Franz Feichtner

Dermal PK/PD of a lipophilic topical drug in psoriatic patients by continuous intradermal membrane-free sampling.

BACKGROUND Methodologies for continuous sampling of lipophilic drugs and high-molecular solutes in the dermis are currently lacking. We investigated the feasibility of sampling a lipophilic topical drug and the locally released biomarker in the dermis of non-lesional and lesional skin of psoriatic patients over 25h by means of membrane-free dermal open-flow microperfusion probes (dOFM) and novel wearable multi-channel pumps. METHODS Nine psoriatic patients received a topical p-38 inhibitor (BCT194, 0.5% cream) on a lesional and a non-lesional application site once daily for 8 days. Multiple dOFM sampling was performed for 25 h from each site on day 1 and day 8. Patients were mobile as dOFM probes were operated by a novel light-weight push-pull pump. Ultrasound was used to verify intradermal probe placement, cap-LC-MS/MS for BCT194 and ELISA for TNFα analysis. RESULTS dOFM was well tolerated and demonstrated significant drug concentrations in lesional as well as non-lesional skin after 8 days, but did not show significant differences between tissues. On day 8, TNFα release following probe insertion was significantly reduced compared to day 1. CONCLUSIONS Novel membrane-free probes and wearable multi-channel pumps allowed prolonged intradermal PK/PD profiling of a lipophilic topical drug in psoriatic patients. This initial study shows that dOFM overcomes limitations of microdialysis sampling methodology, and it demonstrates the potential for PK/PD studies of topical products and formulations in a clinical setting.

Microdialysis--a versatile technology to perform metabolic monitoring in diabetes and critically ill patients.

Continuous subcutaneous glucose monitoring has been tested in type 1 diabetes (T1D). Since in critically ill patients vascular access is granted vascular microdialysis may be preferential. To test this hypothesis comparative accuracy data for microdialysis applied for peripheral venous and subcutaneous glucose monitoring was obtained in experiments in T1D patients. Twelve T1D patients were investigated for up to 30 h. Extracorporeal vascular (MDv) and subcutaneous microdialysis (MDs) was performed. Microdialysis samples were collected in 15-60 min intervals, analyzed for glucose and calibrated to reference. MDv and MDs glucose levels were compared against reference. Median absolute relative difference was 14.0 (5.0; 28.0)% (MDv) and 9.2 (4.4; 18.4)% (MDs). Clarke Error Grid analysis showed that 100% (MDv) and 98.8% (MDv) were within zones A and B. Extracorporeal vascular and standard subcutaneous microdialysis indicated similar performance in T1D. We suggest microdialysis as a versatile technology for metabolite monitoring in subcutaneous tissue and whole blood.

Clinical applicability of dOFM devices for dermal sampling

Sampling the dermal interstitial fluid (ISF) allows the pharmacokinetics and pharmacodynamics of dermatological drugs to be studied directly at their site of action.

A Stepwise Approach toward Closed-Loop Blood Glucose Control for Intensive Care Unit Patients: Results from a Feasibility Study in Type 1 Diabetic Subjects Using Vascular Microdialysis with Infrared Spectrometry and a Model Predictive Control Algorithm

Background: Glycemic control can reduce the mortality and morbidity of intensive care patients. The CLINICIP (closed-loop insulin infusion for critically ill patients) project aimed to develop a closed-loop control system for this patient group. Following a stepwise approach, we combined three independently tested subparts to form a semiautomatic closed-loop system and evaluated it with respect to safety and performance aspects by testing it in subjects with type 1 diabetes mellitus (T1DM) in a first feasibility trial. Methods: Vascular microdialysis, a multianalyte infrared spectroscopic glucose sensor, and a standard insulin infusion pump controlled by an adaptive model predictive control (MPC) algorithm were combined to form a closed-loop device, which was evaluated in four T1DM subjects during 30-hour feasibility studies. The aim was to maintain blood glucose concentration in the target range between 80 and 110 mg/dl. Results: Mean plasma glucose concentration was 110.5 ± 29.7 mg/dl. The MPC managed to establish normoglycemia within 105 ± 78 minutes after trial start and managed to maintain glucose concentration within the target range for 47% of the time. The hyperglycemic index averaged to 11.9 ± 5.3 mg/dl. Conclusion: Data of the feasibility trial illustrate the device being effective in controlling glycemia in T1DM subjects. However, the monitoring part of the loop must be improved with respect to accuracy and precision before testing the system in the target population.

Lipid‐Heparin Infusion Suppresses the IL‐10 Response to Trauma in Subcutaneous Adipose Tissue in Humans

An imbalance between pro‐ and anti‐inflammatory cytokine productions in adipose tissue is thought to contribute to chronic, systemic, low‐grade inflammation and consequently to an increased risk of cardiovascular complications in obese and type 2 diabetic patients. Nonesterified fatty acids (NEFA), whose serum levels are elevated in such patients, have been shown to interfere with cytokine production in vitro. In order to evaluate the effects of elevated NEFA levels on cytokine production in adipose tissue in vivo we used an 18‐gauge open‐flow microperfusion (OFM) catheter to induce local inflammation in the subcutaneous adipose tissue (SAT) of healthy volunteers and to sample interstitial fluid (IF) specifically from the inflamed tissue. In two crossover studies, nine subjects received either an intravenous lipid‐heparin infusion to elevate circulating NEFA levels or saline over a period of 28 h. The former increased the circulating levels of triglycerides (TGs), NEFA, glucose, and insulin over the study period. NEFA effects on locally induced inflammation were estimated by measuring the levels of a panel adipokines in the OFM probe effluent. Interleukin‐6 (IL‐6), IL‐8, tumor necrosis factor‐α (TNF‐α) and monocyte chemoattractant protein‐1 (MCP‐1) levels increased during the study period but were not affected by lipid‐heparin infusion. In contrast, the level of IL‐10, an anti‐inflammatory cytokine, was significantly reduced during the final hour of lipid‐heparin infusion (saline: 449.2 ± 105.9 vs. lipid‐heparin: 65.4 ± 15.4 pg/ml; P = 0.02). These data provide the first in vivo evidence that elevated NEFA can modulate cytokine production by adipose tissue.

Microdialysis based monitoring of subcutaneous interstitial and venous blood glucose in Type 1 diabetic subjects by mid-infrared spectrometry for intensive insulin therapy

Implementing strict glycemic control can reduce the risk of serious complications in both diabetic and critically ill patients. For this purpose, many different blood glucose monitoring techniques and insulin infusion strategies have been tested towards the realization of an artificial pancreas under closed loop control. In contrast to competing subcutaneously implanted electrochemical biosensors, microdialysis based systems for sampling body fluids from either the interstitial adipose tissue compartment or from venous blood have been developed, which allow an ex-vivo glucose monitoring by mid-infrared spectrometry. For the first option, a commercially available, subcutaneously inserted CMA 60 microdialysis catheter has been used routinely. The vascular body interface includes a double-lumen venous catheter in combination with whole blood dilution using a heparin solution. The diluted whole blood is transported to a flow-through dialysis cell, where the harvesting of analytes across the microdialysis membrane takes place at high recovery rates. The dialysate is continuously transported to the IR-sensor. Ex-vivo measurements were conducted on type-1 diabetic subjects lasting up to 28 hours. Experiments have shown excellent agreement between the sensor readout and the reference blood glucose concentration values. The simultaneous assessment of dialysis recovery rates renders a reliable quantification of whole blood concentrations of glucose and metabolites (urea, lactate etc) after taking blood dilution into account. Our results from transmission spectrometry indicate, that the developed bed-side device enables reliable long-term glucose monitoring with reagent- and calibration-free operation.

An Automated Discontinuous Venous Blood Sampling System for Ex Vivo Glucose Determination in Humans

Background: Intensive insulin therapy reduces mortality and morbidity in critically ill patients but places great demands on medical staff who must take frequent blood samples for the determination of glucose levels. A cost-effective solution to this resourcing problem could be provided by an effective and reliable automated blood sampling (ABS) system suitable for ex vivo glucose determination. Method: The primary study aim was to compare the performance of a prototype ABS system with a manual reference system over a 30 h sampling period under controlled conditions in humans. Two venous cannulae were inserted to connect the ABS system and the reference system. Blood samples were taken with both systems at 15, 30, and 60 min intervals and analyzed using a Beckman glucose analyzer. During the study, blood glucose levels were altered through four meal ingestions. Results: The median Pearson coefficient of correlation between manually and automatically withdrawn blood samples was 0.976 (0.953–0.996). The system error was −3.327 ± 5.546% (−6.03–0.49). Through Clark error grid analysis, 420 data pairs were analyzed, showing that 98.6% of the data were in zone A and 1.4% were in zone B. Insulin titration error grid analysis revealed an acceptable treatment in 100% of cases. A 17.5-fold reduction in the occurrence of blood-withdrawal failures through occluded catheters was moreover achieved by the added implementation in the ABS system of a “keep vein open” saline infusion. Conclusions: Our study showed that the ABS system described provides a user-friendly, reliable automated means for reproducible and accurate blood sampling from a peripheral vein for blood glucose determination and thus represents a promising alternative to frequent manual blood sampling.

Certified dOFM sampling devices provide access to target tissue in pharmaceutical trials

Clinical testing of dermatological drugs requires access to the site of drug action within the dermis. Conventional methods such as skin biopsies are rather invasive and provide limited data on the kinetics and dynamics of drugs. We present minimally invasive dermal sampling probes and a wearable pump for continuous sampling from the dermis. These dermal open flow microperfusion (dOFM) devices comply with international medical device guidelines (CE certified) and have demonstrated applicability and tolerability in clinical trials. dOFM is likely to become an invaluable tool for clinical bioequivalence trials prior to market release of generic drugs.

Novel catheters for in vivo research and pharmaceutical trials providing direct access to extracellular space of target tissues

Medical and pharmaceutical research frequently requires direct access to the site of action of drugs and the withdrawal of tissue samples rather than withdrawal of blood samples. As alternative to invasive biopsy procedures less invasive continuous sampling techniques such as Microdialysis (μD) and Open-Flow Microperfusion (OFM) have been developed since the 1970ties. While μD-catheters recover substances through semi-permeable membranes OFM-catheters are membrane-free and thus permeable for all substances of interest at tissue level. We aimed at utilizing the advantages of the OFM principle and to develop catheters suitable for intradermal insertion to facilitate research in dermatology. Moreover, we aimed at demonstrating the feasibility of sampling lipophilic drugs from the dermis of patients in a clinical trial.