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Dive into the research topics where William Couet is active.

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Featured researches published by William Couet.


Pharmaceutical Research | 1999

Indirect evidence that drug brain targeting using polysorbate 80-coated polybutylcyanoacrylate nanoparticles is related to toxicity.

Jean-Christophe Olivier; Laurence Fenart; Romain Chauvet; Claudine Pariat; Roméo Cecchelli; William Couet

AbstractPurpose. To investigate the mechanism underlying the entry of the analgesic peptide dalargin into brain using biodegradable polybutylcyanoacrylate (PBCA) nanoparticles (NP) overcoated with polysorbate 80. Methods. The investigations were carried out with PBCA NP and with non biodegradable polystyrene (PS) NP (200 nm diameter). Dalargin adsorption was assessed by HPLC. Its entry into the CNS in mice was evaluated using the tail-flick procedure. Locomotor activity measurements were performed to compare NP toxicities. BBB permeabilization by PBCA NP was studied in vitro using a coculture of bovine brain capillary endothelial cells and rat astrocytes. Results. Dalargin loading was 11.7 µg/mg on PBCA NP and 16.5µg/ mg on PS NP. Adding polysorbate 80 to NP led to a complete desorption. Nevertheless, dalargin associated with PBCA NP and polysorbate 80 induced a potent and prolonged analgesia, which could not be obtained using PS NP in place of PBCA NP. Locomotor activity dramatically decreased in mice dosed with PBCA NP, but not with PS NP. PBCA NP also caused occasional mortality. In vitro, PBCA NP (10 µg/ml) induced a permeabilization of the BBB model. Conclusions. A non specific permeabilization of the BBB, probably related to the toxicity of the carrier, may account for the CNS penetration of dalargin associated with PBCA NP and polysorbate 80.


Lancet Infectious Diseases | 2015

Framework for optimisation of the clinical use of colistin and polymyxin B: the Prato polymyxin consensus.

Roger L. Nation; Jian Li; Otto Cars; William Couet; Michael N. Dudley; Keith S. Kaye; Johan W. Mouton; David L. Paterson; Vincent H. Tam; Ursula Theuretzbacher; Brian T. Tsuji; John Turnidge

In the face of diminishing therapeutic options for the treatment of infections caused by multidrug-resistant, Gram-negative bacteria, clinicians are increasingly using colistin and polymyxin B. These antibiotics became available clinically in the 1950s, when understanding of antimicrobial pharmacology and regulatory requirements for approval of drugs was substantially less than today. At the 1st International Conference on Polymyxins in Prato, Italy, 2013, participants discussed a set of key objectives that were developed to explore the factors affecting the safe and effective use of polymyxins, identify the gaps in knowledge, and set priorities for future research. Participants identified several factors that affect the optimum use of polymyxins, including: confusion caused by several different conventions used to describe doses of colistin; an absence of appropriate pharmacopoeial standards for polymyxins; outdated and diverse product information; and uncertainties about susceptibility testing and breakpoints. High-priority areas for research included: better definition of the effectiveness of polymyxin-based combination therapy compared with monotherapy via well designed, randomised controlled trials; examination of the relative merits of colistin versus polymyxin B for various types of infection; investigation of pharmacokinetics in special patient populations; and definition of the role of nebulised polymyxins alone or in combination with intravenous polymyxins for the treatment of pneumonia. The key areas identified provide a roadmap for action regarding the continued use of polymyxins, and are intended to help with the effective and safe use of these important, last-line antibiotics.


European Journal of Pharmaceutical Sciences | 2000

In vitro and in vivo investigations on fluoroquinolones; effects of the P-glycoprotein efflux transporter on brain distribution of sparfloxacin.

Elizabeth C.M. de Lange; Sandrine Marchand; Dirk-Jan van den Berg; Inez C.J van der Sandt; Albertus G. de Boer; Annie Delon; Serge Bouquet; William Couet

The role of mdr1a-encoded P-glycoprotein on transport of several fluoroquinolones across the blood-brain barrier was investigated. In vitro, P-glycoprotein substrates were selected by using a confluent monolayer of MDR1-LLC-PK1 cells. The inhibition of fluoroquinolones (100 microM) on transport of rhodamine-123 (1 microM) was compared with P-glycoprotein inhibitors verapamil (20 microM) and SDZ PSC 833 (2 microM). Subsequently, transport polarity of fluoroquinolones was studied. Sparfloxacin showed the strongest inhibition (26%) and a large polarity in transport, by P-glycoprotein activity. In vivo, using mdr1a (-/-) and wild-type mice, brain distribution of pefloxacin, norfloxacin, ciprofloxacin, fleroxacin and sparfloxacin was determined at 2, 4, and 6 h following intra-arterial infusion (50 nmol/min). Brain distribution of sparfloxacin was clearly higher in mdr1a (-/-) mice compared with wild-type mice. Sparfloxacin was infused (50 nmol/min) for 1, 2, 3 and 4 h in which intracerebral microdialysis was performed. At 4 h, in vivo recovery (dynamic-no-net-flux method) was 6.5+/-2.2 and 1.5+/-0.5%; brain(ECF) concentrations were 5.1+/-0.2 and 26+/-21 microM; and total brain concentrations were 7.2+/-0.3 and 23+/-0.3 microM in wild-type and mdr1a (-/-) mice, respectively. Plasma concentrations were similar (18.4+/-0.7 and 17.9+/-0.5 microM, respectively). In conclusion, sparfloxacin enters the brain poorly mainly because of P-glycoprotein activity at the blood-brain barrier.


Pharmaceutical Research | 2004

Anticancer Drug Delivery with Transferrin Targeted Polymeric Chitosan Vesicles

Christine Dufès; Jean-Marc Muller; William Couet; Jean-Christophe Olivier; Ijeoma F. Uchegbu; Andreas G. Schätzlein

AbstractPurpose. The study reports the initial biological evaluation of targeted polymeric glycol chitosan vesicles as carrier systems for doxorubicin (Dox). Methods. Transferrin (Tf) was covalently bound to the Dox-loaded palmitoylated glycol chitosan (GCP) vesicles using dimethylsuber- imidate (DMSI). For comparison, glucose targeted niosomes were prepared using N-palmitoyl glucosamine. Biological properties were studied using confocal microscopy, flow cytometry, and cytotoxicity assays as well as a mouse xenograft model. Results. Tf vesicles were taken up rapidly with a plateau after 1-2 h and Dox reached the nucleus after 60-90 min. Uptake was not increased with the use of glucose ligands, but higher uptake and increased cytotoxicity were observed for Tf targeted as compared to GCP Dox alone. In the drug-resistant A2780AD cells and in A431 cells, the relative increase in activity was significantly higher for the Tf-GCP vesicles than would have been expected from the uptake studies. All vesicle formulations had a superior in vivo safety profile compared to the free drug. Conclusions. The in vitro advantage of targeted Tf vesicles did not translate into a therapeutic advantage in vivo. All vesicles reduced tumor size on day 2 but were overall less active than the free drug.


International Journal of Pharmaceutics | 2003

Brain delivery of vasoactive intestinal peptide (VIP) following nasal administration to rats

Christine Dufès; Jean-Christophe Olivier; Frederic Gaillard; Afsaneh Gaillard; William Couet; Jean-Marc Muller

The aim of this work was to study in rats the nasal route for the brain delivery of the vasoactive intestinal peptide (VIP) neuropeptide. After evaluating VIP stability in solutions obtained from nasal washes, the effect of formulation parameters (pH 4-9, 0-1% (w/v) lauroylcarnitine (LC), hypo- or isoosmolality) on the brain uptake of intranasally administered VIP (10(-8)M)/125I-VIP (300,000 cpm/ml) was studied, using an in situ perfusion technique. Brain radioactivity distribution was assessed by quantitative autoradiographic analysis. Results were compared to intravenously administered VIP. With a hypotonic formulation at pH 4 containing 0.1% LC and 1% bovine serum albumin, VIP stability was satisfactory and loss by adsorption was minimal. Using this formulation, around 0.11% of initial radioactivity was found in the brain after 30 min perfusion and was located in the olfactory bulbs, the midbrain and the cerebellum. HPLC analysis of brain and blood extracts demonstrated the presence of intact VIP in brain and its complete degradation in the blood compartment. By intravenous administration, no intact VIP was found either in brain or in blood. In conclusion, intact VIP could be delivered successfully to the brain using the intranasal route for administration.


Clinical Microbiology and Infection | 2012

Colistin pharmacokinetics: the fog is lifting

William Couet; Nicolas Grégoire; Sandrine Marchand; Olivier Mimoz

Colistin is a re-emerging old antibiotic that is used to treat multidrug-resistant infections in critically ill patients. It corresponds to a mixture of at least 30 different compounds administered as inactive derivatives. Therefore, colistin pharmacokinetics are quite difficult to investigate and complex to predict. However specific chromatographic methods have been made available in recent years, leading to a series of modern pharmacokinetic studies after intravenous administration of the prodrug to critical-care patients; these have been conducted by a few groups and have only been recently published. The objective of this article was to conduct a critical review of these very informative modern pharmacokinetic studies and to provide prospective thoughts.


Antimicrobial Agents and Chemotherapy | 2010

Assay of Colistin and Colistin Methanesulfonate in Plasma and Urine by Liquid Chromatography-Tandem Mass Spectrometry

Patrice Gobin; Florian Lemaitre; Sandrine Marchand; William Couet; Jean-Christophe Olivier

ABSTRACT A rapid high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed for the routine quantification of colistins A and B and their prodrugs, colistin methanesulfonate (CMS) A and CMS B, respectively, in human plasma and urine by using polymyxin B1 as the internal standard (IS). CMS concentrations were determined indirectly by subtracting the colistin concentrations determined in biological samples from the whole colistin concentrations determined after sample treatment with sulfuric acid in order to hydrolyze CMS into colistin. After extraction on a solid-phase extraction column, the colistins were separated on an XBrigde C18 column with isocratic elution (run time, 3.8 min). The mobile phase was 0.1% (vol/vol) formic acid in acetonitrile-0.1% (vol/vol) formic acid in water (20:80, vol/vol), run at a 0.2-ml/min flow rate. Ions were detected in the turbo-ion-spray-positive and multiple-reaction-monitoring modes. The ions monitored (precursor [M + 2H]2+ to product ions) were m/z 585.5/101.2 for colistin A, m/z 578.5/101.2 for colistin B, and m/z 602.5/241.2 for IS. Prevalidation studies demonstrated the stability of CMS in biological samples and extracts, a key point for the reliable quantification of colistin and CMS. The assay was accurate and reproducible for the quantification of colistins A and B and CMSs A and B in plasma samples over concentration ranges appropriate for pharmacokinetic studies: 0.024 to 6.144, 0.015 to 3.856, 0.029 to 7.492, and 0.010 to 2.508 μg/ml, respectively. In urine samples, the assay was validated over the same concentration ranges for colistins and over concentration ranges of 0.058 to 7.492 μg/ml and 0.020 to 2.508 μg/ml for CMSs A and B, respectively.


Pharmaceutical Research | 2000

Niosomes and polymeric chitosan based vesicles bearing transferrin and glucose ligands for drug targeting

Christine Dufès; Andreas G. Schätzlein; Laurence Tetley; Alexander I. Gray; Dave G. Watson; Jean-Christophe Olivier; William Couet; Ijeoma F. Uchegbu

AbstractPurpose. To prepare polymeric vesicles and niosomes bearing glucose or transferrin ligands for drug targeting. Methods. A glucose-palmitoyl glycol chitosan (PGC) conjugate was synthesised and glucose-PGC polymeric vesicles prepared by sonication of glucose-PGC/ cholesterol. N-palmitoylglucosamine (NPG) was synthesised and NPG niosomes also prepared by sonication of NPG/ sorbitan monostearate/ cholesterol/ cholesteryl poly-24-oxyethylene ether. These 2 glucose vesicles were incubated with colloidal concanavalin A gold (Con-A gold), washed and visualised by transmission electron microscopy (TEM). Transferrin was also conjugated to the surface of PGC vesicles and the uptake of these vesicles investigated in the A431 cell line (over expressing the transferrin receptor) by fluorescent activated cell sorter analysis. Results. TEM imaging confirmed the presence of glucose units on the surface of PGC polymeric vesicles and NPG niosomes. Transferrin was coupled to PGC vesicles at a level of 0.60 ± 0.18 g of transferrin per g polymer. The proportion of FITC-dextran positive A431 cells was 42% (FITC-dextran solution), 74% (plain vesicles) and 90% (transferrin vesicles). Conclusions. Glucose and transferrin bearing chitosan based vesicles and glucose niosomes have been prepared. Glucose bearing vesicles bind Con-A to their surface. Chitosan based vesicles are taken up by A431 cells and transferrin enhances this uptake.


Journal of Controlled Release | 2008

Formulation of rifampicin–cyclodextrin complexes for lung nebulization

Frederic Tewes; Julien Brillault; William Couet; Jean–Christophe Olivier

Lung administration of antibiotics by nebulization is promising for improving treatment efficiency for pulmonary infections, as it increases drug concentration at sites of infection while minimizing systemic side effects. For poorly soluble molecules like rifampicin, cyclodextrins (CD) may improve lung delivery by permitting higher dosing. For this purpose, we investigated rifampicin-CD complexes in terms of rifampicin apparent solubility enhancement, effect on in vitro permeability on Calu-3 broncho-alveolar cells, effect on in vitro antibacterial activity against Acinetobacter baumannii and nebulization characteristics measured by NGI cascade impactor. Complexation efficiency between rifampicin and methylated beta-cyclodextrin (RAMEB) or hydroxypropyl-beta-cyclodextrin (HPbetaCD) was pH-dependent, involving the piperazin group. Rifampicin phase solubility diagrams constructed at pH 9 showed an A(L)-type curve for RAMEB and a B(S)-type for HPbetaCD. Stability constants calculated for a 1:1 molar ratio of CD/rifampicin were 73.4 +/- 8.2 M(-1) for RAMEB and 68.5 +/- 5.2 M(-1) for HPbetaCD. Complexes with RAMEB or HPbetaCD increased 22 times and 7.6 times respectively the apparent solubility of rifampicin and were found to be satisfactorily stable for 2 days when diluted in a solution at physiological pH. The nebulization of the complex solution created droplets in size range compatible with pulmonary deposition. Furthermore, the presence of HPbetaCD decreased the MMAD of the aerosolized droplets. Activity of RAMEB and HPbetaCD complexes measured by the total rifampicin MIC against A. baumannii was similar or lower to free rifampicin MIC respectively. Complexation did not alter the rifampicin permeability in the timescale of 1h as evaluated with a Calu-3 epithelial cell model, but acted as a reservoir for rifampicin. In conclusion, this work reports that CDs can be used as vectors for pulmonary nebulization to increase the amount of active rifampicin and optimize its lung pharmacokinetic profile.


Clinical Pharmacology & Therapeutics | 2008

Pharmacokinetics of Meropenem Determined by Microdialysis in the Peritoneal Fluid of Patients With Severe Peritonitis Associated With Septic Shock

J Karjagin; S Lefeuvre; K Oselin; Karin Kipper; Sandrine Marchand; A Tikkerberi; J Starkopf; William Couet; Ronald J. Sawchuk

Our objective was to describe the pharmacokinetics of meropenem in the peritoneal fluid (PF) of six patients with severe peritonitis and septic shock and to relate measured concentrations to the minimum inhibitory concentration of bacteria. Microdialysis catheters were placed into the peritoneal space during surgery. Meropenem concentrations in plasma and in PF were analyzed using compartmental modeling. Meropenem areas under the concentration–time curve were lower in PF than in plasma (average ratio, 73.8±15%) because of degradation confirmed ex vivo. Compartment modeling with elimination from a peripheral compartment described the data adequately, and was used to simulate steady‐state concentration profiles in plasma and PF during various dosing regimens. At the currently recommended dosing regimen of 1 g infused over 20 min every 8 h, PF concentrations of meropenem in patients with severe peritonitis associated with septic shock reach values sufficient for antibacterial effects against susceptible, but not always against intermediately susceptible, bacteria.

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