Purpose Topical nonsteroidal anti‐inflammatory drug formulations are used commonly to treat musculoskeletal pain and inflammation. Drug properties and formulation composition are the primary determinants of the transdermal drug delivery rate. The ex vivo transdermal flux through human skin of three topical diclofenac formulations was compared. Methods The formulations tested were hydrogel 1% diclofenac sodium and two emulsion gels (1.16%/2.32% diclofenac diethylamine, equivalent to 1%/2% diclofenac sodium). Human abdominal skin obtained during unrelated surgical procedures was stored at −20 °C until use. Skin specimens were thawed, prepared and placed in Franz diffusion cells (stratum corneum facing donor cell). The test formulation (~200 mg) was applied to the donor cell skin surface, and the receptor compartment was periodically sampled over 48 hours. The drug concentration in the receptor medium was determined by a validated HPLC method. Raman spectral imaging was performed to visualize the location and distribution of diclofenac. Results After 5 hours, the cumulative amount of hydrogel diclofenac transiting the skin was about 10 times that of the emulsion gel 1.16% (P=0.0004) and about twice that of the emulsion gel 2.32% (P=0.022). Similar results were seen after 9 hours. Raman spectroscopy showed that the hydrogel formulation was a homogeneous mixture of its various components, including diclofenac. The emulsion gels were non‐homogeneous, with diclofenac in close proximity to the lipophilic (paraffin) phase. Conclusions The transdermal transit of diclofenac from the hydrogel demonstrated a faster onset and a greater absorption rate than either emulsion gel formulation, suggesting that the hydrogel formulation may have a faster onset of action in underlying tissues vs. the emulsion gel products.

No abstract

ZusammenfassungFür in pflanzlichen Drogen enthaltene Mucopolysaccharide wird eine Bioadhäsion an Schleimhäuten und damit ein Schutz vor irritativen Noxen beschrieben. Um hier weitere Kenntnisse zu erhalten, wurden verschiedene pflanzliche Drogen und auch Fertigprodukte in zwei verschiedenen experimentellen In-vitro-Studien unter Verwendung von buccaler Schleimhaut des Schweins untersucht. Gezeigt werden konnte zunächst ein verlangsamter Abfluss zweier unterschiedlicher Althaea-radix-enthaltender Zubereitungen auf der Schleimhaut, fixiert auf einer schiefen Ebene, was auf bioadhäsive Eigenschaften hinweist. In einem weiteren Modell mit der Franz-Diffusionszelle wurde der Einfluss auf die Permeation von Coffein durch die buccale Schleimhaut des Schweins untersucht. Hier wurde eine deutliche Hemmung der Permeation durch die Fertigprodukte (Hustensäfte bzw. Sirupe), jedoch kein oder kein eindeutiger Effekt für einen Althaea-officinalis-Extrakt als alleinigen Wirkstoff gefunden. Für die schleimhautprotektiven Wirkungen Mucopolysaccharid-haltiger Drogen dürfte zumindest gemäß den Ergebnissen in diesen Modellen auch die galenische Zusammensetzung eine bedeutsame Rolle spielen.

In view of increasing numbers of dermatological disorders, transdermal drug delivery along with in vitro research is becoming increasingly popular. Herefore, qualified in vitro skin models are required. The objective of this study was the optimization and validation of a modified lactate dehydrogenase (LDH) release assay during the establishment of an in vitro viable human skin model, employable for a variety of skin associated disorders. Firstly, the most suitable LDH isoform for the study was determined. Subsequently, a stability study was conducted to investigate the best storage conditions of the LDH enzyme. Finally, the test system was validated in terms of linear range, range limits and system suitability. The results indicate LDH-5 as most suitable isoform due to its predominance in skin. The stability samples stored at −20 °C in the presence of polyethylene glycol (PEG) as cryoprotector displayed the targeted recovery of 100% ± 15 % until the end of the four-week study in contrast to other investigated conditions. A six-point calibration without PEG and a seven-point calibration with PEG including evaluation of system suitability and quantification limits were established with both correlation coefficients r 2 above 0.99 and all deviations below 15%. Concluding from those results, this method can be considered valid and useful for its employment in viability determination of viable in vitro skin models.

Transdermal drug delivery provides several advantages over conventional drug administration, such as the avoidance of first-pass metabolism and better patient compliance. In vitro research can abbreviate and facilitate the pharmaceutical development considerably compared to in vivo research as drug screening and clinical studies can be reduced. These advantages led to the development of corresponding skin models. Viable skin models are more useful than non-viable ones, due to the influence of skin metabolism on the results. While most in vitro studies concentrate on evaluating human-based models, the current study is designed for the investigation of both human and animal diseases. So far, there is little information available in the literature about viable animal skin cultures which are in fact intended for application in the veterinary and not the human field. Hence, the current study aims to fill the gap. For the in vitro viable skin model, specimens of human, porcine and canine skin were cultured over two weeks under serum-free conditions. To evaluate the influence of medium supplementation on skin viability, two different supplement mixtures were compared with basic medium. The skin specimens were maintained at a viability-level >50% until the end of the study. From the tested supplements, the addition of bovine pituitary extract and epidermal growth factor increased skin viability whereas hydrocortisone and insulin induced a decrease. This in vitro viable skin model may be a useful tool for the investigation of skin diseases, especially for the veterinary field.