In Vivo Methods for the Assessment of Topical Drug Bioavailability

This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application. After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies. Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also describe

In Vivo Methods for the Assessment of Topical Drug Bioavailability

This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application. After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies. Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also described

Clinical and molecular epidemiological features of critically ill patients with invasive group A Streptococcus infections: a Belgian multicenter case-series.

peer reviewed[en] BACKGROUND: Recent alerts have highlighted an increase in group A streptococcal (GAS) infections since 2022 in Europe and the United States. Streptococcus pyogenes can cause limited skin or mucosal disease, but can also present as severe invasive disease necessitating critical care. We performed a multicenter retrospective study of patients with GAS infections recently admitted to Belgian intensive care units (ICUs) since January 2022. We describe patient characteristics and investigate the molecular epidemiology of the S. pyogenes strains involved. RESULTS: Between January 2022 and May 2023, a total of 86 cases (56 adults, 30 children) with GAS disease were admitted to critical care in the university hospitals of Leuven, Antwerp and Liège. We noted a strikingly high incidence of severe community-acquired pneumonia (sCAP) (45% of adults, 77% of children) complicated with empyema in 45% and 83% of adult and pediatric cases, respectively. Two-thirds of patients with S. pyogenes pneumonia had viral co-infection, with influenza (13 adults, 5 children) predominating. Other disease presentations included necrotizing fasciitis (23% of adults), other severe skin/soft tissue infections (16% of adults, 13% of children) and ear/nose/throat infections (13% of adults, 13% of children). Cardiogenic shock was frequent (36% of adults, 20% of children). Fifty-six patients (65%) had toxic shock syndrome. Organ support requirements were high and included invasive mechanical ventilation (77% of adults, 50% of children), renal replacement therapy (29% of adults, 3% of children) and extracorporeal membrane oxygenation (20% of adults, 7% of children). Mortality was 21% in adults and 3% in children. Genomic analysis of S. pyogenes strains from 55 out of 86 patients showed a predominance of emm1 strains (73%), with a replacement of the M1global lineage by the toxigenic M1UK lineage (83% of emm1 strains were M1UK). CONCLUSIONS: The recent rise of severe GAS infections (2022-23) is associated with introduction of the M1UK lineage in Belgium, but other factors may be at play-including intense circulation of respiratory viruses and potentially an immune debt after the COVID pandemic. Importantly, critical care physicians should include S. pyogenes as causative pathogen in the differential diagnosis of sCAP

Development of the cutaneous and subcutaneous microdialysis sampling technique for distribution studies of drug administered by different routes

Etant le plus grand organe du corps, à la fois par le poids et la surface, la peau est un important compartiment corporel à prendre en considération dans l'étude de la distribution des médicaments après administration systémique. Elle constitue également une grande surface facilement accessible pour l'administration de médicaments. Dès lors, le développement et l'évaluation des médicaments administrés par voie topique et transdermique nécessite la détermination in vivo des concentrations du médicaments dans la peau. L'objectif de ce travail était de développer la technique de microdialyse cutanée et sous-cutanée pour l'étude de la pénétration des médicaments dans la peau après administration systémique ou topique. L'utilisation des techniques biophysiques non invasives en association avec une étude histologique nous ont montré que l'implantation cutanée et sous-cutanée des sondes linéaires de microdialyse ne modifiait ni le débit sanguin cutané ni la fonction barrière de la peau. Ces résultats ont confirmé que la technique de microdialyse est bien tolérée dans l'étude de la dermatopharmacocinétique des médicaments après administration topique ou systémique. Dans le cas des infections fongiques cutanées, la détermination des concentrations d'antifongiques dans la peau est bien plus pertinente que la mesure des concentrations plasmatiques dans la détermination de l'efficacité antifongique. Dans ce travail, nous avons développé avec succès un double échantillonnage par microdialyse couplé à l'HPLC microbore pour étudier la pénétration du fluconazole dans la peau. Après administration intraveineuse sous forme de bolus, le fluconazole pénètre rapidement dans le derme où les concentrations libres mesurées furent similaires à celles observées dans le plasma par microdialyse sanguine. Pour le traitement des infections fongiques superficielles et localisées, le fluconazole est disponible sous forme de gel pour application topique. Notre étude est la première dans laquelle la pénétration cutanée du fluconazole après application topique a été étudiée par microdialyse dermique. Nous avons ainsi montré que des concentrations thérapeutiques de fluconazole étaient obtenues après application dermique du Diflucan gel. La microdialyse cutanée nous a permis de caractériser avec une grande résolution temporelle la pénétration cutanée du fluconazole. Parce que seule la fraction libre des médicaments traverse la membrane de dialyse, nous avons démontré, en utilisant le flurbiprofen comme molécule modèle, que la microdialyse sous-cutanée est un outil intéressant pour l'étude de la pharmacocinétique et la détermination in vivo de la liaison des médicaments aux protéines chez le rat. Dans le cadre de l'administration transdermique des médicaments par iontophorèse, la plupart des données ont été obtenues in vitro en utilisant les cellules de diffusion. Parce que la microdialyse est particulièrement efficace pour l'échantillonnage des molécules hydrosolubles, cette technique apparaît intéressante pour étudier l'administration des médicaments par iontophorèse. Le présent travail est la première étude in vivo dans laquelle une double échantillonnage par microdialyse est utilisé pour étudier la pénétration percutanée du flurbiprofen après administration par iontophorèse. En mesurant simultanément les concentrations libres de flurbiprofen dans le derme et dans le tissu sous-cutané sous le site d'application, nous avons pu mettre en évidence un important gradient de concentrations dans le tissu. En effet, les concentrations libres de flurbiprofen dans le derme furent 10 fois plus grandes que les concentrations libres dans le tissu sous-cutané. Ceci suggère que le derme doit être considéré comme un compartiment corporel distinct où les concentrations libres de flurbiprofen ne sont pas en équilibres avec celle du tissu sous-cutané. Parmi les méthodes dermatopharmacocinétiques, la microdialyse cutanée est une technique d'échantillonnage continu permettant une complète caractérisation des profiles concentrations-temps avec une haute résolution temporelle. Ces caractéristiques sont particulièrement intéressantes pour étudier avec une chronologie détaillée la vitesse et le degré avec lesquels le médicament devient disponible au site d'action, à savoir la peau, après administration topique ou systémique.Being the largest organ of the body, both by weight and by surface area, the skin is an important body compartment to take into account when considering the distribution study of drugs following systemic administration. The skin presents also a readily accessible surface area for drug administration. Hence, the development and the evaluation of dermal and transdermal drug delivery require the in vivo measurement of drug concentrations in the skin. The aim of this thesis was to develop the cutaneous and subcutaneous microdialysis sampling technique to study the skin penetration of drugs following systemic and topical administration. By using non-invasive bioengineering techniques combined with histological studies, we have shown that the dermal and subcutaneous insertion of linear microdialysis probes did induce neither modification of cutaneous blood flow nor impairment of the skin barrier function. These results confirmed that the microdialysis technique is safe to study the dermatopharmacokinetics after topical or systemic administration. In the case of cutaneous fungal infections, measurements of antifungal concentrations in the skin are more relevant than plasma concentrations in understanding their antifungal efficacy. In the present work, on-line microdialysis using dual-site sampling coupled with microbore HPLC system was successfully applied to investigate the penetration of fluconazole in the rat skin. Following intravenous bolus injection, fluconazole rapidly penetrates into the dermis where the unbound concentrations were very similar to those measured in plasma by vascular microdialysis. For the treatment of superficial and localized fungal infections of the skin, fluconazole was formulated for topical application as a gel. Our study is the first in which cutaneous penetration of fluconazole after topical application was investigated by dermal microdialysis. Our results show that therapeutic concentrations of fluconazole are achieved following topical application of Diflucan Gel. Cutaneous microdialysis allowed us to characterize the skin penetration of fluconazole with a high temporal resolution. Because only unbound drug molecules pass through the dialysis membrane, microdialysis is also a useful tool to study in vivo the protein binding of drugs. By using flurbiprofen as a model molecule, we have demonstrated that subcutaneous microdialysis is a powerful tool to study the pharmacokinetics and the in vivo protein binding of drug in the awake unrestrained rat. In the area of transdermal drug delivery by iontophoresis, most of the data on percutaneous penetration have been gained in vitro by using diffusion chamber experiments. As microdialysis was shown to be especially efficient in sampling water soluble molecules with a minimum induced trauma, the technique appears particularly suitable to study iontophoresis that delivers ions or highly polar drugs. The present work is the first in vivo study where an on-line dual-site sampling by microdialysis was used to investigate the percutaneous penetration of flurbiprofen following iontophoretic delivery. By measuring simultaneously the unbound flurbiprofen concentrations in dermis and in subcutaneous tissue below the application site, an important gradient in tissue concentrations of flurbiprofen was observed. Unbound concentrations of flurbiprofen in dermis were 10-fold higher than unbound concentrations in subcutaneous tissue. These results suggest that dermis must be considered as a distinct body compartment where unbound flurbiprofen concentrations are in non-equilibrium with the underlying compartment, i.e. the subcutaneous tissue. Among the dermatopharmacokinetic methods, cutaneous microdialysis is a continuous in vivo sampling technique allowing a full characterization of the unbound concentration-time profiles with a high temporal resolution. These features are especially relevant to investigate with an improved and detailed real-time chronology the rate and the extent to which the drug becomes available at the site of action, i.e. the skin, following topical or systemic delivery.Thèse de doctorat en sciences pharmaceutiques (FARM 3)--UCL, 200

Surface and Bulk Collapse Transitions of Thermoresponsive Polymer Brushes.

We elucidate the sequence of events occurring during the collapse transition of thermoresponsive copolymer brushes based on poly(di(ethyleneglycol) methyl ether methacrylate) chains (PMEO2MA) grown by atom-transfer radical polymerization (ATRP). The collapse of the bulk of the brush is followed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D), and the collapse of its outer surface is assessed by measuring equilibrium water contact angles in the captive bubble configuration. The bulk of the brush collapses over a broad temperature interval (approximately 25 degrees C), and the end of this process is signaled by a sharp first-order transition of the surface of the brush. These observations support theoretical predictions regarding the occurrence of a vertical phase separation during collapse, with surface properties of thermoresponsive brushes exhibiting a sharp variation at a temperature of T(br)(surf). In contrast, the bulk properties of the brush vary smoothly, with a bulk transition T(br)(bulk) occurring on average approximately 8 degrees C below T(br)(surf) and approximately 5 degrees C below the lower critical solution temperature (LCST) of free chains in solution. These observations should also be valid for planar brushes of other neutral, water-soluble thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM). We also propose a way to analyze more quantitatively the temperature dependence of the QCM-D response of thermoresponsive brushes and deliver a simple thermodynamic interpretation of equilibrium contact angles, which can be of use for other complex temperature-responsive solvophilic systems

Bidimensional Response Maps of Adaptive Thermo- and pH-Responsive Polymer Brushes

We depict the collapse transition of adaptive thermo- and pH-responsive copolymer brushes based on poly(di(ethylene glycol) methyl ether methacrylate-co-methacrylic acid) random copolymer chains (P(MEO(2)MA-co-MAA)) by drawing bidimensional (2D) maps of the swelling ratio versus temperature and pH for different brush compositions. The collapse transition is probed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D). While P(MEO(2)MA) brushes exhibit a thermo-collapse transition around 22 degrees C and P(MAA) brushes display a pH-induced collapse transition at pH = 5.5, P(MEO(2)MA-co-MAA) brushes undergo a collapse transition modulated by either temperature or pH from a swollen state at low temperature and high pH to a collapsed state at high temperature and low pH. By varying the composition of the copolymer in MAA units from 4 to 14 mol %, the brushes switch from a pH-modulated thermo-responsive behavior to a temperature-modulated pH-responsive behavior in water. The 2D maps of swelling ratio also illustrate the complex interplay between pH and temperature, and provide a unique view of the response of adaptive brushes

Study of the percutaneous penetration of flurbiprofen by cutaneous and subcutaneous microdialysis after iontophoretic delivery in rat.

The percutaneous penetration of flurbiprofen delivered by iontophoresis was investigated in the hairless rat. Unbound concentrations of flurbiprofen in dermis and subcutaneous tissue were continuously measured by on-line microdialysis. Simultaneously, a conventional blood sampling was performed. Linear microdialysis probes were implanted in dermis and in subcutaneous tissue at a depth of 398.3 +/- 15.3 and 1878 +/- 35.8 microm, respectively. Commercial patches were used to deliver flurbiprofen for 15 min at a current density of 0.4 mA/cm(2). In vivo recoveries of both probes, determined by using naproxen as retrodialysis calibrator, were 26.0 +/- 0.3 and 72.9 +/- 0.7% for dermal and subcutaneous probe, respectively. After iontophoretic delivery, a gradient in mean tissue unbound concentrations was observed, with a C(max) in dermis of 8.7 +/- 0.4 microg/mL as compared with subcutaneous C(max) of 0.5 +/- 0.1 microg/mL. The area under the unbound concentration curve in dermis was 13-fold higher than that in the subcutaneous tissue. Total plasma concentration curves showed a rapid absorption phase with a T(max) of 30 min and C(max) of 1.8 +/- 0.1 microg/mL. In conclusion, iontophoresis delivery was demonstrated to be efficient to deliver a high amount of flurbiprofen in dermis and underlying tissue with a fast input rate whereas maintaining a low plasma exposure

Fluconazole distribution in rat dermis following intravenous and topical application: a microdialysis study.

The objective of this study was to investigate the skin distribution of fluconazole, a water-soluble antifungal agent, following intravenous (i.v.) and topical administration in the awake freely moving rat. Following i.v. bolus injection of fluconazole (10 mg/kg), a dual-site microdialysis sampling was performed in jugular vein and dermis in five rats. In addition, cutaneous absorption was studied by dermal microdialysis sampling following topical application of Diflucan Gel 0.5% to 12 rats. Fluconazole microdialysate concentrations were measured by on-line HPLC. To calibrate in vivo the probes, a fluorinated analog (UK-54737) of fluconazole was used as retrodialysis marker after demonstrating that recoveries were no different. Following i.v. bolus injection, fluconazole rapidly penetrates into the dermis. Cutaneous microdialysis sampling provided dermal concentrations of fluconazole, which were very similar to the unbound plasma concentrations determined by vascular microdialysis. The distribution equilibrium was rapidly achieved with a dermis-to-plasma partition coefficient of 1.02+/-0.04 (n=5). Following topical application of 0.5 g of Diflucan Gel containing 0.5% of fluconazole, active unbound concentrations in dermis were measured by cutaneous microdialysis for 11 h after application. The area under the curve (AUC) of fluconazole in dermal dialysate was relatively constant to an implantation depth of approximately 350 microm. Below this depth, the AUC progressively decreased with increasing implantation depth of the probe. Finally, this study shows that cutaneous microdialysis is an effective and minimally invasive tool to evaluate the dermal pharmacokinetics of fluconazole following intravenous or topical administration