Marie Rosseel

Influence of hypovolemia on the pharmacokinetics and the electroencephalographic effect of propofol in the rat.

BackgroundHypovolemia decreases the dose requirement for anesthetics, but no data are available for propofol. As it is impossible to study this in patients, a rat model was used in which the influence of hypovolemia on the pharmacokinetics and pharmacodynamics of propofol was investigated. MethodsAnimals were randomly allocated to either a control (n = 9) or a hypovolemia (n = 9) group, and propofol was infused (150 mg · kg−1 · h−1) until isoelectric periods of 5 s or longer were observed in the electroencephalogram. The changes observed in the electroencephalogram were quantified using aperiodic analysis and used as a surrogate measure of hypnosis. The righting reflex served as a clinical measure of hypnosis. ResultsThe propofol dose needed to reach the electroencephalographic end point in the hypovolemic rats was reduced by 60% (P < 0.01). This could be attributed to a decrease in propofol clearance and in distribution volume. Protein binding was similar in both groups. To investigate changes in end organ sensitivity during hypovolemia, the electroencephalographic effect versus effect–site concentration relation was studied. The effect–blood concentration relation was biphasic, exhibiting profound hysteresis in both hypovolemic and control animals. Semiparametric minimization of this hysteresis revealed similar equilibration half-lives in both groups. The biphasic effect–concentration relation was characterized by descriptors showing an increased potency of propofol during hemorrhage. The effect–site concentration at the return of righting reflex was 23% (P < 0.01) lower in the hypovolemic animals, also suggesting an increased end organ sensitivity. ConclusionsAn increased hypnotic effect of propofol occurs during hypovolemia in the rat and can be attributed to changes in both pharmacokinetics and end organ sensitivity.

Determination of nifedipine in human plasma by capillary gas chromatography with nitrogen detection

A gas chromatographic method for the determination of nifedipine in human plasma is presented. Nifedipine was extracted from plasma at basic pH with toluene, and nitrendipine was used as the internal standard. Chromatography was performed on a cross-linked methylsilicone fused-silica column by on-column injection and with a nitrogen-phosphorus ionization detector. The minimal detectable concentration was approximately equal to 0.5 ng/ml of plasma. The standard curve was linear in the range evaluated, 2-300 ng/ml plasma. The within-analysis coefficient of variation was 3.9-10.4%, and the day-to-day coefficient of variation was 3.8%. A peak with the same retention time as the nitropyridine derivative of nifedipine was detected in the plasma of patients who had taken 10 mg nifedipine orally.

Determination of cetirizine in human urine by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of the histamine H1-receptor antagonist cetirizine in human urine was developed. Cetirizine and the internal standard are extracted from acidified (pH 5) urine (0.5 ml) into chloroform and the organic layer is evaporated to dryness. The residue is chromatographed on a Spherisorb 5ODS-2 column using Pic A (5 mM aqueous tetrabutylammonium phosphate)-methanol-tetrahydrofuran (33:65:2, v/v) as the mobile phase with ultraviolet detection (230 nm). The calibration graph is linear from 0.1 to 10 micrograms/ml and using 0.5 ml of urine the detection limit is 20 ng/ml. The within-run relative standard deviation is less than 6% and the accuracy is within 10% of the theoretical value at concentrations between 0.1 and 10 micrograms/ml in urine. There is a good correlation (r = 0.99606) with a previously described capillary gas chromatographic assay.

Reversed-phase high-performance liquid chromatographic analysis of atenolol enantiomers in plasma after chiral derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A sensitive high-performance liquid chromatographic method for the determination of the enantiomers of atenolol in rat plasma has been developed. Racemic atenolol and practolol (internal standard) were extracted from alkalinized plasma (pH 12) into dichloromethane containing 3% (v/v) heptafluoro-1-butanol, and the organic layer was evaporated. The samples were derivatized with (+)-1-(9-fluorenyl)ethyl chloroformate at pH 8.5 for 30 min. After removal of excess reagent, the diastereomers were extracted into dichloromethane. The diastereomers were separated on a Microspher C18 column (3 microns) with a mobile phase of acetonitrile-sodium acetate buffer (0.01 M, pH 7) (50:50, v/v) at a flow-rate of 0.8 ml/min. Fluorescence detection (lambda ex = 227 nm, lambda em = 310 nm) was used. When 100 microliters of plasma were used, the quantitation limit was 10 ng/ml for the atenolol enantiomers. The assay was applied to measure concentrations of atenolol enantiomers in plasma after intravenous administration of racemic atenolol to rats.

The influence of hemorrhagic shock on the pharmacokinetics and the analgesic effect of morphine in the rat

Summary— The influence of hemorrhagic shock (removal of 30% of the blood volume) on the pharmacokinetics and the analgesic effect of morphine was investigated in conscious rats. Plasma concentrations of morphine after a bolus injection (5 mg/kg) are higher in the shock animals, which is attributed to a small decrease in clearance (‐22%; P > 0.05) and a significant decrease in distribution volume (‐33%; P < 0.05) of the drug. The areas under the plasma concentration‐time curve of the metabolite morphine‐3‐glucuronide (M3G) are significantly higher (+237%; P < 0.01) in the shock rats, which is probably explained by a decreased distribution and renal excretion. The analgesic effect of morphine was evaluated using the tail‐flick test during a continuous infusion (10 mg/kg/h) with measurement of the plasma concentrations of morphine and M3G. Data from these experiments show higher plasma concentrations of morphine (+33%; P < 0.05) and M3G (+66%; P > 0.05) during shock, and a significantly increased analgesic effect (+43%; P < 0.05). Our data suggest that the increased analgesic effect of morphine during hemorrhagic shock can most likely be explained by pharmacokinetic changes resulting in higher morphine concentrations.

Effects of smoking, CYP2D6 genotype, and concomitant drug intake on the steady state plasma concentrations of haloperidol and reduced haloperidol in schizophrenic inpatients.

The effects of smoking, CYP2D6 genotype, and concomitant use of enzyme inducers or inhibitors on the steady state plasma concentrations of haloperidol (HAL) and reduced haloperidol (RHAL) were evaluated in 92 schizophrenic inpatients. All but three of these patients received concomitant medication, in many cases with drugs potentially interacting with HAL. Of the 92 patients, 63 were treated orally with HAL in a daily dose of 0.4 to 50 mg; 29 patients were treated intramuscularly with a daily equivalent dose of HAL decanoate (expressed as HAL) of 1.8 to 17.9 mg. A wide interindividual variation in HAL dose and in steady state plasma concentrations of HAL and RHAL was observed. In the patients treated orally, the daily oral dose was about 4 times higher and the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers (n = 40) than in nonsmokers (n = 23) (p < 0.01). The dose-normalized RHAL (but not HAL) plasma concentrations and the RHAL/HAL ratio were significantly higher in poor metabolizers (PMs) than in extensive metabolizers (EMs). There was a trend toward an effect of potentially interacting drugs (inducers or inhibitors) on dose, dose-normalized HAL and RHAL plasma concentrations, and the RHAL/HAL ratio. In the patients treated intramuscularly, the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers than in nonsmokers, but no differences in doses were observed. This naturalistic study of modest sample size in a polymedicated population shows an effect of smoking and CYP2D6 genotype (and to a lesser extent, of interacting drugs) on the kinetics of HAL.

High performance liquid chromatography determination of dextromethorphan and its metabolites in urine using solid-phase extraction.

A high performance liquid chromatography assay coupled with fluorescence detection was developed for the determination of dextromethorphan and its metabolites in urine. The products and the internal standard, pholcodine, were separated on an Alltima C18, 5 microns column (250 x 4.6 mm), using a mobile phase containing sodium dodecyl sulphate (1 mM) in a mixture of acetonitrile-sodium dihydrogen phosphate (0.01 M) 40.5:59.5, v/v) (pH* = 2.5). A novel solid-phase extraction procedure with strong cation exchange, non end-capped, Isolute SCX cartridges allows good recovery of the products (mean 85% or more). For all analytes, the assay is sensitive (LOQ 25 ng ml-1, using 200 microliters urine), reproducible (RSD < 15%) and accurate (< 15% deviation of the nominal value) over the range evaluated. This method can be used to measure dextromethorphan and its metabolites to phenotype individuals as poor or extensive metabolizers of drugs metabolized by CYP2D6.

Relationship Between Etomidate Plasma Concentration and EEG Effect in the Rat

AbstractPurpose. The effect-plasma concentration relationship of etomidate was studied in the rat using electroencephalographic changes as a pharmacodynamic parameter. Methods. Etomidate was infused (50 mg/kg/h) in chronically instrumented rats (n = 6) until isoelectric periods of 5 s or longer were observed in the electroencephalogram (EEG). The EEG was continuously recorded during the experiment and frequent arterial blood samples were taken for determination of etomidate plasma concentrations. The changes observed in the raw EEG signal were quantified using aperiodic analysis in the 2.5−7.5 Hz frequency band. The return of the righting reflex was used as another parameter of anesthesia. Results. A mean dose of 8.58 ± 0.41 mg/kg needed to be infused to reach the end point of 5 s isoelectric EEG. The plasma concentration time profiles were most adequately fitted using a three-exponential model. Systemic clearance, volume of distribution at steady-state and elimination half-life averaged 93 ± 6 ml/min/kg, 4.03 ± 0.24 l/kg and 59.4 ± 10.7 min respectively. The EEG effect-plasma concentration relationship was biphasic exhibiting profound hysteresis. Semi-parametric minimization of this hysteresis revealed an equilibration half-life of 2.65 ± 0.15 min, and the biphasic effect-concentration relationship was characterized nonparametrically by descriptors. The effect-site concentration at the return of the righting reflex was 0.44 ± 0.03 μg/ml. Conclusions. The results of the present study show that the concentration-effect relationship of etomidate can be characterized in individual rats using aperiodic analysis in the 2.5−7.5 Hz frequency band of the EEG. This characterization can be very useful for studying the influence of diseases on the pharmacodynamics of etomidate in vivo.

Measurement of cefuroxime in human bronchoalveolar lavage fluid by high-performance liquid chromatography after solid-phase extraction

A sensitive and selective method for the determination of cefuroxime in bronchoalveolar lavage (BAL) fluid using high-performance liquid chromatography (HPLC) with UV detection at 280 nm after solid-phase extraction with C18 cartridges was developed. A Waters symmetry C18 column was used and the mobile phase was acetonitrile-0.05 M ammonium phosphate buffer (pH 3.2) (15:85, v/v). The method enabled the determination of cefuroxime at concentrations below 100 ng/ml, with a linear calibration curve at concentrations of 5-100 ng/ml for 400 microliters of BAL. The intra- and inter-assay coefficient of variations for 10, 40 and 80 ng/ml were between 5.3 and 8.9%. Analytical recoveries were between 92.7 and 106.2%. The detection limit was 1 ng/ml at a signal-to-noise ratio of 3:1 using 400 microliters of BAL. The method was successfully used for the analysis of BAL fluid from patients after oral administration of 500 mg cefuroxime axetil twice daily.

Comparison of Two high-performance liquid chromatographic methods for monitoring plasma concentrations of haloperidol and reduced haloperidol

Two high-performance liquid chromatographic methods for monitoring haloperidol (HAL) and reduced haloperidol (RHAL) plasma concentrations were compared. In one method ultraviolet detection and a C18 column were used (UV method); in the other method electrochemical detection and a CN-column were used (EC method). Both methods are accurate and precise. For plasma samples spiked with HAL or RHAL, an excellent correlation was observed between the concentrations of HAL and RHAL found with both methods (r < or = 0.99, p < 0.01). However, for plasma obtained from patients treated with HAL the correlation between the two methods was poor (r > or = 0.71, p < 0.01). The main reason for the discrepancy between the two methods is probably interference of comedications or their metabolites, mostly in the EC method. Although the quantitation limit of the UV method (2 ng/ml for HAL and RHAL) is higher than that of the EC method (0.5 ng/ml for HAL and RHAL), the UV method is to be preferred for monitoring plasma levels in psychiatric patients because there is less interference from comedication.