Sensitive and specific liquid chromatography–tandem mass spectrometric method for the quantitation of dexmedetomidine in pediatric plasma

Dose Escalation Pharmacokinetic Study of Intranasal Atomized Dexmedetomidine in Pediatric Patients With Congenital Heart Disease

BACKGROUND

Atomized intranasal dexmedetomidine is an attractive option when sedation is required for pediatric patients as either premedication or the sole agent for noninvasive, nonpainful procedures. While intranasal dexmedetomidine is used frequently in this population, it is still unclear what dose and time of administration relative to the procedure will result in the optimal effect. Knowledge regarding the maximum concentration (C max ) and time to reach maximum concentration (T max ) of intranasally administered dexmedetomidine is the first step toward this. The risk of hemodynamic instability caused by increasing doses of dexmedetomidine necessitates a greater understanding of the pharmacokinetics in children.

METHODS

Sixteen pediatric patients 2 to 6 years of age undergoing elective cardiac catheterization received 2 or 4 μg/kg dexmedetomidine intranasally. Plasma concentrations were determined by liquid chromatography-tandem mass spectrometry with a validated assay. Descriptive noncompartmental analysis provided estimates of peak concentrations and time to reach peak concentrations. A population pharmacokinetic model was developed using nonlinear mixed-effects modeling. Simulations were performed using the final model to assess dose concentrations with an alternative dosing regimen of 3 µg/kg.

RESULTS

A median peak plasma concentration of 413 pg/mL was achieved 91 minutes after 2 μg/kg dosing, and a median peak plasma concentration of 1000 pg/mL was achieved 54 minutes after 4 μg/kg dosing. A 1-compartment pharmacokinetic model adequately described the data. Three subjects in the 4 μg/kg dosing cohort achieved a dose-limiting toxicity (DLT), defined as a plasma dexmedetomidine concentration >1000 pg/mL. None of these subjects had any significant hemodynamic consequences. Simulations showed that no subjects would experience a level >1000 pg/mL when using a dose of 3 µg/kg.

CONCLUSIONS

Concentrations associated with adequate sedation can be achieved with intranasal dexmedetomidine doses of 2 to 4 µg/kg in children 2 to 6 years of age. However, 50% of our evaluable subjects in this cohort reached a plasma concentration >1000 pg/mL. Doses of 3 µg/kg may be optimal in this population, with simulated concentrations remaining below this previously established toxicity threshold. Further studies correlating concentrations with efficacy and adverse effects are needed.

Simultaneous detection of a panel of nine sedatives and metabolites in plasma from critically ill pediatric patients via UPLC-MS/MS

Sedative use can result in adverse drug reactions. Intensive care unit patients are especially at risk and pharmacokinetic modeling of drug concentrations is an approach to develop precision dosing strategies. However, limited blood sampling availability in critically ill children and need for multiple assays to quantify a variety of commonly used sedatives creates logistical challenges. The goal of this project was to develop a sensitive and selective assay for the simultaneous quantification of a panel of sedatives comprised of midazolam (MDZ), alpha hydroxymidazolam (1- OH MDZ), dexmedetomidine (DEX), morphine (MOR), morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G), fentanyl (FEN), norfentanyl (NF), and hydromorphone (HM) in small volume pediatric plasma samples. A sensitive and efficient ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS/MS) method was developed following FDA guidance for bioanalytical validation. Minimal sample preparation consisting of simple protein precipitation extraction using acetonitrile with internal standards was utilized. Analyte separation was achieved using a gradient mixture of (A: 0.15% formic acid in water and B: Acetonitrile) and a Waters Acquity C18, 1.7 µm (2.1 × 100 mm) column. Assays were linear over the clinical concentration ranges: MDZ, MOR, HM: 0.5-125 ng/mL; 1-OH MDZ, M3G, M6G: 5-500 ng/mL; and DEX, FEN, NF: 0.05-7.5 ng/mL (R2 > 0.99 for all). Assay run time was 10 min and required only 100 μL of plasma. Initial testing of samples from pediatric patients demonstrates adequacy of assay to measure sedatives and metabolites at clinical concentrations confidently in low volumes of plasma. This novel highly-sensitive and specific method to measure a total of nine different analytes (five sedatives, four metabolites) simultaneously enables comprehensive analysis of a panel of sedatives in small volumes such as in pediatric ICU patients.

Results of a phase 1 multicentre investigation of dexmedetomidine bolus and infusion in corrective infant cardiac surgery

BACKGROUND

Dexmedetomidine (DEX) is increasingly used intraoperatively in infants undergoing cardiac surgery. This phase 1 multicentre study sought to: (i) determine the safety of DEX for cardiac surgery with cardiopulmonary bypass; (ii) determine the pharmacokinetics (PK) of DEX; (iii) create a PK model and dosing for steady-state DEX plasma levels; and (iv) validate the PK model and dosing.

METHODS

We included 122 neonates and infants (0-180 days) with D-transposition of the great arteries, ventricular septal defect, or tetralogy of Fallot. Dose escalation was used to generate NONMEM® PK modelling, and then validation was performed to achieve low (200-300 pg ml-1), medium (400-500 pg ml-1), and high (600-700 pg ml-1) DEX plasma concentrations.

RESULTS

Five of 122 subjects had adverse safety outcomes (4.1%; 95% confidence interval [CI], 1.8-9.2%). Two had junctional rhythm, two had second-/third-degree atrioventricular block, and one had hypotension. Clearance (CL) immediately postoperative and CL on CPB were reduced by approximately 50% and 95%, respectively, compared with pre-CPB CL. DEX clearance after CPB was 1240 ml min-1 70 kg-1. Age at 50% maximum clearance was approximately 2 days, and that at 90% maximum clearance was 18 days. Overall, 96.1% of measured DEX concentrations fell within the 5th-95th percentile prediction intervals in the PK model validation. Dosing strategies are recommended for steady-state DEX plasma levels ranging from 200 to 1000 pg ml-1.

CONCLUSIONS

When used with a careful dosing strategy, DEX results in low incidence and severity of adverse safety events in infants undergoing cardiac surgery with cardiopulmonary bypass. This validated PK model should assist clinicians in selecting appropriate dosing. The results of this phase 1 trial provide preliminary data for a phase 3 trial of DEX neuroprotection.

CLINICAL TRIALS REGISTRATION

NCT01915277.

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.

An improved ultra-high-performance liquid chromatography-tandem mass spectrometric method for the quantitation of dexmedetomidine in small volume of pediatric plasma

Dexmedetomidine (Dex), a highly selective α₂ -adrenergic agonist, is used primarily for the sedation and anxiolysis of adults and children in the intensive care setting. A sensitive and selective assay for Dex in pediatric plasma was developed by employing ultra-high-performance liquid chromatography-tandem mass spectrometry with d4-Dex as an internal standard. Dex was extracted from 0.1 mL of plasma by micro-elution solid-phase extraction. Separation was achieved with a Waters XBridge C₁₈ column with a flow rate of 0.3 mL/min using a mobile phase comprising 5 mm ammonium acetate buffer with 0.03% formic acid in water and methanol-acetonitrile (50:50, v/v). The intra-day precision (coefficient of variation) and accuracy for quality control samples ranged from 1.32 to 8.91% and from 92.8 to 108%, respectively. The inter-day precision and accuracy ranged from 2.13 to 8.45% and from 97.0 to 104%, respectively. The analytical method showed excellent sensitivity using a small sample volume (0.1 mL) with a lower limit of quantitation of 5 pg/mL. This method is robust and has been successfully employed in a pharmacokinetic study of Dex in neonates and infants postoperative from cardiac surgery.

Determination of blood dexmedetomidine in dried blood spots by LC-MS/MS to screen therapeutic levels in paediatric patients

Dexmedetomidine is an imidazole derivative, with high affinity for α2 adrenergic receptors, used for sedation, analgesia and adjuvant anaesthesia. In this study, an analytical method for the quantification of dexmedetomidine in dried blood spots was developed, validated and applied. The drug was extracted from dried blood spot by liquid extraction; the separation was carried out by ultra high-resolution liquid chromatography in reverse phase coupled to tandem mass spectrometry method. An X Select cyano 5 μm HSS column (2.1 X 150 mm, Waters) and a mobile phase composed of 0.1% formic acid: acetonitrile [50:50 v/v], were used. The test was linear over the concentration range of 50 to 2000 pg/mL. The coefficients of variation for the intra and interday trials were less than 15%. The drug was stable under the conditions tested. The method was successfully applied for the quantification of 6 patients, aged 0 to 2 years, with classification ASA I, who underwent ambulatory surgeries, receiving a dose of 1 μg/Kg dexmedetomidine IV. The drug concentrations in the different sampling times were in the range of 76 to 868 pg/mL.

An improved liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantification of dexmedetomidine concentrations in samples of human plasma

Dexmedetomidine (DMET) is a sedative, analgesic and anxiolytic with minimum adverse respiratory effects. An LC-MS/MS bioanalytical method has been developed and validated to accurately measure DMET concentrations in samples of human plasma. The method overcomes difficulties in the extraction and quantification of DMET due to the fact that it binds strongly to glass and plastic tubes, as well as solid phase extraction (SPE) cartridges. Human plasma (50 μL) was mixed with the internal standard (IS) (DMET-d4) solution (100 μL) and 0.1% formic acid (50 μL) and extracted using Oasis HLB 1 CC (30 mg) solid phase extraction (SPE) cartridges (Waters^®). The glass tubes were coated with bovine serum albumin (BSA) 0.5% (20 μL) before eluting DMET and the IS. After evaporation under nitrogen at room temperature, the analytes were reconstituted in 20% acetonitrile in 0.1% formic acid in water and transferred to silanized glass vials. An electrospray ionisation (ESI) mass spectrometry method in positive mode was created and the precursor/product transitions (m/z) were 201.1 → 95.0 (DMET) and 204.9 → 99.0 (IS). The method was robust and fully validated based on the 2012 EMEA guideline for bioanalytical method validation in the concentration range of 0.5-20 ng/mL. Using this assay, we showed that DMET binds strongly to Extracorporeal Membrane Oxygenation (ECMO) circuits, consistent with expectations for small lipophilic compounds.

Population Pharmacokinetics of Dexmedetomidine After Short Intravenous Infusion in Chinese Children

BACKGROUND AND OBJECTIVE

Dexmedetomidine is a highly selective alpha2-adrenoceptor agonist with sedative and analgesic properties which is also used in pediatric anesthesia. Although the pharmacokinetics of dexmedetomidine have been studied in pediatric patients, there are no data for Chinese children available. As alterations in pharmacokinetics due to ethnicity cannot be ruled out, it was the aim of this study to characterize the pharmacokinetics of dexmedetomidine in Chinese pediatric patients.

METHODS

Thirty-nine children aged 1-9 years undergoing surgery were enrolled in the study. Dexmedetomidine was administered as short intravenous infusion of 1-2 µg/kg in 10 min. Venous blood samples were drawn until 480 min after stopping of infusion. Dexmedetomidine plasma concentrations were measured with high-performance liquid chromatography and mass spectrometry. Pharmacokinetic modeling was performed by population analysis using linear compartment models.

RESULTS

Data of 36 patients (age 1-9 years, weight 10-27 kg) were analyzed. The pharmacokinetics of dexmedetomidine were best described by a two-compartment model with an allometric power model and estimates standardized to 70 kg body weight. The population estimates (95 % CI) per 70 kg bodyweight were: clearance 36.2 (33.3-41.1) l/h, central volume of distribution 84.3 (70.3-91.4) l, intercompartmental clearance 82.8 (63.6-136.6) l/h, peripheral volume of distribution 114 (95-149) l, and terminal half-life 4.4 (3.6-5.3) h. Age did not show any influence on weight-adjusted parameters.

CONCLUSIONS

Chinese children showed a similar clearance, but larger volumes of distribution and longer terminal half-life when compared to studies in Caucasians.

TRIAL REGISTRATION

ChiCTR-OPC-14005659.

HPLC-MS/MS method for dexmedetomidine quantification with Design of Experiments approach: application to pediatric pharmacokinetic study

AIM

The purpose of this work was to develop and validate a rapid and robust LC-MS/MS method for the determination of dexmedetomidine (DEX) in plasma, suitable for analysis of a large number of samples.

METHOD

Systematic approach, Design of Experiments, was applied to optimize ESI source parameters and to evaluate method robustness, therefore, a rapid, stable and cost-effective assay was developed. The method was validated according to US FDA guidelines. LLOQ was determined at 5 pg/ml. The assay was linear over the examined concentration range (5-2500 pg/ml), Results: Experimental design approach was applied for optimization of ESI source parameters and evaluation of method robustness. The method was validated according to the US FDA guidelines. LLOQ was determined at 5 pg/ml. The assay was linear over the examined concentration range (R² > 0.98). The accuracies, intra- and interday precisions were less than 15%. The stability data confirmed reliable behavior of DEX under tested conditions.

CONCLUSION

Application of Design of Experiments approach allowed for fast and efficient analytical method development and validation as well as for reduced usage of chemicals necessary for regular method optimization. The proposed technique was applied to determination of DEX pharmacokinetics in pediatric patients undergoing long-term sedation in the intensive care unit.

Detection of dexmedetomidine in human breast milk using liquid chromatography-tandem mass spectrometry: Application to a study of drug safety in breastfeeding after Cesarean section

Several analytical methods for dexmedetomidine (DEX) in human plasma have been published, but quantification of DEX in human breast milk has not been described. In this article, we describe a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method suitable for quantification of DEX in human breast milk. DEX and an internal standard were extracted in a single liquid-liquid extraction step with diethyl ether from 200μL of human breast milk. HPLC was performed on a TSK-gel ODS-100V column with isocratic elution at a flow rate of 0.3mL/min using a mobile phase of 5mM ammonium formate:0.1% formic acid in acetonitrile (60:40, v/v). Detection was performed using an API4000 mass spectrometer with positive electrospray ionization. The method was validated in the concentration range of 10pg/mL (lower limit of quantification) to 2000pg/mL. The intra- and inter-day accuracy were within ±5.8% and precision was <6.31% based on the coefficient of variation. The recoveries of DEX in human breast milk were 82.4-87.9%. Recovery and matrix effects were consistent and reproducible for human breast milk. The method is robust and was successfully used in a study of drug safety in breastfeeding in patients after administration of DEX.

Dexmedetomidine added to ropivacaine extends the duration of interscalene brachial plexus blocks for elective shoulder surgery when compared with ropivacaine alone: a single-center, prospective, triple-blind, randomized controlled trial

BACKGROUND AND OBJECTIVES

Research suggests that the addition of dexmedetomidine to local anesthetics can prolong peripheral nerve blocks; however, clinical safety data are limited, and interscalene blocks have not been studied. The present study was designed to test the hypothesis that dexmedetomidine added to ropivacaine would safely enhance the duration of analgesia without adverse effects when compared with ropivacaine alone.

METHODS

We conducted a single-center, prospective, randomized, triple-blind, controlled trial of 62 patients undergoing elective shoulder surgery under general anesthesia with an interscalene block. Patients underwent ultrasound-guided interscalene blocks using either 12 mL of 0.5% ropivacaine or 0.5% ropivacaine plus 150-µg dexmedetomidine. The primary outcomes were self-reported duration of the nerve block and safety assessment (adverse effects and neurological sequelae). Data were analyzed in a blinded fashion.

RESULTS

The median duration of the nerve block was 18 hours (95% confidence interval, 18-20) in the dexmedetomidine group and 14 hours (95% confidence interval, 14-16) in the ropivacaine group (P = 0.0001). Dexmedetomidine also lowered pain scores for the first 14 hours postoperatively and significantly hastened the time to sensory (P = 0.04) and motor (P = 0.002) block onset. Dexmedetomidine lowered heart rate but blood pressures were stable. Plasma levels of ropivacaine were not different between groups, and plasma dexmedetomidine levels were relatively low. There were no adverse events or neurological sequelae.

CONCLUSIONS

Dexmedetomidine added to ropivacaine for interscalene blocks increased the duration of the nerve block and improved postoperative pain. These additional efficacy and safety data should encourage further study of peripheral perineural dexmedetomidine in humans.

A dose-response study of dexmedetomidine administered as the primary sedative in infants following open heart surgery

OBJECTIVE

To evaluate the dose-response relationship of dexmedetomidine in infants with congenital heart disease postoperative from open heart surgery.

DESIGN

Prospective open-label dose-escalation pharmacokinetic-pharmacodynamic study.

SETTING

Tertiary pediatric cardiac ICU.

PATIENTS

Thirty-six evaluable infants, 1-24 months old, postoperative from open heart surgery requiring mechanical ventilation.

INTERVENTIONS

Cohorts of 12 infants were enrolled sequentially to one of the three IV loading doses of dexmedetomidine (0.35, 0.7, and 1 mcg/kg) over 10 minutes followed by respective continuous infusions (0.25, 0.5, and 0.75 mcg/kg/hr) for up to 24 hours.

MEASUREMENTS AND MAIN RESULTS

Dexmedetomidine plasma concentrations were obtained at timed intervals during and following discontinuation of infusion. Pharmacodynamic variables evaluated included sedation scores, supplemental sedation and analgesia medication administration, time to tracheal extubation, respiratory function, and hemodynamic parameters. Infants achieved a deeper sedation measured by the University of Michigan Sedation Scale score (2.6 vs 1) despite requiring minimal supplemental sedation (0 unit doses/hr) and fewer analgesic medications (0.07 vs 0.15 unit doses/hr) while receiving dexmedetomidine compared with the 12-hour follow-up period. Thirty-one patients were successfully extubated while receiving the dexmedetomidine infusion. Only one patient remained intubated due to oversedation during the infusion. While receiving dexmedetomidine, there was a decrease in heart rate compared with baseline, 132 versus 161 bpm, but there was an increase in heart rate compared with postinfusion values, 132 versus 128 bpm. There was no statistically or clinically significant change in mean arterial blood pressure.

CONCLUSIONS

Dexmedetomidine administration in infants following open heart surgery can provide improved sedation with reduction in supplemental medication requirements, leading to successful extubation while receiving a continuous infusion. The postoperative hemodynamic changes that occur in infants postoperative from open heart surgery are multifactorial. Although dexmedetomidine may play a role in decreasing heart rate immediately postoperative, the changes were not clinically significant and did not fall below postinfusion heart rates.

Development of a stable isotope dilution UPLC-MS/MS method for quantification of dexmedetomidine in a small amount of human plasma

Dexmedetomidine (Dex) is a selective central α2-agonist with anesthetic properties and has been used in clinical practice for sedation in the intensive care unit (ICU) after operations. In this study, an analytical assay for the determination of Dex in a small amount of plasma was developed for the application to pediatric ICU trials. The quantification of Dex was constructed using the original stable isotope Dex-d3 for electrospray ionization-tandem mass spectrometry (ESI-MS/MS) in the selected reaction monitoring mode. A rapid ultra-performance liquid chromatography technique was adopted using ESI-MS/MS with a runtime of 3 min. Efficacious concentration levels (50 pg/mL to 5 ng/mL) could be evaluated using a very small amount of plasma (10 μL) from patients. The lower limit of the quantification was 5 pg/mL in the plasma (100 µL). For sample preparation, a solid-phase extraction was used along with the OASIS-HLB cartridge type. Recovery values ranged from 98.8 to 100.3% for the intra- [relative standard deviation (RSD), 0.9-1.3%] and inter- (RSD, 0.9-1.5%) day assays. A stable test had recovery values that ranged from 97.8 to 99.7% with an RSD of 1.0-1.9% for the process/wet extract, bench-top, freeze-thaw and long-term tests. This method was used to measure the Dex levels in plasma from pediatric ICU patients. In the clinical ICU trial, the small amount of blood (approximate plasma volume, 200 μL) remaining from blood gas analysis was reused and targeted for the clinical analysis of Dex in plasma.

In vitro clearance of dexmedetomidine in extracorporeal membrane oxygenation

Dexmedetomidine (DMET) is a useful agent for sedation, both alone and in combination with other agents, in critically ill patients, including those on extracorporeal membrane oxygenation (ECMO) therapy. The drug is a clonidine-like derivative with an 8-fold greater specificity for the alpha 2-receptor while maintaining respiratory and cardiovascular stability. An in vitro ECMO circuit was used to study the effects of both “new” and “old” membrane oxygenators on the clearance of dexmedetomidine over the course of 24 hours. Once primed, the circuit was dosed with 840 μg of dexmedetomidine for a final concentration of 0.9 μg/ml. Serial samples, both pre- and post-oxygenator, were taken at 5, 60, 360, and 1440 minutes. Concentrations of the drug were expressed as a percentage of the original concentration remaining at each time point, both for new and old circuits. The new circuits were run at a standard flow for 24 hours, after which time the circuit was considered old and re-dosed with dexmedetomidine and the trial repeated. Results show that dexmedetomidine losses occur early in the circuits and then continue to decline. Initial losses in the first hour were 11+-65% and 59-73% pre- and post-oxygenator in the new circuit and 36-50% and 42-72% in the old circuit. The clearance of the drug through the membrane oxygenator exhibits no statistical difference between pre and post or new and old circuits. Dexmedetomidine can be expected to exhibit concentration changes during ECMO therapy. This effect appears to be more related to adsorption to the polyvinyl chloride (PVC) tubing rather than the membrane oxygenator. Dosage adjustments during dexmedetomidine administration during ECMO therapy may be warranted in order to maintain adequate serum concentrations and, hence, the desired degree of sedation.*(Lack of equilibrium)

Stability of dexmedetomidine 4 μg/mL in polypropylene syringes

PURPOSE

The results of a study to determine the long-term (up to 14 days) stability of diluted dexmedetomidine kept in polypropylene syringes under typical pharmacy storage conditions are presented.

METHODS

Four samples of dexmedetomidine injection diluted to 4 μg/mL in 0.9% sodium chloride were prepared and divided into 25-mL portions for storage in syringes at ambient room temperature (20-25 °C) with light exposure or under refrigeration (5 °C) in darkness. At 24 and 48 hours, the percentage of the initial dexmedetomidine concentration remaining in all samples was assessed via high-performance liquid chromatography with diode-array detection; further stability testing of the refrigerated samples was performed on days 7 and 14. At each time point, the test samples were visually inspected for color, clarity, and signs of formation of particulate matter.

RESULTS

As determined by chromatographic analyses, the samples of diluted dexmedetomidine stored in syringes at room temperature exhibited a loss of drug concentration of <10% over 48 hours; the refrigerated samples exhibited a loss of drug concentration of <5% over 14 days. All of the syringe-stored samples remained clear and colorless on visual inspection for the duration of the study.

CONCLUSION

Dexmedetomidine diluted to 4 μg/mL in 0.9% sodium chloride injection was stable for at least 48 hours at 20-25 °C and 14 days at 5 °C when stored in polypropylene syringes.

Pharmacokinetics of dexmedetomidine in Chinese post-surgical intensive care unit patients

BACKGROUND

Dexmedetomidine is a rather new drug in China. We sought to describe the pharmacokinetics of dexmedetomidine in patients requiring post-operative sedation and ventilation in our surgical intensive care unit.

METHODS

Twenty-two patients received post-operative infusions of dexmedetomidine at 6 μg/kg/h for 10 min, followed by 0.4 μg/kg/h for 350 min. Venous blood samples were drawn and assayed for plasma concentration. The pharmacokinetics were analysed using a nonlinear mixed-effect model with an interindividual and intraindividual error model. An initial estimation was performed to determine which of the one-, two- or three-compartment models is best to describe the concentration-time data. The covariates age, gender, weight, height, lean body mass (LBM), body surface area (BSA) and body mass index (BMI) were tested for significant effects on parameters using a stepwise forward addition and backward elimination approach. Covariate effects were judged based on changes in the objective function value (OFV).

RESULTS

The pharmacokinetics of dexmedetomidine were best described by a three-compartment model. The model was further improved when height was a covariate of systemic clearance (Cl1), with a decrease in OFV by -13.56 (P<0.01). From the heights of 155-178 cm, Cl1 increased by approximately 143%. The final pharmacokinetic parameter values were as follows: V1 =63.4 l, V2=41.3 l, V3 =284.3 l, Cl1=0.47×(height/160 cm)(6.42) l/min, Cl2=2.43 l/min and Cl3=0.086 l/min.

CONCLUSIONS

This study identified (i) the effect of height on the pharmacokinetics of dexmedetomidine; (ii) that there is no influence of age, gender, weight, LBM, BSA and BMI on pharmacokinetic parameters; and (iii) it established a preliminary population pharmacokinetic model for Chinese patients.

Population pharmacokinetics of dexmedetomidine in infants after open heart surgery

BACKGROUND

Dexmedetomidine is a highly selective alpha(2)-agonist with hypnotic, analgesic, and anxiolytic properties. In adults, it provides sedation while preserving respiratory function facilitating extubation. Only limited pharmacokinetic data are available for pediatric patients. The primary aim of this study was to determine the pharmacokinetics of dexmedetomidine in infants after open heart surgery.

METHODS

We evaluated 36 infants, aged 1 to 24 months, after open heart surgery. Cohorts of 12 infants requiring mechanical ventilation after open heart surgery were enrolled sequentially to 1 of the 3 initial loading dose-continuous IV infusion (CIVI) regimens: 0.35-0.25, 0.7-0.5, or 1-0.75 microg/kg-microg/kg/h. The initial loading dose was administered over 10 minutes immediately postoperatively followed by a CIVI of up to 24 hours. Plasma dexmedetomidine concentrations were determined using a validated high-performance liquid chromatography tandem mass spectrometry assay. A population nonlinear mixed effects modeling approach was used to characterize dexmedetomidine pharmacokinetics.

RESULTS

Pharmacokinetic parameters of dexmedetomidine were estimated using a 2-compartment disposition model with weight on drug clearance, intercompartmental clearance, central and peripheral volume of distributions, total bypass time as a covariate on clearance and central volume of distribution, and age and ventricular physiology as covariates on clearance. Infants demonstrated a clearance of 28.1 mL/min/kg(0.75), intercompartmental clearance of 93.4 mL/min/kg(0.75), central volume of distribution of 1.2 L/kg, and peripheral volume of distribution of 1.5 L/kg.

CONCLUSIONS

Dexmedetomidine clearance increased with weight, age, and single-ventricle physiology, whereas total bypass time was associated with a trend toward decreasing clearance, and central volume of distribution increased as a function of total bypass time. The dependence of clearance on body weight supports current practice of weight-based dexmedetomidine dosing, whereas the clinical impact of the remaining covariate effects requires further investigation. Initial loading doses in the range of 0.35 to 1 microg/kg over 10 minutes and CIVI of 0.25 to 0.75 microg/kg/h were well tolerated in this infant population.

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.