Agnieszka Bienert

Pharmacokinetics and pharmacodynamics of propofol in patients undergoing abdominal aortic surgery

Available propofol pharmacokinetic protocols for target-controlled infusion (TCI) were obtained from healthy individuals. However, the disposition as well as the response to a given drug may be altered in clinical conditions. The aim of the study was to examine population pharmacokinetics (PK) and pharmacodynamics (PD) of propofol during total intravenous anesthesia (propofol/fentanyl) monitored by bispectral index (BIS) in patients scheduled for abdominal aortic surgery. Population nonlinear mixed-effect modeling was done with Nonmem. Data were obtained from ten male patients. The TCI system (Diprifusor) was used to administer propofol. The BIS index served to monitor the depth of anesthesia. The propofol dosing was adjusted to keep BIS level between 40 and 60. A two-compartment model was used to describe propofol PK. The typical values of the central and peripheral volume of distribution, and the metabolic and inter-compartmental clearance were V(C) = 24.7 l, V(T) = 112 l, Cl = 2.64 l/min and Q = 0.989 l/min. Delay of the anesthetic effect, with respect to plasma concentrations, was described by the effect compartment with the rate constant for the distribution to the effector compartment equal to 0.240 min(-1). The BIS index was linked to the effect site concentrations through a sigmoidal E(max) model with EC(50) = 2.19 mg/l. The body weight, age, blood pressure and gender were not identified as statistically significant covariates for all PK/PD parameters. The population PK/PD model was successfully developed to describe the time course and variability of propofol concentration and BIS index in patients undergoing surgery.

Assessing circadian rhythms during prolonged midazolam infusion in the pediatric intensive care unit (PICU) children

BACKGROUND This study evaluates possible circadian rhythms during prolonged midazolam infusion in 27 pediatric intensive care unit (PICU) children under mechanical ventilation. METHODS Blood samples for midazolam and 1-OH-midazolam assay were collected throughout the infusion at different times of the day. The blood pressure, heart rate and body temperature were recorded every hour for the rhythms analysis. Population nonlinear mixed-effect modeling with NONMEM was used for data analysis. RESULTS A two-compartment model for midazolam pharmacokinetics and a one-compartment model for midazolam metabolite adequately described the data. The 24 h profiles of all monitored physiological parameters were greatly disturbed/abolished in comparison with the well-known 24 h rhythmic patterns in healthy subjects. There was no significant circadian rhythm detected with respect to midazolam pharmacokinetics, its active metabolite pharmacokinetics and all monitored parameters. CONCLUSIONS We concluded that the light-dark cycle did not influence midazolam pharmacokinetics in intensive care units children. Also, endogenous rhythms in critically ill and sedated children are severely disturbed and desynchronized. Our results confirmed that it is necessary to adjust the dose of midazolam to the patients body weight. The low value of midazolam clearances observed in our study was probably caused by mechanical ventilation, which was shown to decrease the cardiac output.

Influence of Time of Day on Propofol Pharmacokinetics and Pharmacodynamics in Rabbits

This study evaluates the administration time-of-day effects on propofol pharmacokinetics and sedative response in rabbits. Nine rabbits were sedated with 5 mg/kg propofol at three local clock times: 10:00, 16:00, and 22:00 h. Each rabbit served as its own control by being given a single infusion at the three different times of day on three separate occasions. Ten arterial blood samples were collected during each clock-time experiment for propofol assay. A two-compartment model was used to describe propofol pharmacokinetics, and the pedal withdrawal reflex was used as the sedation pharmacodynamic response. The categorical data comprising the presence or absence of pedal withdrawal reflex was described by a logistic model. The typical volume of the central compartment equaled 7.67 L and depended on rabbit body weight. The elimination rate constant depended on drug administration time; it was lowest at 10:00 h, highest at 16:00 h, and intermediate at 22:00 h. Delay of the anesthetic effect, with respect to plasma concentrations, was described by the effect compartment, with the rate constant for the distribution to the effector compartment equal to 0.335 min−1. Drug concentration had a large effect on the probability of anesthesia. The degree of anesthesia was largest at 10:00 h, lowest at 16:00 h, and intermediate at 22:00 h. In summary, both the pharmacokinetics and pharmacodynamics of propofol in rabbits depended on administration time. The developed population approach may be used to assess chronopharmacokinetics and chronopharmacodynamics of medications in animals and humans. (Author correspondence: agnbienert@op.pl)

Influence of demographic factors, basic blood test parameters and opioid type on propofol pharmacokinetics and pharmacodynamics in ASA I-III patients.

The aim of the study was to examine population pharmacokinetics (PK) and pharmacodynamics (PD) of propofol (CAS 2078-54-8) during total intravenous anesthesia monitored by spectral frequency index (SFx). Twenty-eight patients of ASA physical status I-III (ASA: American Society of Anesthesiologists) scheduled for laparoscopic cholecystectomy were included. In group I an anesthesia was induced with a bolus of propofol (2 mg/kg) and remifentanil (CAS 132875-61-7) (1.0 microg/kg), followed by a continuous infusion of remifentanil. In group II, an alfentanil (CAS 71195-58-9) (10 microg/kg) bolus dose was followed by a continuous infusion of alfentanil. The general anesthetic technique included propofol, opioid and muscle relaxant. During anesthesia, the propofol infusion rate (3-8 mg/kg/h) was adjusted to the SFx value. Venous blood samples were collected from the patients during 240 min after termination of the infusion. A two compartment model was used to describe propofol PK. A standard effect compartment model was used to describe the delay between the effect and the concentration of propofol. The SFx index was linked to the effect site concentrations through a sigmoidal Emax model. The influence of continuous (body weight, age, blood pressure, heart rate and blood oxygenation, serum protein, the erythrocyte count, hemoglobin and hematocrit, serum creatinine and creatinine clearance) and categorical (gender and the type of opioid) covariates on the pharmacokinetic and pharmacodynamic parameters was investigated. PK/PD analysis was performed using NONMEM. All the screened covariates did not influence propofol PK and PD, except of the opioid type. The central compartment volume of propofol was larger in the presence of remifentanil than in the presence of alfentanil.

Pharmacokinetics of sufentanil during long‐term infusion in critically ill pediatric patients

The aim of this study was to develop a population pharmacokinetic model of sufentanil and to assess the influence of covariates in critically ill children admitted to a pediatric intensive care unit. After institutional approval, 41 children were enrolled in the study. Blood samples for pharmacokinetic (PK) assessment were collected from routinely placed arterial catheters during and after discontinuation of infusion. Population nonlinear mixed‐effects modeling was performed using NONMEM. A 2‐compartment model described sufentanil PK sufficiently. Typical values of the central and peripheral volume of distribution and the metabolic and intercompartmental clearance for a theoretical patient weighing 70 kg were VC = 7.90 l, VT = 481 L, Cl = 45.3 L/h, and Q = 38.3 L/h, respectively. High interindividual variability of all PK parameters was noted. Allometric/isometric principles to scale sufentanil PK revealed that to achieve the same steady‐state sufentanil concentrations in plasma for pediatric patients of different body weights, the infusion rate should follow the formula (infusion rate for a 70‐kg adult patient, μg/h) × (body weight/70 kg)0.75. Severity of illness described by PRISM score, the monitored physiological and laboratory parameters, and coadministered drugs such as vasopressors were not found to be significant covariates.

Analysis of the gene polymorphism of aldosterone synthase (CYP11B2) and atrial natriuretic peptide (ANP) in women with preeclampsia

OBJECTIVE Preeclampsia (PE) is a major cause of mortality of mothers, fetuses and newborns around the world. The etiology of preeclampsia has not yet been clarified, but many studies indicate a multifactorial basis of PE. Aldosterone synthase (CYP11B2) is responsible for synthesis of aldosterone responsible for regulating blood pressure. Similarly, natriuretic peptide (ANP) regulates blood pressure through a variety of mechanisms affecting the sodium concentration and the amount of extracellular fluid. Currently, attention is paid to the role of the polymorphisms in the expression level of these genes. The aim of the study was to determine the frequencies of genotypes and alleles for polymorphisms of -344C>T CYP11B2 gene and 2238T>C ANP gene in women with preeclampsia and healthy pregnant women from the Caucasian population. STUDY DESIGN The study included a group of 165 pregnant women (59 women with preeclampsia and 109 healthy pregnant women). DNA was extracted from peripheral blood. Determination of the polymorphism of -344C>T CYP11B2 gene and 2238T>C ANP gene was performed by PCR-RFLP method. RESULTS The results showed that the frequencies of the TC and CC genotypes of 2238T>C polymorphism in ANP gene were significantly higher in patients with PE compared to control group. For -344C>T polymorphism of CYP11B2 gene, the frequency of TT genotype was significantly higher in patients with hypertension than in controls (32.2% vs. 23.58%). CONCLUSIONS Our findings showed that gene polymorphism of CYP11B2 (-344C>T) and ANP (2238T>C) may be associated with developing PE during pregnancy.

Do we really know the pharmacodynamics of anaesthetics used in newborns, infants and children? A review of the experimental and clinical data on neurodegeneration.

The practices of anaesthesiology and intensive therapy are difficult to imagine without sedation or general anaesthesia, regardless of whether the patient is a newborn, baby, child or adult. The relevant concerns for children are distinct from those for adults, primarily due to the effects of anatomical, physiological and pharmacokinetic-pharmacodynamic (PK/PD) differences, which become increasingly important in the brains of children as they develop. The process of central nervous system maturation in humans lasts for years, but its greatest activity (myelination and synaptogenesis) occurs during the fetal period and the first two years of life. Many experimental studies have demonstrated that exposure to anaesthetic drugs during this period can induce neurodegenerative changes in the central nervous systems of animals. The extrapolation of these results directly to humans must be performed with great caution, but anaesthesiologists around the world must begin to debate the safety of general anaesthesia in humans. Prospective trials should continue being carried out, and anaesthesia and surgery, delayed if possible among the smallest patients. The simultaneous use of different anaesthetics with the same potential neurotoxicities should also be avoided, potentially in favour of regional anaesthesia techniques, in this group of patients.

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.

The Pharmacokinetics of Propofol in ICU Patients Undergoing Long‐Term Sedation

The aim of this study was to characterize the pharmacokinetics (PK) of propofol in ICU patients undergoing long‐term sedation and to assess the influence of routinely collected covariates on the PK parameters. Propofol concentration–time profiles were collected from 29 patients. Non‐linear mixed‐effects modelling in NONMEM 7.2 was used to analyse the observed data. The propofol pharmacokinetics was best described with a three‐compartment disposition model. Non‐parametric bootstrap and a visual predictive check were used to evaluate the adequacy of the developed model to describe the observations. The typical value of the propofol clearance (1.46 l/min) approximated the hepatic blood flow. The volume of distribution at steady state was high and was equal to 955.1 l, which is consistent with other studies involving propofol in ICU patients. There was no statistically significant covariate relationship between PK parameters and opioid type, SOFA score on the day of admission, APACHE II, predicted death rate, reason for ICU admission (sepsis, trauma or surgery), gender, body weight, age, infusion duration and C‐reactive protein concentration. The population PK model was developed successfully to describe the time‐course of propofol concentration in ICU patients undergoing prolonged sedation. Despite a very heterogeneous group of patients, consistent PK profiles were observed. Copyright

Pharmacokinetics and pharmacodynamics of propofol in children undergoing different types of surgeries

BACKGROUND Propofol is a commonly used agent in total intravenous anesthesia (TIVA). However, the link between its pharmacokinetics and pharmacodynamics has not been fully characterized in children yet. Our aim was to determine the quantitative relationship between the venous plasma concentration and bispectral index (BIS) effect in a heterogeneous group of pediatric patients undergoing various surgical procedures (ASA status I-III). METHODS Nine male and nine female patients were anesthetized with propofol-fentanyl TIVA. Sparse venous samples for propofol concentrations assay and dense BIS measurements were collected during and after the end of infusion. Nonlinear mixed-effect modeling in NONMEM was used for data analysis. RESULTS A three-compartment model was linked with a classical Emax model through a biophase compartment to describe the available data. All clearance and volume terms were allometrically scaled to account for the body mass difference among the patients under study. A typical patient had their PK parameters observed within the range of literature values for children. The pharmacodynamic parameters were highly variable. The EC50 of 2.80 mg/L and the biophase distribution rate constant of 3.33 min(-1) were found for a typical patient. CONCLUSIONS The BIS values in children are highly correlated with the propofol effect compartment concentrations according to the classical Emax concentration-response relationship. Children had slightly lower sensitivity to propofol and slightly higher clearance, as compared with the adult data available in literature. The intra-patient variations in the BIS require the anesthesiologists attention in using BIS values alone to evaluate the depth of anesthesia in children.