Simultaneous determination of unbound ropivacaine in rat blood and brain using microdialysis

Sample preparation techniques for protein binding measurement in radiopharmaceutical approaches: A short review

Plasma protein binding (PPB) measurement is a key step in radiopharmaceutical studies for the development of positron emission tomography (PET) radioligands. PPB refers to the binding degree of a radioligand, radiotracer, or drug to blood plasma proteins or tissues after administration into the body. Several techniques have been successfully developed and applied for PPB measurement of PET radioligands. However, there is room for progress among these techniques in relation to duration time, adaptability with nonpolar radioligands, in vivo measurement, specificity, and selectivity. This mini review gives a brief overview of advances, limitations, and prospective applications of commercially-available PPB methods.

Pretreatment of plasma samples by a novel hollow fiber centrifugal ultrafiltration technique for the determination of plasma protein binding of three coumarins using acetone as protein binding releasing agent

A novel and practical sample pretreatment method based on hollow fiber centrifugal ultrafiltration (HFCF-UF) was developed to determine plasma protein binding by using HPLC. The samples for analyzing unbound and total concentrations could be prepared in parallel simultaneously by the same device. It only required centrifugation for a short time and the filtrate could be injected directly for HPLC analysis without further treatment. Coumarins were selected as the model drugs. Acetone was chosen as the releasing agent to free the binding drug from the drug-protein complex for the total drug concentration determination. Non-specific bindings (NSBs) between the analytes and hollow fiber membrane materials were investigated. The type and volume of protein binding releaser were optimized. Additionally, centrifugal speed and centrifugal time were considered. Under the optimized conditions, the absolute recovery rates of the unbound and total concentrations were in the range of 97.5-100.9% for the three analytes. The limits of detection were in the range of 0.0135-0.0667μgmL(-1). In vitro plasma protein binding of the three coumarins was determined at three concentrations using the validated method and the relative standard deviations (RSDs) were less than 3.4%. Compared with traditional method, the HFCF-UF method is simple to run, no specialized equipment requirement and is a more accurate plasma pretreatment procedure with almost excellent drug-protein binding equilibrium. Therefore, this method can be applied to determine the plasma protein binding in clinical practice. It also provides a reliable alternative for accurate monitoring of unbound or total drug concentration in therapeutic drug monitoring (TDM).

Simultaneous determination of three local anesthetic drugs from the pipecoloxylidide group in human serum by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous analysis of the local anesthetic amide drugs, bupivacaine, mepivacaine and ropivacaine, belonging to the pipecoloxylidide group using a C(18) reversed-phase column (150 x 4.6 mm I.D.) filled with 5-microm particles and attached to a UV detector. The mobile phase was composed of acetonitrile-methanol-30 mM NaH(2)PO(4) (pH 5.6) (100:100:300, v/v/v) and the flow rate was 1ml/min. The absorbance of the eluate was monitored at 210 nm. The retention times of the three compounds were: 4.6 min (mepivacaine), 9.7min (ropivacaine) and 16.4 min (bupivacaine). With this sample preparation method, good and consistent recoveries of the three compounds were obtained: 88-91% for mepivacaine, 87-89% for ropivacaine and 88-91% for bupivacaine. The limit of quantification for three compounds in human serum was 2 ng/ml for mepivacaine, 5 ng/ml for bupivacaine and ropivacaine. This method may be useful in clinical and forensic applications for the determination or identification of the local anesthetic drugs: bupivacaine, mepivacaine or ropivacaine.

Liquid chromatography–electrospray mass spectrometry determination of free and total concentrations of ropivacaine in human plasma

A specific and sensitive liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for the determination of free and total ropivacaine in human plasma. The work-up procedure involved a simple precipitation of plasma proteins with methanol. Etidocaine served as the internal standard. After microscale equilibrium-dialysis, measurement of free ropivacaine levels was performed after direct injection of the dialysate into the chromatograph. The system used a Zorbax eclipse XD8 C8 analytical column packed with 5 microm diameter particles as the stationary phase. The mobile phase consisted of a 15-min gradient (mobile phase A: 0.05% (v/v) trimethylamine in acetonitrile, mobile phase B: 2mM ammonium formate buffer (pH 3)). Mass spectrometric data were acquired in single ion monitoring mode at m/z 275 for ropivacaine and m/z 277 for etidocaine. The drug/internal standard peak area ratios (plasma) or peak areas (dialysate) were linked via a quadratic relationship to concentrations. Precision ranged from 1 to 7.6% accuracy was between 92.6 and 109%. The lower limits of quantitation were 1 microg/l in plasma and 2 microg/l in the dialysate. This method was found suitable for the analysis of plasma samples collected during a clinical trial performed in 30 infants undergoing epidural anaesthesia or continuous psoas compartment block.

Liquid Chromatographic Determination of Plasma Ropivacaine for Assessing Pharmacokinetics of the Viscous Preparation

We developed assay method for determination of plasma ropivacaine by using reversed-phase high performance liquid chromatography (HPLC) equipped with ordinary octadecylsilyl silica-gel (ODS) column. Plasma samples spiked with internal standard (bupivacaine) were treated by ethylacetate to extract ropivacaine and internal standard. The ropivacaine and internal standard separated on ODS column were detected by an ultra violet (UV) detector set at 215 nm. The mobile phase solvent consisted of acetonitrile, methanol and 0.05 M phosphate buffer adjusted to pH 4.0 (10 : 30 : 60, v/v) was pumped at a flow rate of 0.8 ml/min. The calibration curve of ropivacaine was linear at the concentration of 25-1,000 ng/ml (r=0.9998). The recoveries of ropivacaine from plasma were greater than 87.9% with the coefficient of variations (CVs) less than 6.1%. The CVs for intra- and inter-day assay of ropivacaine were 2.0-12.0% and 1.7-14.8%, respectively. This HPLC method was applied to determining plasma ropivacaine in two healthy subjects after receiving 0.5% ropivacaine viscous preparation, which was prepared in our hospital. Our preliminary pharmacokinetic data showed that ropivacaine viscous could be used safely based on the plasma ropivacaine concentrations (C(max): 89-125 ng/ml) for pain relief in oral mucosa.

Assaying protein unbound drugs using microdialysis techniques

Compared with traditional sampling methods, microdialysis is a technique for protein unbound drug sampling without withdrawal of biological fluids and involving minimal disturbance of physiological function. Conventional total drug sample consists of unbound drugs and protein bound drugs, which are loosely bound to plasma proteins such as albumin and alpha-1 acid glycoprotein, forming an equilibrium ratio between bound and unbound drugs. However, only the unbound fraction of drug is available for absorption, distribution, metabolism and elimination, and delivery to the target sites for pharmacodynamic actions. Although several techniques have been used to determine protein unbound drugs from biological fluids, including ultrafiltration, equilibrium dialysis and microdialysis, only microdialysis allows simultaneous sampling of protein unbound chemicals from plasma, tissues and body fluids such as the bile juice and cerebral spinal fluid for pharmacokinetic and pharmacodynamic studies. This review article describes the technique of microdialysis and its application in pharmacokinetic studies. Furthermore, the advantages and limitations of microdialysis are discussed, including the detailed surgical techniques in animal experiments from rat blood, brain, liver, bile duct and in vitro cell culture for unbound drug analysis.