High-performance liquid chromatographic method for an automated determination of local anaesthetics in human plasma

Integration of Solid-Phase Extraction and Reversed-Phase Chromatography in Single Protein-Coated Columns for Direct Injection of Bupivacaine in Human Serum

A rapid, reliable and precise integrated solid-phase extraction (SPE) and reversed-phase liquid chromatography method was developed and validated to determine bupivacaine in human serum using single protein-coated analytical columns. The protein-coated columns were packed with four different sorbents: TSK-ODS, LiChrosorb RP-8, LiChrosorb RP-2 and μ-Bondapak CN-bonded silica. The method involved direct injection of serum sample onto the columns for trapping of the analyte, clean-up from weakly retained serum endogenous components, as well as the final separation. The protein-coated columns operated in two different chromatographic modes. Serum proteins were extracted and cleaned up by SPE, whereas the final separation of bupivacaine was based on reversed-phase chromatography. The protein-coated TSK-ODS column resulted in more accurate peak integration and more reproducible results. A linear relationship between the concentrations of drug and peak areas was confirmed in the range of 100-2000 ng/mL. Detection and quantification limits were 24.85 and 85.36 ng/mL, respectively. The average recovery for bupivacaine ranged from 96.48% to 98.81%. The present methodology was successfully applied, with a high degree of confidence, to analyze clinical samples obtained from patient receiving 0.5% bupivacaine therapy.

Bupivacaine concentrations in the lumbar cerebrospinal fluid of patients during spinal anaesthesia

BACKGROUND

Data on bupivacaine concentrations in the cerebral spinal fluid (CSF) during spinal anaesthesia are scarce. The purpose of this study was to determine the concentration of bupivacaine in the lumbar CSF of patients with an adequate level of spinal anaesthesia after injection of plain bupivacaine 0.5%.

METHODS

Sixty patients with an adequate level of spinal block after standardized administration of plain bupivacaine 20 mg in men and of 17.5 mg in women were studied. To measure the CSF bupivacaine concentration, we performed a second lumbar spinal puncture and obtained a CSF sample at a randomized time point 5-45 min after the bupivacaine injection. In addition, we calculated the half-life of bupivacaine in the CSF and tested the hypothesis that the level of spinal block is related to the lumbar CSF bupivacaine concentration.

RESULTS

Men and women had CSF bupivacaine concentrations ranging from 95.4 to 773.0 microg ml(-1) (median 242.4 microg ml(-1)) and from 25.9 to 781.0 microg ml(-1) (median 187.6 microg ml(-1)), respectively. The large variability of bupivacaine concentrations obtained at similar times after subarachnoid administration made calculation of a meaningful half-life of bupivacaine in CSF impossible. There was no association between CSF bupivacaine concentration and spinal block level, and CSF bupivacaine concentrations for the same spinal block level differed between patients by six-fold.

CONCLUSIONS

There is a large variability of CSF bupivacaine concentrations in patients with an adequate level of spinal anaesthesia.

Application of a column selection system and DryLab software for high-performance liquid chromatography method development

This paper describes a strategy for the development of chromatographic methods for drug candidates based upon the use of simple MS compatible mobile phases and optimization of the chromatographic selectivity through variations of the stationary phase and mobile phase pH. The strategy employs an automated column selection system and a series of HPLC columns, varying in hydrophobicity and silanol activity, in combination with DryLab software to develop chromatographic methods for the separation of mixtures of bupivacaine and its metabolites; acidic, basic, and neutral compounds; and atenolol, nitrendipine, and their degradation products.

Separation and determination of bupivacaine in plasma by capillary electrophoresis with tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence detection

A new, rapid, selective and sensitive method is described for determination of bupivacaine by capillary electrophoresis coupled with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)2+] electrochemiluminescence detection. The influence of parameters such as detection potential, Ru(bpy)(3)2+ concentration, buffer concentration and pH, injection time and separation voltage on separation efficiency and ECL peak intensity was systematically investigated. Under optimized conditions, the calibration curve was linear in the range 0.02-10 microg/mL. The RSD was 4.0% (n = 6). The detection limit was 3 ng/mL. The recoveries obtained were about 90%. This method was tested in the analysis of plasma samples taken from a rat after it had received bupivacaine injections.

Determination of bupivacaine and metabolites in rat urine using capillary electrophoresis with mass spectrometric detection

A method using capillary electrophoresis-mass spectrometry (CE-MS) was developed for the structural elucidation of bupivacaine and metabolites in rat urine. Prior to CE-MS analysis, solid-phase extraction (SPE) was used for sample cleanup and preconcentration purposes. Exact mass and tandem mass spectrometric (MS/MS) experiments were performed to obtain structural information about the unknown metabolites. Two instruments with different mass analyzers were used for mass spectrometric detection. A quadrupole time-of-flight (Q-TOF) and a magnetic sector hybrid instrument were coupled to CE and used for the analysis of urine extracts. Hydroxybupivacaine as well as five other isomerically different metabolites were detected including methoxylated bupivacaine.

Effect of non-hypotensive haemorrhage on plasma catecholamine levels and cardiovascular variability in man

BACKGROUND

It is well known from animal research that non-hypotensive haemorrhage produces sympathoexcitatory responses assessable by both the rise in plasma catecholamine levels and the shift of autonomic influences on the heart to more sympathetic and less parasympathetic control. Data in humans are restricted.

METHODS

Heart rate variability (HRV), systolic blood pressure (FINAPRES) variability (BPV), and catecholamine plasma levels were measured before and after haemorrhage in 30 healthy blood donors and compared with those from 10 control subjects without blood loss. Spectral power of HRV and BPV in very low (0.02-0.06 Hz), low (0.07-0.14 Hz), and high (0.15-0.40 Hz) frequency bands were calculated by Fourier analysis. Catecholamine plasma levels were assayed by dual column reverse-phased high-performance liquid chromatography (HPLC).

RESULTS

Haemorrhage of 5.6 +/- 1.2 ml kg-1 body weight increased plasma norepinephrine levels (215 +/- 92 pg ml-1 versus 254 +/- 95 pg ml-1; P = 0.002), increased BPV in the low frequency band (Mayer waves; 1.8 +/- 1.0 ln [mmHg(2)] versus 2.0 +/- 0.9 ln [mmHg(2)]; P = 0.021), and decreased the vagally transmitted high frequency HRV (6.9 +/- 1.1 ln [MI(2)] versus 6.5+/-1.2 ln [MI(2)]; P<0.0001), but did not induce significant changes in heart rate (66 +/- 11 bpm versus 67 +/- 11 bpm; P = 0.79) and arterial blood pressure (mean values: 84 +/- 13 mmHg versus 87 +/- 13 mmHg; P = 0.12).

CONCLUSIONS

As suggested by plasma norepinephrine levels, systolic BPV and HRV, non-hypotensive haemorrhage produces sympathoexcitatory responses as well as vagal withdrawal of heart rate control in humans.

Spectrophotometric determination of etidocaine in pharmaceutical (dental) formulation

A spectrophotometric method was developed for the determination of etidocaine hydrochloride (EH) in injectable pharmaceutical preparation. The proposal of this work was to develop a rapid, simple, inexpensive, precise and accurate visible spectrophotometric method. The method is based on the formation of the ion-pair complex by the EH reaction with bromocresol green in the pH 4.6 which after chloroform extraction gives a yellow color that in basic medium change to blue color and exhibits a maximum absorbance at 625 nm. The calibration graph was linear over the range 2.0-6.0 microg ml(-1) EH calculated on the final yellow solution. The R.S.D. of the slope of the four lines was 0.73%. This method can be applied to injectable pharmaceutical preparation dosage studied.

Automating solid-phase extraction: current aspects and future prospects

This paper reviews current trends and techniques in automated solid-phase extraction. The area has shown a dramatic growth the number of manuscripts published over the last 10 years, including applications in environmental science, food science, clinical chemistry, pharmaceutical bioanalysis, forensics, analytical biochemistry and organic synthesis. This dramatic increase of more that 100% per year can be attributed to the commercial availability of higher throughput 96-well workstations and extraction plates that allow numerous samples to be processed simultaneously. These so-called parallel-processing workstations represent the highest throughput systems currently available. The advantages and limitations of other types of systems, including discrete column systems and on-line solid-phase extraction are also discussed. Discussions of how automated solid-phase extractions can be developed, generic approaches to automated solid-phase extraction, and three noteworthy examples of automated extractions are given. The last part of the review suggests possible near- and long-term directions of automated solid-phase extraction.