μg/kg followed by a continuous infusion of 0.5 μg/kg/h. Twenty subjects, 1 month to 18 years of age, who were admitted to the pediatric intensive care unit after liver transplantation were enrolled. Whole blood was collected and analyzed for DEX concentration using a dried blood spot method. Nonlinear mixed-effects modeling was used to characterize the population PK of DEX.

RESULTS

DEX PK was best described by a 2-compartment model with first-order elimination. A typical child after liver transplantation with an international normalized ratio (INR) of 1.8 was found to have a whole blood DEX clearance of 52 L/h (95% confidence interval [CI], 31-73 L/h). In addition, intercompartmental clearance was 246 L/h (95% CI, 139-391 L/h), central volume of distribution was 186 L/70 kg (95% CI, 140-301 L/70 kg), and peripheral volume of distribution was 203 L (95% CI, 123-338 L). Interindividual variability ranged from 11% to 111% for all parameters. Clearance was not found to be associated with weight but was found to be inversely proportional to INR. An increase in INR to 3.2 resulted in a 50% decrease in DEX clearance. Weight was linearly correlated with central volume of distribution. All other covariates, including age, ischemic time, total bilirubin, and alanine aminotransferase, were not found to be significant predictors of DEX disposition.

CONCLUSIONS

Children who received DEX after liver transplantation have large variability in clearance, which was not found to be associated with weight but is influenced by underlying liver function, as reflected by INR. In this population, titration of DEX dosing to clinical effect may be important because weight-based dosing is poorly associated with blood concentrations. More attention to quality of DEX sedation may be warranted when INR values are changing.

Dexmedetomidine extraction by the extracorporeal membrane oxygenation circuit: results from an in vitro study

BACKGROUND

Dexmedetomidine is a sedative administered to minimize distress and decrease the risk of life threatening complications in children supported with extracorporeal membrane oxygenation. The extracorporeal membrane oxygenation circuit can extract drug and decrease drug exposure, placing the patient at risk of therapeutic failure.

OBJECTIVE

To determine the extraction of dexmedetomidine by the extracorporeal membrane oxygenation circuit.

MATERIALS AND METHODS

Dexmedetomidine was studied in three closed-loop circuit configurations to isolate the impact of the oxygenator, hemofilter, and tubing on circuit extraction. Each circuit was primed with human blood according to standard practice for Duke Children's Hospital, and flow was set to 1 L/min. Dexmedetomidine was dosed to achieve a therapeutic concentration of ~600 pg/mL. Dexmedetomidine was added to a separate tube of blood to serve as a control and evaluate for natural drug degradation. Serial blood samples were collected over 24 hours and concentrations were quantified with a validated assay. Drug recovery was calculated at each time point.

RESULTS

Dexmedetomidine was highly extracted by the oxygenator evidenced by a mean recovery of 62-67% at 4 hours and 23-34% at 24 hours in circuits with an oxygenator in-line. In contrast, mean recovery with the oxygenator removed was 96% at 4 hours and 93% at 24 hours. Dexmedetomidine was stable over time with a mean recovery in the control samples of 102% at 24 hours.

CONCLUSION

These results suggest dexmedetomidine is extracted by the oxygenator in the extracorporeal membrane oxygenation circuit which may result in decreased drug exposure in vivo.

Dexmedetomidine Pharmacokinetics in Neonates with Hypoxic-Ischemic Encephalopathy Receiving Hypothermia

Dexmedetomidine is a promising sedative and analgesic for newborns with hypoxic-ischemic encephalopathy (HIE) undergoing therapeutic hypothermia (TH). Pharmacokinetics and safety of dexmedetomidine were evaluated in a phase I, single-center, open-label study to inform future trial strategies. We recruited 7 neonates ≥36 weeks' gestational age diagnosed with moderate-to-severe HIE, who received a continuous dexmedetomidine infusion during TH and the 6 h rewarming period. Time course of plasma dexmedetomidine concentration was characterized by serial blood sampling during and after the 64.8 ± 6.9 hours of infusion. Noncompartmental analysis yielded descriptive pharmacokinetic estimates: plasma clearance of 0.760 ± 0.155 L/h/kg, steady-state distribution volume of 5.22 ± 2.62 L/kg, and mean residence time of 6.84 ± 3.20 h. Naive pooled and population analyses according to a one-compartment model provided similar estimates of clearance and distribution volume. Overall, clearance was either comparable or lower, distribution volume was larger, and mean residence time or elimination half-life was longer in cooled newborns with HIE compared to corresponding estimates previously reported for uncooled (normothermic) newborns without HIE at comparable gestational and postmenstrual ages. As a result, plasma concentrations in cooled newborns with HIE rose more slowly in the initial hours of infusion compared to predicted concentration-time profiles based on reported pharmacokinetic parameters in normothermic newborns without HIE, while similar steady-state levels were achieved. No acute adverse events were associated with dexmedetomidine treatment. While dexmedetomidine appeared safe for neonates with HIE during TH at infusion doses up to 0.4 μg/kg/h, a loading dose strategy may be needed to overcome the initial lag in rise of plasma dexmedetomidine concentration.

Dexmedetomidine Pharmacokinetics and a New Dosing Paradigm in Infants Supported With Cardiopulmonary Bypass

BACKGROUND

Dexmedetomidine is increasingly used off-label in infants and children with cardiac disease during cardiopulmonary bypass (CPB) and in the postoperative period. Despite its frequent use, optimal dosing of dexmedetomidine in the setting of CPB has not been identified but is expected to differ from dosing in those not supported with CPB. This study had the following aims: (1) characterize the effect of CPB on dexmedetomidine clearance (CL) and volume of distribution (V) in infants and young children; (2) characterize tolerance and sedation in patients receiving dexmedetomidine; and (3) identify preliminary dosing recommendations for infants and children undergoing CPB. We hypothesized that CL would decrease, and V would increase during CPB compared to pre- or post-CPB states.

METHODS

Open-label, single-center, opportunistic pharmacokinetics (PK) and safety study of dexmedetomidine in patients ≤36 months of age administered dexmedetomidine per standard of care via continuous infusion. We analyzed dexmedetomidine PK data using standard nonlinear mixed effects modeling with NONMEM software. We compared model-estimated PK parameters to those from historical patients receiving dexmedetomidine before anesthesia for urologic, lower abdominal, or plastic surgery; after low-risk cardiac or craniofacial surgery; or during bronchoscopy or nuclear magnetic resonance imaging. We investigated the influence of CPB-related factors on PK estimates and used the final model to simulate dosing recommendations, targeting a plasma concentration previously associated with safety and efficacy (0.6 ng/mL). We used the Wilcoxon rank sum test to evaluate differences in dexmedetomidine exposure between infants with hypotension or bradycardia and those who did not develop these adverse events.

RESULTS

We collected 213 dexmedetomidine plasma samples from 18 patients. Patients had a median (range) age of 3.3 months (0.1-34.0 months) and underwent CPB for 161 minutes (63-394 minutes). We estimated a CL of 13.4 L/h/70 kg (95% confidence interval, 2.6-24.2 L/h/70 kg) during CPB, compared to 42.1 L/h/70 kg (95% confidence interval, 38.7-45.8 L/h/70 kg) in the historical patients. No specific CPB-related factor had a statistically significant effect on PK. A loading dose of 0.7 µg/kg over 10 minutes before CPB, followed by maintenance infusions through CPB of 0.2 or 0.25 µg/kg/h in infants with postmenstrual ages of 42 or 92 weeks, respectively, maintained targeted concentrations. We identified no association between dexmedetomidine exposure and selected adverse events (P = .13).

CONCLUSIONS

CPB is associated with lower CL during CPB in infants and young children compared to those not undergoing CPB. Further study should more closely investigate CPB-related factors that may influence CL.

A Population Pharmacokinetic Model of Intravenous Dexmedetomidine for Mechanically Ventilated Children after Neurosurgery

Dexmedetomidine is a selective alpha-2 adrenergic agonist with concurrent sedative and analgesic effects, and it is being increasingly used in pediatric anesthesia and intensive care. This study aimed to investigate the pharmacokinetics of intravenous dexmedetomidine in mechanically ventilated children in the intensive care unit (ICU) after neurosurgery. Pediatric patients aged 2–12 years, who were mechanically ventilated in ICU after neurosurgery, were allocated into a low-dose (n = 15) or high-dose (n = 14) group. The low-dose group received dexmedetomidine at a loading dose of 0.25 µg/kg for 10 min, followed by a maintenance dose of 0.25 µg/kg/h for 50 min, whereas the high-dose group received dexmedetomidine at a loading dose of 0.5 µg/kg for 10 min, followed by a maintenance dose of 0.5 µg/kg/h for 50 min. Serial blood samples were collected for a pharmacokinetic analysis up to 480 min after the end of the infusion. The sedative effect of dexmedetomidine was assessed using the Bispectral Index and University of Michigan Sedation Scale. Adverse reactions, electrocardiography findings, and vital signs were monitored for a safety assessment. A population pharmacokinetic analysis was performed using non-linear mixed effects modeling. Dexmedetomidine induced a moderate-to-deep degree of sedation during infusion in both groups. The pharmacokinetics of dexmedetomidine were best described by a two-compartment disposition model with first-order elimination kinetics. The parameters were standardized for a body weight of 70 kg using an allometric power model. The population estimates (95% confidence interval) per 70 kg body weight were as follows: clearance of 81.0 (72.9–90.9) L/h, central volume of distribution of 64.2 (50.6–81.0) L, intercompartment clearance of 116.4 (90.6–156.0) L/h, and peripheral volume of distribution of 167 (132–217) L. No serious adverse reactions or hemodynamic changes requiring the discontinuation of dexmedetomidine were observed. Dexmedetomidine had increased clearance and volume of distribution in mechanically ventilated children in ICU after neurosurgery, thereby indicating the need to adjust the dosage to obtain a target plasma concentration.

Dose rationale and pharmacokinetics of dexmedetomidine in mechanically ventilated new-borns: impact of design optimisation

PURPOSE

There is a need for alternative analgosedatives such as dexmedetomidine in neonates. Given the ethical and practical difficulties, protocol design for clinical trials in neonates should be carefully considered before implementation. Our objective was to identify a protocol design suitable for subsequent evaluation of the dosing requirements for dexmedetomidine in mechanically ventilated neonates.

METHODS

A published paediatric pharmacokinetic model was used to derive the dosing regimen for dexmedetomidine in a first-in-neonate study. Optimality criteria were applied to optimise the blood sampling schedule. The impact of sampling schedule optimisation on model parameter estimation was assessed by simulation and re-estimation procedures for different simulation scenarios. The optimised schedule was then implemented in a neonatal pilot study.

RESULTS

Parameter estimates were more precise and similarly accurate in the optimised scenarios, as compared to empirical sampling (normalised root mean square error: 1673.1% vs. 13,229.4% and relative error: 46.4% vs. 9.1%). Most importantly, protocol deviations from the optimal design still allowed reasonable parameter estimation. Data analysis from the pilot group (n = 6) confirmed the adequacy of the optimised trial protocol. Dexmedetomidine pharmacokinetics in term neonates was scaled using allometry and maturation, but results showed a 20% higher clearance in this population compared to initial estimates obtained by extrapolation from a slightly older paediatric population. Clearance for a typical neonate, with a post-menstrual age (PMA) of 40 weeks and weight 3.4 kg, was 2.92 L/h. Extension of the study with 11 additional subjects showed a further increased clearance in pre-term subjects with lower PMA.

CONCLUSIONS

The use of optimal design in conjunction with simulation scenarios improved the accuracy and precision of the estimates of the parameters of interest, taking into account protocol deviations, which are often unavoidable in this event-prone population.