Response surface analysis of sevoflurane-remifentanil interactions on consciousness during anesthesia / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Recently, the combination of sevoflurane and remifentanil has been widely used in general anesthesia. In this study, we investigated the sevoflurane-remifentanil pharmacodynamic interactions at clinical concentrations using the observer's assessment of alertness/sedation (OAA/S) and the bispectral index (BIS) by response surface analysis.</p><p><b>METHODS</b>Totally 65 American Society of Anesthesiologists (ASA) I patients age 20 to 50 years old were included in this study. Patients were randomly assigned to be anesthetized with different target end-tidal sevoflurane concentrations that ranged from 0.2% to 3.4% in increments of 0.2%. The end-tidal sevoflurane concentration was maintained constant throughout the study. Remifentanil was infused with a target controlled infusion (TCI) system at increasing step-wise concentrations from 1 ng/ml to 10 ng/ml. The values of OAA/S and BIS at different sevoflurane-remifentanil concentration combinations were measured. The pharmacodynamic interactions between sevoflurane and remifentanil were analyzed by a response surface method. The three-dimensional response surfaces were constructed with Minitab Software. Model parameters were estimated with NONMEM program.</p><p><b>RESULTS</b>Sevoflurane and remifentanil acted synergistically on OAA/S. Sevoflurane alone could produce OAA/S ≤ 1 at a minimal alveolar concentration (MAC) of 0.93%. When used in combination with remifentanil at 1, 3, 6, and 10 ng/ml, the corresponding sevoflurane MACs were reduced to 0.79%, 0.58%, 0.48%, and 0.38%, with reductions of 17.2%, 37.6%, 48.4%, and 62.0% from baseline, respectively. In patients administered remifentanil alone, the OAA/S score was ≥ 3 even when the remifentanil concentration reached 10 ng/ml. BIS was closely associated with the sevoflurane concentration and the remifentanil concentration did not noticeably influence the relationship between the sevoflurane concentration and BIS. A sevoflurane concentration of (1.04 ± 0.19)% to (1.81 ± 0.21)% could maintain a BIS between 60 and 40.</p><p><b>CONCLUSIONS</b>The response surface method can analyze the pharmacodynamic interactions between remifentanil and sevoflurane qualitatively and quantitatively. Within the range of our study (remifentanil ≤ 10 ng/ml, sevoflurane ≤ 3.4%), the two drugs produced synergistic effects on OAA/S but had no interactive effect on BIS. A guideline of BIS between 40 and 60 may cause excessive anesthesia when opioids are used to maintain anesthesia.</p>

The therapeutic drug monitoring network server of tacrolimus for Chinese renal transplant patients / 药学学报

This study is to develop a therapeutic drug monitoring (TDM) network server of tacrolimus for Chinese renal transplant patients, which can facilitate doctor to manage patients' information and provide three levels of predictions. Database management system MySQL was employed to build and manage the database of patients and doctors' information, and hypertext mark-up language (HTML) and Java server pages (JSP) technology were employed to construct network server for database management. Based on the population pharmacokinetic model of tacrolimus for Chinese renal transplant patients, above program languages were used to construct the population prediction and subpopulation prediction modules. Based on Bayesian principle and maximization of the posterior probability function, an objective function was established, and minimized by an optimization algorithm to estimate patient's individual pharmacokinetic parameters. It is proved that the network server has the basic functions for database management and three levels of prediction to aid doctor to optimize the regimen of tacrolimus for Chinese renal transplant patients.

Population pharmacokinetics of rocuronium delivered by target-controlled infusion in adult patients / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Target-controlled infusion (TCI) has been recently developed and successfully implemented in clinical practice. The current study was to estimate the population pharmacokinetics of rocuronium TCI in adult patients using nonlinear mixed-effects model (NONMEM), and to investigate the influence of relevant factors in adult patients.</p><p><b>METHODS</b>Fourteen ASA I-II patients undergoing elective laparoscopy operation with general anesthesia were included. After induction, all patients received rocuronium by TCI system. The beginning target plasma concentration (Cpt) was 2.0 µg/ml, then increased Cpt according to the neuromuscular transmission monitoring. The endpoint of Cpt was determined when the T₁ scale was blocked by 90% - 95%. TCI rocuronium was stopped 30 minutes before the end of the operation. Arterial blood was drawn before anesthesia at 0, 2, 4, 6, 8, 10, 15, 20, 30, 45, 60, 120, 180, 240 and 360 minutes after the infusion of rocuronium was stopped for the analysis of plasma concentrations of rocuronium by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The population pharmacokinetics analysis was performed using NONMEM program.</p><p><b>RESULTS</b>The pharmacokinetics of TCI rocuronium in adult patients was best described by a three-compartment model. Pharmacokinetic parameters were clearance (CL)₁ = 0.205 L/min, CL₂ = 0.324 L/min, CL₃ = 0.0292 L/min, volumes of distribution (V)₁ = 4.00 L, V₂ = 2.28 L, V₃ = 4.26 L, Vdss = 10.54 L. Both age and weight as covariates affected the pharmacokinetic parameters. V₁ and CL₁ were negatively correlated with patient age. CL₁ was positively correlated with weight.</p><p><b>CONCLUSIONS</b>No pharmacokinetic change was noted when rocuronium was administered via TCI. Both age and weight as covariates affected the pharmacokinetic parameters.</p>

Population pharmacokinetics of remifentanil in patients undergoing orthotopic liver transplantation / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Little is known about the influence of liver transplantation on the pharmacokinetics of most anesthetic drugs. The goal of this study was to study the population pharmacokinetics of remifentanil in the different phases of orthotopic liver transplantation (OLT) and the influence of relevant factors.</p><p><b>METHODS</b>Thirteen adult patients undergoing OLT were enrolled. A single bolus infusion of remifentanil 5 microg/kg was administered during the preanhepatic, anhepatic and neohepatic phases of OLT. Arterial blood samples of 1.5 ml were collected at 0 (baseline), 1, 2, 3, 5, 7, 10, 15, 20, 25, 30, 45, 60 and 90 minutes after drug administration. Remifentanil concentration was assayed by high-performance liquid chromatography/mass spectrometry/mass spectrometry (HPLC/MS/MS). Population pharmacokinetic modeling was performed using nonlinear mixed-effects modeling (NONMEM).</p><p><b>RESULTS</b>The pharmacokinetics of remifentanil in patients undergoing OLT was best described by a two-compartment open model. The pharmacokinetic parameters were not influenced by age, gender, operative phase, blood temperature, rehydration volume, or blood loss volume during sampling. The volume of distribution in the central compartment (V(1)) and the volume of distribution in the peripheral compartment (V(2)) were influenced by body weight.</p><p><b>CONCLUSIONS</b>The population pharmacokinetics of remifentanil in patients undergoing OLT can be well described by a two-compartment open model. The functional status of the liver does not significantly affect the pharmacokinetics of remifentanil, but the body weight is an influential factor of V(1) and V(2).</p>

Progress in the study of response surface modeling in investigation of drug-drug interaction in anesthetic drugs / 药学学报

As a novel and effective approach, response surface model is used in the study of drug-drug interactions. When two drugs are used simultaneously, this model can be applied to estimate the key characters of the response surface, to find the desired response region by optimal drugs combination, to explore the mechanism of drug-drug interactions, and thus to guide sound clinical application and reduce the risk and cost. In this article, the model's basic mathematical and pharmacological concepts are introduced, and its research progresses are reviewed.

Population pharmacokinetics of tacrolimus in Chinese renal transplant patients / 药学学报

The goal of this study is to investigate the population pharmacokinetics of oral tacrolimus in Chinese renal transplant patients and to identify possible relationship between covariates and population parameters. Details of drug dosage history, sampling time and concentration of 802 data points in 58 patients were collected retrospectively. Before analysis, the 58 patients were randomly allocated to either the model building group (n=41) or the validation group (n=17). Population pharmacokinetic data analysis was performed using the nonlinear mixed-effects model (NONMEM) program on the model building group. The pharmacokinetics of tacrolimus was best described by a one compartment model with first-order absorption and elimination. Typical values of apparent clearance (CL/F), apparent volume of distribution (V/F) were estimated. A number of covariates including demographic index, clinical index and coadministration of other drugs were evaluated statistically for their influence on these parameters. The final population model related clearance with POD (post operative days), HCT (haematocrit), AST (aspartate aminotransferase) and coadministration of nicardipine and diltiazem. Predictive performance of the final model evaluated with the validation group showed insignificant bias between observed and model predicted concentrations. Typical value of CL/F and V/F was 21.7 L x h(-1) and 241 L, inter-patient variability (RSD) in CL/F and V/F was 41.6% and 49.7%, respectively. The residual variability (SD) between observed and model-predicted concentrations was 2.19 microg x L(-1). The population pharmacokinetic model of tacrolimus in Chinese renal transplant patients was established and significant covariates on the tacrolimus model were identified.