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Biomedical subjects

Nicolas Simon

Publications and source records attributed to Nicolas Simon.

17 recordsLinked to original sources

Effects of ursodeoxycholic acid on P-glycoprotein and cytochrome P450 3A4-dependent pharmacokinetics in humans.

BACKGROUND AND OBJECTIVE: On the basis of in vitro studies indicating that ursodeoxycholic acid (UDCA) is a cytochrome P450 (CYP) 3A4 inducer and a pregnane X receptor activator and because the pregnane X receptor is a transcriptional regulator of multidrug resistance 1 (MDR1)/P-glycoprotein (P-gp), we postulated that UDCA might decrease the bioavailability of CYP3A4 and P-gp probe drugs in humans. The main objective of this study was to determine whether UDCA alters the pharmacokinetics of digoxin and midazolam. The secondary objective was to determine whether the intestinal expression of P-gp and CYP3A4 is increased by UDCA. METHODS: The effect of UDCA on MDR1 and CYP3A4 messenger ribonucleic acid (mRNA) expression was investigated in human colon carcinoma cell lines LS174T and Caco-2. Eight healthy volunteers participated in this open, nonrandomized 2-period study, in which the effects of UDCA (13 mg.kg(-1).d(-1) during 2 weeks) versus control on the pharmacokinetics of digoxin (0.5-mg single intravenous infusion), d3-digoxin (3-fold deuterated digoxin, 0.5-mg single oral dose), and midazolam (7.5-mg single oral dose) were compared. Duodenal biopsy specimens were obtained during both periods to quantify MDR1/P-gp and CYP3A4 expression. RESULTS: In vitro UDCA induced MDR1 and CYP3A4 mRNA in Caco-2 cells but not in LS174T cells. In humans UDCA significantly decreased the extent of digoxin absorption from 0.77 to 0.70 and the oral d3-digoxin area under the plasma concentration-time curve from 0 to 4 hours from 6.4 +/- 1.7 ng.h.mL(-1) to 5.3 +/- 1.5 ng.h.mL(-1) (P = .01 and P = .05, respectively). UDCA had no detectable effects on the pharmacokinetics of midazolam or the intestinal mRNA and protein expression levels of MDR1/P-gp and CYP3A4. CONCLUSION: Under the conditions in our study, UDCA only modestly decreased digoxin disposition without detectable changes in midazolam pharmacokinetics. The clinical relevance of these findings remains to be determined.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Effects of a seven-day continuous infusion of ropivacaine on circadian rhythms in the rat.

The present study was conducted to evaluate the effect of a 7 d continuous infusion of ropivacaine on the 24 h rhythms of body temperature, heart rate, and locomotor activity. After an initial 7 d baseline, rats were randomly divided into two groups of 4 rats each to receive ropivacaine or saline via an osmotic pump for 7 consecutive days. The pumps were removed thereafter and observed during a 7 d recovery span. The studied circadian rhythms were measured by radiotelemetry throughout each of the 7 d periods. An additional group of 4 rats was studied under the same experimental conditions to assess the plasma levels of ropivacaine on days 3 and 8 following pump implantation. Our results indicate that ropivacaine does not induce loss of the circadian rhythms of body temperature, heart rate, or locomotor activity; a prominent period of 24 h was found for all variables in all animals, before, during, and after ropivacaine treatment. However, ropivacaine treatment did modify some characteristics of the rhythms; it increased the MESOR (24 h mean) of the heart rate and locomotor activity rhythms and advanced the acrophase (peak time) of the locomotor activity circadian rhythm. The present study indicates that the circadian rhythms of heart rate and locomotor activity are modified after continuous infusion of ropivacaine, which is of particular interest, given the potential cardiotoxicity of this local anesthetic agent.

Amides↗

Cyclosporine monitoring in renal transplant recipients with induction therapy: C2 levels in patients monitored on C0.

The aim of this retrospective study was to compare the cyclosporine C(2) blood levels in renal transplant recipients with induction therapy, monitored on C(0) levels during the early and long-term post-transplantation periods in different French transplantation centres, to the target values recommended by the International Consensus on Neoral and used in the Mo2art study. A retrospective study was conducted by the therapeutic drug monitoring (TDM) committee of the French Pharmacological Society. Cyclosporine C(0) and C(2) concentrations from 168 renal transplant recipients were collected at different post-transplantation periods by six TDM laboratories of transplantation centres from April 2001 to April 2002. Cyclosporine blood levels were determined by fluorescence polarization immunoassay (mFPIA, AxSYM, Abbott) or enzyme immunoassay (EMIT, Dade Behring). Most patients had C(0) values in the recommended target ranges, with C(2) levels below the targets used in the Mo2art study or proposed by the International Consensus Conference, both during the early and long-term post-transplantation periods. Sixty-eight per cent of patients had C(2) below 1,500 microg/L +/- 20% in the first 2 months post-transplantation and 55% had C(2) below 800 microg/L +/- 20% in the late post-transplantation period (>1 year). Cyclosporine dose should be increased by 40% on average during the first week post-transplantation period and by 50% during the maintenance period to achieve the C(2) targets. In France, most renal transplant recipients receiving induction agents monitored on C(0) had C(2) levels below the targets recommended by the International Consensus Conference. In clinical practice, the optimal therapeutic windows for CsA monitoring based on C(2) needs to be more precisely defined, both during the early and long-term post-transplantation periods in renal transplant recipients receiving induction agents.

Antibodies, Monoclonal↗

Population pharmacokinetics of ceftriaxone and pharmacodynamic considerations in haemodialysed patients.

OBJECTIVES: To determine the pharmacokinetic parameters of ceftriaxone following an infusion in haemodialysed outpatients and to use these parameters for an optimisation of dosing based on pharmacodynamic indices. METHODS: Fifty haemodialysed patients were enrolled in a single-centre, prospective, open-label study. They received short intravenous infusions of ceftriaxone 1 or 2 g every 48 hours for bronchopneumonia immediately after the dialysis session. Total plasma concentrations of ceftriaxone were analysed with a population pharmacokinetic approach using nonlinear mixed-effects modelling. Free drug concentrations were derived from published binding parameters in order to estimate the time when they exceed the minimum inhibitory concentration (MIC). RESULTS: The pharmacokinetics were best described by a two-compartment model. None of the covariates tested (age, bodyweight, height, sex, body mass index, albumin) influenced the pharmacokinetic parameters. The estimated population pharmacokinetic parameters (interindividual variability [percentage of coefficient of variation]) were clearance 0.36 L/h (48%), volume of distribution of the central compartment 4.53 L (47%), intercompartmental clearance 10.8 L/h and volume of distribution of the peripheral compartment 9.54 L (63%). The terminal elimination half-life (t(1/2)beta) from plasma was 27.5 hours. The mean (range) times when the free drug concentration exceeded the MIC (T>MIC) following ceftriaxone 1 g infusion were 60.3 (53.0-67.7) hours and 2.5 (1.0-3.9) hours for the breakpoints 1 and 8 mg/L (based on free drug concentration), respectively. After administration of ceftriaxone 2 g, the T>MIC was 88.5 (78.8-98.3) hours and 17.7 (13.3-22.0) hours for the breakpoints 1 and 8 mg/L, respectively. The simulated free drug concentrations (median, first and third quartile) for 48 and 72 hours following the first dose of ceftriaxone 1g were 1.11, 0.63 and 1.89 mg/L, and 0.63, 0.28 and 1.18 mg/L, respectively. For ceftriaxone 2g infusion, the simulated free concentrations (median, first and third quartile) at 48 and 72 hours were 2.50, 1.40 and 4.52 mg/L, and 1.37, 0.60 and 2.70 mg/L, respectively. CONCLUSIONS: On the basis of decreased clearance in haemodialysed patients, it can be argued that the dose of ceftriaxone should be decreased or the delay between doses should be increased. However, taking into account pharmacodynamic considerations, this study showed that following intravenous administration of ceftriaxone 1 g after each dialysis session, some patients were at risk of achieving a concentration below the MIC (1 mg/L), particularly if the second administration occurred 72 hours after the first dosing. Thus, a dose of ceftriaxone 2 g intravenously is recommended immediately following dialysis, particularly in patients with severe infections or when the dosing interval will be higher than 48 hours.

Adult↗

Review in pharmacokinetic models on corticosteroids.

The pharmacokinetics of corticosteroids provides a large set of mathematical models which led to analyse many kinetic profiles corresponding to many clinical and/or physiological situations. In this paper, we present a review on the usefulness, advantages and limits of such models which could find a large application in medicinal chemistry.

Adrenal Cortex Hormones↗

End-of-dose akinesia after a single intravenous infusion of the dopaminergic agonist piribedil in Parkinson's disease patients: a pharmacokinetic/pharmacodynamic, randomized, double-blind study.

This randomized, double-blind trial was designed to define the possible relationship between piribedil plasma concentrations and the decrease of the Unified Parkinson's Disease Rating Scale (UPDRS) motor score or the switch from off to on state after single intravenous infusion. Ten fluctuating patients with idiopathic Parkinson's disease (PD) received escalating doses of piribedil (2-16 mg) and placebo. Starting from 2 mg, piribedil was effective in reducing the motor deficit (UPDRS, motor score) including akinesia at the first evaluation time point of 15 minutes, and in reversing off state of 7 of 10 patients. The doses were equally effective, although the effect was more sustained with the highest dose of 16 mg. Piribedil was well tolerated up to a 16-mg dose and pharmacokinetics were linear up to the 16-mg dose. Plasma levels of piribedil were not correlated to the motor score improvement or switch from off-->on. In conclusion, a short single infusion of piribedil at 2 to 16 mg was safe and effective in improving motor symptoms, including akinesia, of fluctuating PD patients.

Aged↗

Cluster analysis: an alternative method for covariate selection in population pharmacokinetic modeling.

To be analyzed, the heterogeneity characterizing biological data calls for using appropriate models involving numerous variables. A high variable number could become problematic when one needs to determine a priori the most significant variable combination in order to reduce the inter-individual variability (IIV). Alternatively to multiple introductions of single variables, we propose a single introduction of a multivariate variable. We present cluster analysis as a stratification strategy that combines the initial single covariates to build a multivariate categorical covariate. It is an exploratory multivariate analysis that outlines homogeneous categories of individuals (clusters) according to similarities from the set of covariates. It includes many clustering techniques combining a distance measure and a linkage algorithm, and leading to various stratification patterns. The cluster analysis approach is illustrated by a case study on cortisol kinetics in 82 patients after intravenous bolus administration of synacthen (synthetic corticotropin). Using NONMEM, a basic infusion model was initially achieved for cortisol, and then a classical covariate selection was applied to improve IIV. The best fit was between the elimination rate constant k and the body mass index (BMI), which improved IIV of k. An alternative method is presented consisting in the population into homogeneous and non-overlapping groups by applying a cluster analysis. Such categorization (or clustering) was carried out using Euclidean distance and complete-linkage algorithm. This algorithm gave five dissimilar clusters that differed by increasing BMI, obesity duration, and waist-hip ratio. The dispersion of k according to the five clusters showed three distinctvariation ranges a priori, which corresponded a posteriori(after NONMEM modeling) to three sub-populations of k. After grouping the clusters that had similar variation ranges of k, we obtained three final clusters representing non-obese, intermediate, and extreme obese sub-populations. The pharmacokinetic model based on three clusters was better than the basic model, similar to the classical covariate model, but had a stronger interpretability: It showed that the stimulation and elimination of cortisol were higher in the extreme obese followed by intermediate then non-obese subjects.

Adrenocorticotropic Hormone↗

The effects of a normal protein diet on levodopa plasma kinetics in advanced Parkinson's disease.

LevoDOPA given orally may compete with the neutral aminoacids contained in food for its absorption in the small intestine. LevoDOPA plasma kinetics of the morning intake with 'french' breakfast (low protein content) were compared with those of the noon intake with lunch (normal protein content) in 20 advanced parkinsonian patients (mean disease duration: 10 years). The galenic form and the dosage of levoDOPA were strictly the same for morning and noon intakes in each patient. Blood samplings were collected at T0 (just before intake) and successively at 15, 30, 45, 60, 90, 120, 150 and 180 min after intake. LevoDOPA plasma levels were further measured with HPLC method, then giving the following variables: Cmax (peak concentration), Tmax (time corresponding to Cmax), AUC (area under curve). The results showed no significant difference for Cmax and Tmax whereas the AUC was significantly (P < 0.001) increased for the noon intake, due to the trough concentration effect. These data suggest that, since rich protein diet has been shown to impair the clinical effect of LevoDOPA, this protein effect is probably not due to competitive intestinal absorption of LevoDOPA.

Adult↗

Population pharmacokinetics of moxifloxacin in plasma and bronchial secretions in patients with severe bronchopneumonia.

OBJECTIVE: Our objective was to construct a population pharmacokinetic model for moxifloxacin disposition in plasma and bronchial secretions in patients with severe bronchopneumonia who were mechanically ventilated. METHODS: Seventeen patients receiving 400 mg moxifloxacin intravenously daily were enrolled in this multicenter, prospective, open-label study. Blood and bronchial samples were collected on days 1 and 4. The population pharmacokinetic modeling was performed with NONMEM. RESULTS: Moxifloxacin rapidly appeared in bronchial secretions and reached maximum concentrations within 1 to 2 hours. The concentrations achieved in plasma and bronchial secretions showed parallel profiles versus time on days 1 and 4. The pharmacokinetics was best described by a 2-compartment model with a link to bronchial secretions. The population pharmacokinetic parameters were as follows (given as estimate with percent interindividual variability in parentheses except where otherwise indicated): clearance, 14.3 L/h (25%); central distribution volume, 62.9 L (14%); intercompartmental clearance, 27.2 L/h (36%); peripheral distribution volume; 71 L (32%); fraction of moxifloxacin clearance to bronchial secretions, 0.11 (range, 0.06-0.16); and elimination rate constant for bronchial secretions, 1.7 h(-1) (40%). The plasma terminal half-life was 6.7 hours. The bronchial-to-plasma exposure ratio was 1.0 (range, 0.6-2.0). With a conservative 90% minimum inhibitory concentration (MIC(90)) of 0.25 mg/L, the maximum concentration/MIC(90) ratios were higher than 10 and the area under the curve/MIC(90) ratios were roughly 100 for plasma and bronchial secretions. CONCLUSIONS: This study showed the fast diffusion of moxifloxacin into the lungs in ventilated patients with severe respiratory infection. The bronchial secretions reached bactericidal levels for common germs found in respiratory tract infections.

Adult↗

Tacrolimus and sirolimus decrease oxidative phosphorylation of isolated rat kidney mitochondria.

1. Tacrolimus and sirolimus are potent immunosuppressors used in transplantation. Tacrolimus has been suspected to alter mitochondrial respiration of different tissues but sirolimus has not been evaluated. 2. We evaluated the in vitro effect of tacrolimus and sirolimus on oxidative phosphorylation of isolated rat kidney mitochondria. 3. Oxygen consumption was measured with a Clark-type electrode. Tacrolimus and sirolimus increased the resting rate (state 4) and had no significant effect on ADP-stimulated respiration (state 3). The decrease of respiratory control ratio was concentration-dependent with a biphasic curve for tacrolimus. The EC(50)s were 3.4 x 10(-11) M and 2.3 x 10(-8) M for tacrolimus and 4.4 x 10(-10) M for sirolimus. The maximal inhibition was 20 and 14% for tacrolimus and sirolimus, respectively. 4. Tacrolimus and sirolimus had an uncoupling effect on oxidative phosphorylation related to a decrease of the inner membrane fluidity. At the opposite of cyclosporin A, no effect on swelling or Ca(2+) fluxes was observed. 5. All events occurred at therapeutic concentrations and then could appear during long-term treatment. Cellular consequences such as chronic nephrotoxicity with tacrolimus are suggested. The risk of cyclosporin A nephrotoxicity potentiation by sirolimus is discussed.

Animals↗

Circadian rhythms of oxidative phosphorylation: effects of rotenone and melatonin on isolated rat brain mitochondria.

Mitochondrial experiments are of increasing interest in different fields of research. Inhibition of mitochondrian activities seems to play a role in Parkinson's disease and in this regard several animal models have used inhibitors of mitochondrial respiration such as rotenone or MPTP. Most of these experiments were done during the daytime. However, there is no reason for mitochondrial respiration to be constant during the 24 h. This study investigated the circadian variation of oxidative phosphorylation in isolated rat brain mitochondria and the administration-time-dependent effect of rotenone and melatonin. The respiratory control ratio, state 3 and state 4, displayed a circadian fluctuation. The highest respiratory control ratio value (3.01) occurred at 04:00 h, and the lowest value (2.63) at 08:00 h. The highest value of state 3 and state 4 oxidative respiration occurred at 12:00 h and the lowest one at 20:00 h. The 24 h mean decrease in the respiratory control ratio following incubation with melatonin and rotenone was 7 and 32%, respectively; however, the exact amount of the inhibition exerted by these agents varied according to the time of the mitochondria isolation. Our results show the time of mitochondrial isolation could lead to interindividual variability. When studies require mitochondrial isolation from several animals, the time between animal experiments has to be minimized. In oxidative phosphorylation studies, the time of mitochondria isolation must be taken into account, or at least specified in the methods section.

Animals↗

Pharmacokinetics of the low molecular weight heparin enoxaparin during 48 h after bolus administration as an anticoagulant in haemodialysis.

BACKGROUND: The interest of low molecular weight heparins (LMWH) regarding bleeding risk is controversial in renal failure patients. In haemodialysis patients, there are very few data on the pharmacokinetics of LMWH after the end of the session. The aim of the study was to evaluate the duration of anticoagulation after bolus administration of the LMWH enoxaparin at the start of haemodialysis. METHODS: The pharmacokinetics of enoxaparin were studied during the 48 h following a single bolus injection at the start of the dialysis session in 30 chronic haemodialysis patients. Pharmacokinetics were determined using a population approach (Non Linear Mixed Effects Modelling). RESULTS: A single injection of enoxaparin at 60 U IU/kg (4000 +/- 455 IU) led to an anti-Xa activity higher than 1.2 IU/ml during the first 2 h of the session, and between 0.4 and 1.2 IU during the third and fourth hours. After the end of the session, anti-Xa activity remained higher than 0.4 IU/ml up to 10 h after injection, and higher than 0.1 IU/ml up to 24 h. The pharmacokinetic model showed that only weight improved the predicted vs observed anti-Xa activity plot. The model was used to simulate single and multiple dosing with decreased enoxaparin doses. Whatever the procedure, anti-Xa activity remained high (>0.22 +/- 0.99 UI/ml) up to 12 h after the start of the dialysis session. CONCLUSIONS: These results suggest that haemodialysis patients receiving the LMWH enoxaparin during dialysis are at risk of bleeding up to 10 h after the injection.

Adult↗

Performance of target-controlled sufentanil infusion in obese patients.

BACKGROUND: Because obesity might affect pharmacokinetic parameters, the authors evaluated the accuracy of target-controlled sufentanil infusion in morbidly obese patients using a pharmacokinetic model usually applied to a normal-weight population. METHODS: Target-controlled propofol and sufentanil coinfusions were administered to 11 morbidly obese patients (body mass index: 45.0 +/- 6.5 kg/m2 ) undergoing laparoscopic gastroplasty. The target plasma propofol concentration was 3 micro g/ml. The effect-site sufentanil target concentration was initially 0.4 ng/ml but was modified during surgery as a function of blood pressure and heart rate. Plasma sufentanil concentrations were measured from the onset of infusion until 24 h after its termination. The predicted sufentanil target concentrations were calculated by STANPUMP software. Intrasubject data analyzed included calculation of performance error, median performance error, median absolute performance error, divergence, and wobble. Pharmacokinetic analysis was performed using a nonlinear mixed effect model. RESULTS: Applied sufentanil target concentrations ranged from 0.3 to 0.65 ng/ml. The mean +/- SD plasma sufentanil concentration measured during spontaneous ventilation was 0.13 +/- 0.03 ng/ml. Median performance error (range) was -13% (-42 to 36%). Median absolute performance error was 26% (8-44%) during infusion and 17% (12-59%) for the 24 h after its completion. The pharmacokinetic sets used slightly overpredicted the concentrations, with a median divergence of -3.4% (-10.2 to 3.1%) during infusion. For body mass index greater than 40, the overestimation of plasma sufentanil concentrations was greater. A two-compartment model with proportional error for interindividual variability best fitted the data. The residual variability was modeled as an additive (0.016 ng/ml) or proportional error (23%). Clearance, central volume of distribution, intercompartmental clearance, and peripheral volume of distribution (coefficient of variation) were 1.27 l/min (23%), 37.1 l (20%), 0.87 l/min (44%), and 92.7 l (22%), respectively. CONCLUSION: The pharmacokinetic parameter set derived from a normal-weight population accurately predicted plasma sufentanil concentrations in morbidly obese patients.

Adolescent↗

Time-of-day dependent pharmacodynamic and pharmacokinetic profiles of caffeine in rats.

This study aims to investigate the effects of caffeine on the daily rhythms of heart rate (HR), body temperature (BT) and locomotor activity (LA) in rats in relation to time-of-day of administration, as well as their possible mechanisms, particularly related to caffeine pharmacokinetics. During the pharmacodynamic study, HR, BT and LA were measured every 10 min by radiotelemetry and analysed by Cosinor. This study was divided into three periods: a control period P1, a treatment period P2 and a recovery period P3. During P2, rats of the morning group ( M(tel)) received a 25 mg/kg s.c. dose of caffeine at 08.00 while rats of the evening group ( E(tel)) received the same dose of caffeine at 20.00. The pharmacokinetic study was conducted in parallel with the telemetric study and was divided into two periods: a control period P1, and a treatment period P2. During P2, animals of the morning ( M(pk)) and the evening ( E(pk)) groups received the same treatment as the animals of the telemetric study. At the last day of P2, blood samples were drawn 0.25, 0.5, 1, 2, 4, 8, 12 and 24 h after the last morning and the last evening administration in order to determine the pharmacokinetics of M(pk) and E(pk). Our results showed that morning administration of caffeine suppressed the daily rhythmicity of LA and modified the mesors and amplitudes of the HR and BT daily rhythms, while the evening administration did not suppress the daily rhythm of LA, but altered the mesors, amplitudes and acrophases of the three rhythms, indicating a chronopharmacological effect. With respect to the pharmacokinetic effects, the area under the curve (AUC) was significantly lower in rats of E(pk) compared with M(pk), due to an increase of the total plasma clearance and the volume of distribution. Our data suggest that the chronopharmacokinetic effects of caffeine may explain, at least in part, the observed caffeine-induced modifications on the daily rhythms.

Animals↗

Biologic rhythms and Parkinson's disease: a chronopharmacologic approach to considering fluctuations in function.

The existence of circadian rhythms and their implication in many pathologic processes have been underlined in several diseases but have not been evaluated in Parkinson's disease. The aim of this paper is to review diurnal variations of clinical, biologic, or experimental factors described with Parkinson's disease. Clinical data often report daily fluctuations of motor activity pattern, but the effect of the stage of the disease and the respective roles of drugs are difficult to evaluate. Sleep disturbances in Parkinson's disease patients also reveal alterations of circadian rhythms. Autonomic dysfunction, described in Parkinson's disease, reveals numerous alterations in circadian regulations including loss of circadian rhythm of blood pressure, increased diurnal blood pressure variability, and postprandial hypotension. Many biologic indices such as cortisol, catecholamines, and melatonin are also altered. Circadian rhythms in dopaminergic systems as well as possible daily fluctuations in kinetics of drug treatments are likely involved in such variations. Few clinical studies have been devoted to circadian patterns of drug response. As for other diseases where biologic rhythms are concerned Parkinson's disease therapy may be influenced by further understanding of circadian influence.

Animals↗

[Involvement of a public pharmacology laboratory in pharmacokinetic studies].

Pharmacokinetic studies can be performed before or after a drug is marketed. Indeed, extensive use of a new drug can uncover situations that it has not been possible to investigate before market application. Hospital departments of pharmacology are often involved in these complementary studies. They can design the study, initiate it in a clinical investigation centre, measure plasma concentrations, analyse the pharmacokinetic data, and write the report. If the extent of the scientific involvement of public pharmacology laboratories is strictly demarcated, financial support for nonsponsored studies by the pharmaceutical industry is problematical. Indeed, it is difficult to obtain funds to study the concentration-toxicity relationship or a drug-drug interaction for a compound for which the patent has expired. In addition, such studies have an excess cost, mainly because of the expense associated with drug measurements. Also, the medical time devoted to research is not rewarded by institutions. This situation will become more complicated because of the restrictive legislative framework imposed by the European directive.

Laboratories, Hospital↗