PubMed Health⌕ Search

Biomedical subjects

B Lacarelle

Publications and source records attributed to B Lacarelle.

At least 55 records · Page 3Linked to original sources
PubMed1994

Monitoring of pefloxacin serum concentrations in intensive care unit patients: comparison of a new immunoassay with high-performance liquid chromatography.

Serum quinolone concentrations are not routinely measured in clinical practice. However, in order to optimize quinolone treatment, monitoring of serum concentrations could sometimes be useful particularly in critically ill patients. A new enzyme-linked immunosorbent assay (ELISA) that permits direct determination of pefloxacin in serum is described. To validate this new assay, pefloxacin concentrations were measured in 314 serum samples from 74 intensive care unit patients treated with pefloxacin (400 mg i.v. twice daily). Reference concentrations were obtained by reverse phase high-performance liquid chromatography (HPLC) with spectrofluorometric detection. Results showed that concentrations measured by ELISA correlated very well with those by HPLC (r = 0.957; y = 1.03 and x -0.15). In this population, the concentrations found by ELISA varied between individuals (Cmin = 0.70-39 micrograms/ml; Cmax = 5.2-40 micrograms/ml). However, 86% of the measured Cmax and Cmin levels were adequate for optimal pefloxacin therapy. Only 11% of Cmin and 14% of Cmax were below the optimal values (i.e., 2 and 8 micrograms/ml, respectively). These results suggest that despite the large therapeutic index of pefloxacin, monitoring of its serum concentrations using a rapid ELISA technique may be useful for optimal antimicrobial treatment of certain intensive care unit patients.

Adolescent↗
PubMed1994

[Hepatic transport of mitoxantrone in relation to multiple resistance].

We have examined the effect of cyclosporin A on transport processes (uptake, efflux, binding) of mitoxantrone in isolated rat liver cells. Accumulation and binding of mitoxantrone was rapid with or without cyclosporin A. The initial uptake was linear over a wide concentration range (1 to 1000 microM). For the first 100 s, the rate of uptake is constant. The uptake clearance ranged from 12.53 +/- 3.9 to 33.77 +/- 15.1 nl.min-cell-1 for different extracellular concentrations of mitoxantrone. Also cyclosporin A did not modified this coefficient. Initial binding of mitoxantrone to cell plasma membrane was estimated and it was modified by different extracellular concentrations of mitoxantrone but not by cyclosporin A. Respectively at 60 seconds it accounted to 79.6% and 81.6% of the total transport. Influx of mitoxantrone was not temperature sensitive. We next examined the efflux of mitoxantrone from cells that were preloaded with drug. Initial efflux was rapid for the first 5 minutes. Cyclosporin A slightly decrease this efflux (7%). The data suggest that the mechanism of uptake of mitoxantrone is passive diffusion and that cyclosporin A a p-glycoprotein 170 inhibitor agent has only a weak effect on efflux.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Inhibitory effects of anticancer drugs on dextromethorphan-O-demethylase activity in human liver microsomes.

The dextromethorphan-O-demethylase activity determined in human liver microsomes was used to screen various anticancer drugs for their ability to inhibit this cytochrome CYP2D6-dependent activity. Competitive inhibition indicates that the drug binds the enzyme and is potentially subjected to a polymorphic metabolism. Among the 13 anticancer drugs tested, 4 compounds caused competitive inhibition of dextromethorphan-O-demethylation: lomustine (Ki = 7.7 microM), doxorubicin (Ki = 75 microM), vinorelbine (Ki = 22 microM), and vinblastine (Ki = 42 microM). The results of these studies indicate that the metabolism of the drugs concerned is possibly altered in poor metabolizers of debrisoquine and requires further investigation to study their specific routes of biotransformation. The metabolism of these drugs probably involves various biotransformation pathways, among which the CYP2D6-dependent route would be of minor importance. A second hypothesis is that these drugs could be inhibitors of the isozyme without being a substrate.

Antineoplastic Agents↗
PubMed1992

Evaluation of Bayesian estimation in comparison to NONMEM for population pharmacokinetic data analysis: application to pefloxacin in intensive care unit patients.

The pharmacokinetics of pefloxacin (PF) were investigated in a population of 74 intensive care unit patients receiving 400 mg bid as 1-hr infusion using (i) Bayesian estimation (BE) of individual patient parameters followed by multiple linear regression (MLR) analysis and (ii) NONMEM analysis. The data consisted of 3 to 9 PF plasma levels per patient measured over 1 to 3 dosage intervals (total 113) according to four different limited (suboptimal) sampling 3-point protocols. Twenty-nine covariates (including 15 comedications) were considered to explain the interpatient variability. Predicted PF CL for a patient with median covariates values was similar in both BE/MLR and NONMEM analysis (4.02 and 3.92 L/hr, respectively). Bilirubin level and age were identified as the major determinants of PF CL by both approaches with similar predicted magnitude of effects (about 40 and 30% decrease of median CL, respectively). Confounding effects were observed between creatinine clearance (26% decrease of PF CL in the BE/MLR model), simplified acute physiology score (a global score based on 14 biological and clinical variables) (18% decrease of median CL in the NONMEM model) and age (entered in both models) which were highly correlated in our data base. However, both models predicted similar PF CL for actual subpopulations by using actual covariate values. Finally, the NONMEM analysis allowed identification of an effect of weight on CL (decrease of CL for weight < 65 kg) whereas the BE/MLR analysis predicted an increase of CL in patients treated with phenobarbital. In conclusion, both approaches allowed identification of the major risk factors of PF pharmacokinetics in ICU patients. Their potential use at different stages of drug development is discussed.

Adolescent↗
PubMed1992

Thawed human hepatocytes in primary culture.

In drug metabolism studies, isolated and cultured human hepatocytes provide a useful model for overcoming the difficulty of extrapolating from animal data. In vitro studies with human hepatocytes are scarce because of the lack of livers and suitable methods of storage. After developing a new method for cryopreservation of human hepatocytes, we evaluated the effects of deep freezing storage on their viability, morphology, and functional and toxicological capabilities in classical culture conditions. Freshly isolated human hepatocytes were cryopreserved in medium containing 10% Me2SO and 20% fetal calf serum, using a Nicool ST20 programmable freezer (-1.9 degrees C/min for 18 min and -30 degrees C/min for 4 min). Cells were stored in liquid nitrogen. Viability of thawed human hepatocytes was 50-65% as assessed by erythrosin exclusion test prior to purification on a Percoll density gradient. Morphological criteria showed that thawed human hepatocytes require an adaptation period to the medium after seeding. Functional assessments showed that human hepatocytes which survive freezing and thawing preserve their protein synthesis capabilities and are able to secrete a specific protein, anionic peptidic fraction, which is involved in the hepatic uptake of bile-destined cholesterol. We then studied Midazolam biotransformation to test metabolic functions, and erythromycin toxicity by Neutral Red test (cell viability) and 3-(4,5-dimethylthiazol-2-yl)-diphenyl tetrazolium bromide test (cell metabolism). All of these experiments indicated that thawed human hepatocytes should be used 38 h after seeding for optimum recovery of their functions: membrane integrity, protein synthesis, and stabilization of drug metabolism enzymes.

Biotransformation↗
PubMed1992

Pharmacodynamic properties of propofol during recovery from anaesthesia.

Propofol was used to induce and maintain anaesthesia in 20 healthy adult ASA physical status 1 patients undergoing dental surgery. Recovery was studied using psychometric tests and clinical assessment while propofol blood levels were obtained at the same study times. Recovery was rapid and there were no significant differences 60 min after anaesthesia (t60) for the tracing test and 90 min for the choice reaction time. All patients were orientated in time at t30 and in space at t45; Stewart's score was maximal in all patients at t60; recovery of normal walking was slower, i.e. t120. Return to baseline for psychometric function was linked to a decrease in propofol blood level, for both the tracing test (P less than 10(-6)) and the choice reaction time (P less than 10(-3)). We conclude that propofol is a suitable anaesthetic agent for induction and maintenance of short duration dental anaesthesia.

Adult↗
PubMed1991

Metabolism of digoxin, digoxigenin digitoxosides and digoxigenin in human hepatocytes and liver microsomes.

In vitro metabolism of digoxin and its cleavage-related compounds was investigated using hepatocytes in primary culture and microsomal fractions both isolated from human livers. On these models, digoxin (DG3) and digoxigenin bisdigitoxoside (DG2) were not shown to be significantly metabolized in vitro in man. Therefore, it appeared that the stepwise cleavage of DG3 and DG2 sugars was not cytochrome P450 dependent. This enzymatic system probably plays a minor role in humans for this particular reaction. However, digoxigenin monodigitoxoside (DG1) and digoxigenin (DG0) which are known to be formed after intra-gastric hydrolysis of DG3, were extensively converted to polar compounds (mainly glucuronides). In addition, using human liver microsomes, a wide variability in UDP-glucuronyl transferase (UDPGT) activities responsible for DG1 glucuronidation was demonstrated. These results suggest that two main factors may contribute to the overall interindividual variability of digoxin biotransformation: 1), the individual intra-gastric pH which influences the sugar cleavage leading to DG1 and DG0; ii), a variability in the level of the hepatic UDPGT specific for digitalis compounds conjugation.

Biotransformation↗
PubMed1991

Metabolism of minaprine in human and animal hepatocytes and liver microsomes--prediction of metabolism in vivo.

1. The metabolism of minaprine and its major metabolite p-hydroxyminaprine were studied using hepatocytes and liver microsomes from different species. Metabolism of this drug in vitro was then compared with in vivo data already published. 2. Our results showed that the major metabolic route (4-hydroxylation of the aromatic ring) is the same in the two experimental systems. Other in vivo biotransformation pathways (i.e. N-oxidation, reductive ring cleavage, N-dealkylation, oxidation) were also confirmed in hepatocytes. 3. Similar inter-species variability was observed both in vitro and in vivo. The present study has led to the same conclusion as previous in vivo metabolic investigations, namely, that metabolism in the dog quantitatively differs from that observed in other animal species. 4. These results clearly demonstrate that in vitro models (i.e. isolated hepatocytes and liver microsomes) are powerful tools in predicting the metabolic pathways of a drug in man and animal species.

Adsorption↗
PubMed1991

Use of human and animal liver microsomes in drug metabolic studies.

A bank of readily available well-characterized human and animal hepatic microsomal fractions has been established. By using these "in vitro" models, we evidenced large interspecies variabilities for various compounds including digoxin, minaprine and two vincaalkaloïds (navelbine, vinblastine). Therefore, extrapolation from animal to human appeared limited and we focused our interest on human liver microsomes. Enzymatic characteristics of human microsomes from 35 different livers were determined using specific monooxygenase (i.e. erythromycin, aniline, aminopyrin...) and UDP-glucuronosyltransferase substrates (i.e. p-nitrophenol, monodigitoxoside digitoxigenin...). A wide variability was thus ascertained between individual for both phase I and phase II metabolic processes. Microsomal fractions were also shown to be of great interest for assessing the P450 cytochrome isoform(s) involved in the biotransformation of a given drug. For instance, using inhibitory experiments, we showed the implication of P450IID in minaprine metabolism. We also demonstrated that P450IIIA is probably involved in vindesine biotransformation. Drug metabolic interactions between cyclosporin A and macrolides were studied using the same model. These results demonstrating that erythromycin is a much more potent inhibitor of cyclosporin A biotransformation than spiramycin, agree closely with "in vivo" data. In conclusion, liver microsomes are powerful tools in studying: i) interspecies and interindividual variabilities, ii) metabolic drug interactions.

Animals↗
PubMed1990

Pharmacokinetics of long-term propofol infusion used for sedation in ICU patients.

The pharmacokinetics of propofol were determined in nine patients (seven men, two women, (mean +/- SD) 55.8 +/- 21.2 yr, 65.2 +/- 8 kg) requiring prolonged mechanical ventilation of their lungs. After an initial dose of 1-3 mg/kg, propofol was administered iv at 3 mg/kg/h for 72 h. Arterial blood samples were collected at selected times during and up to 72 h after infusion. Propofol whole blood concentrations were determined by high-performance liquid chromatography with fluorescence detection. Individual pharmacokinetic parameters were estimated by noncompartmental analysis. Derived pharmacokinetic parameters showed a long terminal phase (T1/2 = 1878 +/- 672 min), a large volume of distribution at steady state (Vdss = 1666 +/- 756 l), and a high total body clearance (Cl = 1.57 +/- 0.56 l/min). While the propofol terminal elimination half-life is longer than that previously reported, emergence from sedation after prolonged administration will be governed by both redistribution mechanisms arising from the large distribution volumes and elimination from the body.

Adult↗
PubMed1987

[Recovery after anesthesia with propofol in otorhinolaryngologic surgery of brief duration].

This study was designed to assess recovery from total intravenous anaesthesia with propofol for short ENT procedures. Twenty-six patients (ASA I and II) were assigned to two groups of thirteen: one breathed air (Laser laryngeal microsurgery), the second N2O-O2 (FIO2 : 0.5) (various ENT procedures). The induction sequence was exactly the same for both groups: oral premedication with 10 mg diazepam one hour before surgery, I mg pancuronium bromide, 2 micrograms X kg-1 fentanyl, denitrogenation within 3 min, after which propofol was delivered (2.5 mg X kg-1). When the eye-lash reflex had disappeared (time recorded), 1.5 mg X kg-1 suxamethonium was given and laryngotracheal intubation carried out. A continuous infusion of propofol (9 mg X kg-1 X h-1) was started. Surgery began 5 +/- 2 min after the start of propofol infusion. The durations of anaesthesia, surgery and propofol infusion were similar in both groups. To have good surgical conditions, it was necessary to give repeated doses of propofol for 15 patients. Thus, the total dose of propofol was significatively different between the two groups: 24.5 +/- 6.7 mg X kg-1 X h-1 in group "air" versus 16 +/- 3.6 mg X kg-1 X h-1 in group "N2O-O2" (p less than 0.001). Extubation occurred within 16 +/- 8 min in group "air", being more rapid in group "N2O-O2" (11 +/- 9 min; no significant difference). Recovery was assessed with two psychomotor tests: choice reaction time (CRT) and tracing test (TT).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Evaluation of a Bayesian method of amikacin dosing in intensive care unit patients with normal or impaired renal function.

Our study was designed to determine the population pharmacokinetic parameters of amikacin in intensive care unit patients and to develop a Bayesian method allowing individual estimation of pharmacokinetic parameters. A two-stage method was used for estimating the population characteristics of the pharmacokinetic parameters. Calculations of optimum doses and dosing intervals were based on individual parameters. Our results indicate that the Bayesian method is capable of estimating the individual pharmacokinetic parameters with no significant bias and good precision. Individualization of amikacin dosage was assessed 70 times in 52 patients. To determine the predictive performance of the method, observed peak and trough levels were compared with predicted values by computing precision, bias, and correlation. The amikacin dosing method was unbiased and showed a high correlation coefficient (r = 0.962) between measured and predicted drug serum concentrations. No significant differences were found between the predicted and observed peak (17.3 +/- 3.5 and 17.3 +/- 3.8 micrograms/ml, respectively) and trough (2.86 +/- 0.93 and 3.08 +/- 1.41 micrograms/ml, respectively) amikacin serum concentrations. Among the 52 patients, wide variations were observed in the pharmacokinetic parameters (Vd = 0.21-0.50 L/kg; t 1/2 = 1.1-22 h) and the daily doses (2.8-42 mg/kg/day).

Adolescent↗
PubMed1987

Validation of a radioreceptor assay technique for monitoring pharmacological active material during intensive diazepam tetanus therapy.

The present study's aim was to monitor the daily plasma levels of diazepam and its metabolites in two tetanic patients who were receiving very strong doses of diazepam in continuous infusion. The kinetics of high doses of diazepam were estimated. These plasma levels were determined selectively using gas-liquid chromatography (GLC), then correlated with a global estimation by radioreceptor-assay (RRA). At the end of the infusion, the kinetics of diazepam and of RRA active material were calculated using a linear, open, two compartment model. Muscle-relaxant and residual sedative effects were clinically monitored. The mean concentrations of diazepam (2.33, 0.60 micrograms/ml), desmethyldiazepam (3.27, 1.00 micrograms/ml) and oxazepam (0.73, 0.47 micrograms/ml) estimated by GLC and of RRA active material (5.62, 1.08 micrograms/ml) correlated better when active metabolites were considered (r = 0.898) than when diazepam alone was taken into account (r = 0.730), indicating that these metabolites influence the overall activity of the parent compound. Half-lives of RRA results (52.6 h for patient 1 and 82.5 h for patient 2) were higher than those of diazepam estimated using GLC results (21.2 h for patient 1 and 42.3 h for patient 2). This could be related to the contribution of the active metabolites and might explain the residual sedative effect observed for at least seven days following cessation of the diazepam (DZP) infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Biotransformation↗
PubMedDate not supplied

Direct determination of mitoxantrone in plasma by high performance liquid chromatography using an automatic precolumn-switching system as sample clean-up procedure.

A high-performance liquid chromatography method which uses direct injection and a column-switching valve for determination of mitoxantrone in plasma is described. After addition of internal standard, plasma was deproteinized by adding 5-sulphosalicylic acid reagent. The supernatant was injected onto an enrichment precolumn flushed with washing solvent (methanol and water 5:95). Absorbed mitoxantrone was backflushed from the precolumn into an analytical column C18 Nucleosil 250 x 4 mm with a gradient elution (solvent A, ammonium formate buffer 1.6 M, pH 4.3; solvent B, acetonitrile and water 40:60; linear gradient from 45 to 55% of B for 30 min was programmed) at a flow rate of 1.3 mL/min. Detection was carried out at 665 nm. This method showed obvious advantages over conventional extraction procedures in terms of speed and facility of sample handling.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Involvement of the cytochrome P-450IID subfamily in minaprine 4-hydroxylation by human hepatic microsomes.

4-Hydroxylation of minaprine was measured on microsomal fractions prepared from 25 different human liver samples. In vitro formation of 4-hydroxyminaprine exhibited a large interindividual variability. Indeed, minaprine 4-hydroxylase activity ranged between 0.033 and 0.421 nmol/min/mg microsomal protein. Two samples presented a particularly low enzyme activity. Minaprine 4-hydroxylation followed Michaelis-Menten kinetics with KM and Vmax values of 5.26 microM and 0.478 nmol/min/mg microsomal protein, respectively, for one particular representative sample. The effects of various compounds (substrates or inhibitors of cytochrome P-450 isoforms) on 4-hydroxyminaprine formation were investigated. Selective substrates for P-450IA [benzo(a)pyrene, theophylline, and phenacetin], IIC (hexobarbital), IIE (aniline), and IIIA (erythromycin, nifedipine, and troleandomycin) cytochrome subfamilies did not inhibit 4-hydroxyminaprine formation. The nonspecific cytochrome P-450 inhibitor, cimetidine, slightly inhibited minaprine 4-hydroxylation. The classical substrates of the P-450IID cytochrome subfamily (debrisoquine, propranolol, and sparteine) inhibited minaprine 4-hydroxylation, as did the known P-450IID specific inhibitor, quinidine. These compounds inhibited minaprine 4-hydroxylase with Ki values of 16.5 (debrisoquine), 14.4 (propranolol), 61.9 (sparteine), and 0.146 microM (quinidine). 4-Hydroxyminaprine formation rate was shown not to be correlated with the activity of both erythromycin N-demethylase (r = 0.29, non-significant) and aniline hydroxylase (r = -0.15, NS). In contrast, minaprine 4-hydroxylase was well correlated with both debrisoquine 4-hydroxylase activity (r = 0.501, p less than 0.05) and immunoquantified cytochrome P-450IID6 (r = 0.579, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome P-450 Enzyme Inhibitors↗