Steven H. Y. Wong

Common effects of touch and vision on postural parameters

Abstract Subjects stood upright with the index finger of the right hand either touching a nearby surface gently or not touching it at all and with the eyes either open or closed. Trajectories of the center of pressure (COP) were analyzed as fractional Brownian motion. The extracted parameters were the effective diffusion (D) coefficients and Hurst (H) exponents for short-term time intervals (corresponding to positively correlated random walks) and long-term time intervals (corresponding to negatively correlated random walks). Gentle tactile contact reduced the effective stochastic activity measured by D to the same extent as the availability of vision. Further, touch interacted with time interval in the same way as vision, with the correlated activity closer to H = 0.5 at both time scales when the finger contacted the nearby surface. The results corroborate and extend major features of recent investigations of haptic influences on posture and recent analyses of vision’s influence on the fractional Brownian motions of the COP. Discussion focused on (a) the equivalence of expropriospecific information (about the body’s orientation to the environment) registered haptically and visually and (b) the possibility that postural sway may reflect exploratory motions in the short term (obtaining information about the postural system) and performatory motions in the long term (using this information).

Determination of fluoxetine and norfluoxetine by high-performance liquid chromatography

A high-performance liquid chromatographic assay was developed for a recently introduced atypical antidepressant, fluoxetine and its demethylated metabolite, norfluoxetine. Prior to analysis, aliquots of alkalinized plasma were extracted with n-hexane and isoamyl alcohol, followed by back-extraction with diluted phosphoric acid. These extracts were injected into a 10 microns, reversed-phase C18 column with phosphate and acetonitrile as the mobile phase and detection at 214 nm. Peak height ratios were linearly correlated up to 800 micrograms/l. Acceptable coefficients of variation were demonstrated for both within-run and day-to-day studies. Selected drugs were checked for interference. The assay was used to monitor nine patients receiving 20 to 80 mg of fluoxetine per day. Plasma concentrations of fluoxetine and norfluoxetine ranged from 37 to 301 micrograms/l and 29 to 326 micrograms/l respectively.

Detection of lipid peroxidation in lung and in bronchoalveolar lavage cells and fluid.

Inhalation of toxic materials such as asbestos, silica, 100% oxygen, ozone, or nitrogen dioxide may lead to an increased production of reactive oxygen metabolites which may initiate lipid peroxidation. Measurement of lipid peroxidation in cells and fluid obtained by bronchoalveolar lavage (BAL), as well as in lung tissue, may aid in monitoring the development and extent of pulmonary damage after inhalation of a toxic substance. In this study, we employed a sensitive assay for detection of malondialdehyde (MDA), a breakdown product of lipid peroxidation. By separation of the adduct with thiobarbituric acid, using a reverse phase high pressure liquid chromatographic technique, we accurately and sensitively measured the content of MDA in BAL cells, lavage fluid, and lavaged lung tissue homogenates of rats. The amounts of sample required for detection of MDA were small enough possibly to be applied to use with human specimens; in addition, recovery of added MDA was acceptable with all types of samples. Inclusion of a metal chelator in the preparation of samples appeared necessary to prevent metal-catalyzed propagation of lipid peroxidation during the assay. Overall, the method described here using samples from rats may be applicable to detecting lipid peroxidation in BAL samples from humans.

Shielded Hydrophobic Phase for Direct Sample Analysis: Preliminary Study for the Analysis of Phenobarbital for Potential Neonatal and Pediatric Drug Monitoring

Abstract Shielded Hydrophobic Phase(SHP) for Direct Sample Analysis of phenobarbital in serum was investigated for Therapeutic Drug Monitoring by studying the column stability and utilization parameters, and by comparison to the established fluorescence polarization immunoassays. This novel packing consisted of 5 um spherical silica particles with 100 A pores, bonded with polar and non-polar functionalities to the inside and outside of the particles. Proteins may be eluted, unretained with solvent front peaks while the drug/metabolites would undergo hydrophobic interaction, eluting later. For Direct Sample Analysis of phenobarbital in serum, 10 uL aliquots, after centrifuged at 9,500 × g for 20 minutes, were injected into the SHP guard column and column, and eluted with phosphate/ACN(9:1). Phenobarbital eluted with k′ of 3.4 at 3.8 minutes. Calibration was linear between 5 to 80 mg/L. Precision studies showed acceptable within-run and day-to-day coefficients of variation. Comparison with FPIA showed accep...

Determination of a Trazadone Metabolite, 1-m-Chlorophenyl- Piperazine in Plasma by Liquid Chromatography

Abstract A liquid chromatographic assay was developed for monitoring a trazodone metabolite, 1-m-chlorophenylpiperazine (mCPP) in plasma. Alkalinzed plasma was extracted with methylene chloride/isoamyl alcohol (98:2), and back-extracted with diluted phosphoric acid. The extracts were analyzed by a high carbon load, 20%, C-18, 5 um column with a ternary mobile phase at 45[ddot]C and detection at 254 nm. Retention volumes of mCPP, the internal standard and trazodone were 22.7, 38.0 and 58.7 ml, respectively. A peak, X, eluded closely with mCPP. Peak height ratios of mCPP/internal standard were linearly correlated to mCPP plasma concentrations between 10 to 100 ug/L. Detection limit was 5 ng and recovery was about 50%. Precision studies showed the within-run and day-to-day coefficients of variation were 4.0 and 5.7%, respectively. Patient samples (n = 6) showed substantial amounts of trazodone but only trace amounts of mCPP.

Supercritical Fluid Chromatography for Therapeutic Drug Monitoring and Toxicology: Methodological Considerations for Open Capillary Tubular Column for the Analysis of Phenobarbital in Serum

Abstract Methodological considerations are presented here for the application of SFC for clinical drug analysis using an open-tubular capillary column with polymethylsiloxane as the stationary phase. Preliminary studies of analysis of phenobarbital in serum showed that the use of liquid-liquid extractions, and recently introduced microfilters did not prevent rapid deterioration of column performance. Through systematic studies with solid-phase, C-18 extraction columns, a retention gap and a non-polar mixture of n-pentane/methylene chloride(25:75) for reconstituting the extracts, the feasibility was established. As a result of the lack of chromatographic interferences as shown by analysis of extract of drug-free serum, the procedure was used to estimate a patients phenobarbital concentration of about 20 mg/L, comparable to a clinically established determination by fluorescence polarization immunoassay. Precision studies showed comparable mean concentrations for the measurement of quality control samples, ...

Advances in chromatography for clinical drug analysis: supercritical fluid chromatography, capillary electrophoresis, and selected high-performance liquid chromatography techniques.

Advances have been made in chromatography complement immunoassay for clinical drug analysis. Chromatographic theory shows that the minimum detectable mass is directly proportional to the square of column radius. Small internal diameter columns are capable of analyzing lower analyte concentrations, and high resolution is achievable in open capillary columns, concomitant with greatly reduced mobile phase consumption and waste. This review, based on the authors experience and literature, focuses on supercritical fluid chromatography (SFC), capillary electrophoresis (CE), and selected high-performance liquid chromatography (HPLC) methodologies— microbore and direct-sample analysis (DSA) using commercially available Restricted Access Media (RAM) and REMEDi. In investigating the feasibility of SFC, the “normal-phase-like” selectivity of carbon dioxide Vas established, affecting the design of the extraction protocol and the elution order of drugs and metabolites. For example, the “more polar” tautomer eluted after FK-506, opposite to the order in the reversed-phase HPLC analysis. CE was investigated by Shihabi et al. for the analysis of pentobarbital and iohexol, while Evenson and Wiktorowicz performed preliminary evaluation of several therapeutic drug monitoring (TDM) drug groups. Innovation in HPLC column technology and hardware have greatly enhanced clinical drug analysis. Microbore“ column, offering enhanced mass sensitivity and high resolution, utilizes small sample size of 5 μl of serum for the analysis of chloramphenicol. Commercially available RAM include internal surface reversed phase, shielded hydrophobic phase, and dual zone media, readily applicable for serum drug analysis without any sample preparation. Recently, an automated HPLC REMEDi offers urine and serum drug screening for toxicology.

Comparison of the serum barbiturate fluorescence polarization immunoassay by the COBAS INTEGRA to a GC/MS method.

The authors evaluated a new Cassette Serum Barbiturates fluorescence polarization immunoassay (FPIA) on the COBAS INTEGRA. The assay was calibrated with secobarbital standards at 0, 0.5, and 4.0 microg/mL. The assay range was 0.030 to 80 microg/mL using an automatic 1/20 postdilution feature. Precision was established for two COBAS INTEGRA instruments for ten days by assaying secobarbital target concentrations ranging from 0.125 to 2.2 microg/mL. The coefficients of variation (CV) for the above target concentrations for the first instrument ranged from 2.7% to 8.3%, and for a second instrument, 3.8 to 8.3%. Seven clinically elevated bilirubin samples were spiked with 0.46 and 1.77 microg/mL secobarbital. Bilirubin interference was less than 10.9 and less than 7.9%, respectively. The average recovery ranged from 85% to 94%. The mean difference in recovery in serum versus plasma was < or = 3%. Fifty-two clinical samples were analyzed for butalbital, pentobarbital, secobarbital, and phenobarbital by GC/MS, and the results were compared to the new Cassette Serum Barbiturates FPIA. The diagnostic sensitivity and specificity were 95% and 100%, respectively. Both FPIA and GC/MS assays are clinically efficacious for monitoring serum barbiturates.

Tricyclic Antidepressant Analysis by Reversed Phase Liquid Chromato-Graphy Using Phenyl Columns

Abstract Tricyclic antidepressant (TCA) analysis by reversed-phase liquid chromatography was achieved by a novel approach using two mini phenyl columns (4.5 × 50 mm). Analyses were organized into two drug groups: 1. n-desmethyl doxepin, doxepin, nortriptyline and amitriptyline, and 2. desipramine and imipramine. Sample preparation was modified from a published procedure (Wong and McCauley, J. Liq. Chrornatogr., 4, 849 (1981), using n-hexane/isoanyl alcohol (99:1) as the organic extractant, followed by back-extracting with dil. phosphoric acid. Both steps were carried out by using polypropylene tubes to minimize adsorptive

Challenges of toxicology for the millennium

In meeting the challenges of toxicology, clinical and forensic toxicologists should expand their services and engage in research and development to meet changing needs. Expanding roles could potentially derive from the threat of terrorism, genotyping for interpretation of potential toxic drug interactions, and criminalistic testings. At the threshold of the next millennium, terrorism via weapons of mass destruction (WMD) has migrated from the war zones to civilian settings. These WMD may be in the form of nuclear, biological, and chemical devices (NBC). Recently, the possible use of chemical/biological weapons in the Middle East conflicts, the use of sarin in a Tokyo subway station, and the unregulated availability of nuclear fuel in some countries all have heightened the potential for international and domestic NBC. In preparation for NBC, both government and civilians in major American cities have been trained for safe handling of patients and casualties. Forensic and clinical toxicologists should be knowledgeable about the clinical pharmacology, safe samples processing, and possible screening and/or analysis of samples exposed to or containing: vesicants; cyanide; and nerve, riot control, and pulmonary agents. These samples may be transported for further analysis and confirmed by designated central laboratories. In criminal/correctional settings, toxicologists should engage in quality assurance and consultation with attorneys, judges, and correctional professionals. With the emergence of pharmacogenetics, genotyping may enhance rational drug therapy for enhanced patient care, and may explain adverse or fatal drug reactions in postmortem analysis.