Physicochemical Characterisation of a Novel Thermogelling Formulation for Percutaneous Penetration of 5-Aminolevulinic Acid

Photoprotection and skin irritation effect of hydrogels containing hydroalcoholic extract of red propolis: A natural pathway against skin cancer

The use of natural products in sunscreen formulations as a prophylactic measure against skin cancer is receiving special attention attributed to the photoprotective and antioxidant properties of their chemical components. In this work, we describe the development of topical hydrogel formulations containing hydroalcoholic extract of red propolis (HERP), and the evaluation of the dermal sensitizing effect of the developed products. Sunscreen formulations composed of HERP in different concentrations (1.5, 2.5 or 3.5% w/w) alone or in combination with a chemical (octyl methoxycinnamate) and/or physical (titanium dioxide) filters were developed using poloxamer 407 as gel basis. The preliminary and accelerated stability tests, texture analysis and spreadability tests were performed. All formulations revealed to be stable in preliminary stability assessment. The formulations containing HERP 1.5 and 2.5% alone or associated with the filters showed intense modifications during accelerated stability test, which were confirmed by rheological analyses. The incorporation of HERP and filters in the poloxamer hydrogel decreased the toughness of product (p < 0.05) and the formulation containing HERP alone presented the lowest adhesivity (p < 0.001). The incorporation of HERP in the hydrogel decreased the poloxamer transition temperature, showing different rheological behavior with the increase of HERP concentration. The developed formulations were stable, exhibited non-Newtonian and pseudoplastic behavior, showing in vivo skin compatibility and no skin irritancy.

Antifungal efficacy of liquid poloxamer 407-based emulsions loaded with sertaconazole nitrate

Drug delivery into the human nail plate for the treatment of onychomycosis is difficult due to limited permeability of the nail plate. Semisolid poloxamer 407-based formulations have recently shown promising results for drug delivery into and through the nail plate. In this study, liquid poloxamer 407-based emulsions loaded with sertaconazole nitrate have been developed and the permeation behavior was determined in vitro using modified Franz diffusion cells. The antifungal efficacy was evaluated in an infected nail plate model, where the growth inhibition of Trichophyton rubrum was observed. Bovine hoof plates and keratin films made from human hair were used as models for the human nail plate. In both cases, formulations with low viscosity and high water content showed best results despite a lower solubility of sertaconazole nitrate, suggesting that the composition of the vehicle plays a major role in permeation through the membrane. In addition, an API content close to saturation solubility had a positive effect on permeation.

Photodynamic therapy for skin cancer: How to enhance drug penetration?

Photodynamic therapy (PDT) induced by protoporphyrin IX (PpIX) has been widely used in dermatological practices such as treatment of skin cancers. Clearance rate depends on different factors such as light irradiation, skin oxygenation and drug penetration. The poor penetration of 5-aminolevulinic acid (5-ALA) with topical application is limited and restrains the production of PpIX which could restrict PDT outcomes. This review will focus on techniques already used to enhance drug penetration in human skin, and will present their results, advantages, and drawbacks. Chemical and physical pretreatments will be discussed. Chemical pre-treatments comprise of drug formulation modification, use of agents that modify the heme cycle, enhance PpIX formation, and the combination of differentiation-promoting agent prior to PDT. On the other hand, physical pretreatments affect the skin barrier by creating holes in the skin or by removing stratum corneum. To promote drug penetration, iontophoresis and temperature modulation are interesting alternative methods. Cellular mechanisms enrolled during chemical or physical pretreatments have been investigated in order to understand how 5-ALA penetrates the skin, why it is preferentially metabolized in PpIX in tumour cells, and how it could be accumulated in deeper skin layers. The objective of this review is to compare clinical trials that use innovative technology to conventional PDT treatment. Most of these pretreatments present good or even better clinical outcomes than usual PDT.

5-Aminolevulinic acid coated microneedles for photodynamic therapy of skin tumors

This study evaluated the potential of coated microneedles for improved dermal delivery of 5-aminolevulinic acid (5-ALA), which naturally gets converted by cells of the tissue in to a photosensitizer called protoporphyrin IX (PPIX). Microneedle patches containing 57 microneedles were coated with 5-ALA using an in-house developed micro-precision dip coater. The coating process was optimized to achieve higher 5-ALA loading on microneedles and a high delivery efficiency into porcine cadaver skin. Using 5 dips with 25% w/v 5-ALA solution, a mass of about 350μg of 5-ALA was coated per patch, which gave a delivery efficiency of about 90% in porcine cadaver skin. Bright-field and scanning electron microscopy established that coatings of 5-ALA on microneedles of the patch were uniform. In vivo dermal pharmacokinetics showed that delivery of just 350μg of 5-ALA using coated microneedles led to about 3.2-fold higher PPIX formation after 4h, as compared to topical application of 20% w/w 5-ALA in a conventional cream formulation (25mg cream). Furthermore, with use of coated microneedles, PPIX was observed in deeper regions of the skin (~480μm) as compared to topical 5-ALA cream formulation (~150μm). The potential of PPIX for photodynamic therapy was tested in vivo. After light exposure (633nm; 118J/cm(2)), PPIX got photosensitized, and due to higher initial amount of PPIX in the coated microneedle group, about twice the amount of PPIX was photobleached compared to topical cream application. Finally, even with a lower dose of just 1.75mg 5-ALA, coated microneedles suppressed the growth of subcutaneous tumors by ~57%, while a topical cream containing 5mg of 5-ALA did not suppress the tumor volume and led to tumor growth comparable to the untreated control group. Overall, the strategy of delivering 5-ALA using coated microneedles could be a promising approach for photodynamic therapy of skin tumors.

Dermal quercetin smartCrystals®: Formulation development, antioxidant activity and cellular safety

Flavonoids are natural plant pigments, which possess high antioxidative and antiradical activities. However, their poor water solubility led to a limited bioavailability. To overcome this major hurdle, quercetin nanocrystals were produced implementing smartCrystals® technology. This process combines bead milling and subsequent high-pressure homogenization at relatively low pressure (300bar). To test the possibility to develop a dermal formulation from quercetin smartCrystals®, quercetin nanosuspensions were admixed to Lutrol® F127 and hydroxythylcellulose nonionic gels. The physicochemical properties (morphology, size and charge), saturation solubility, dissolution velocity and the antioxidant properties (DPPH assay) as well as the cellular interaction of the produced quercetin smartCrystals® were studied and compared to crude quercetin powder. Quercetin smartCrystals® showed a strong increase in the saturation solubility and the dissolution velocity (7.6 fold). SmartCrystals® loaded or not into gels proved to be physically stable over a period of three months at 25°C. Interestingly, in vitro DPPH assay confirmed the preservation of quercetin antioxidative properties after nanonization. In parallel, the nanocrystalline form did not display cellular toxicity, even at high concentration (50μg/ml), as assayed on an epithelial cell line (VERO cells). In addition, the nanocrystalline form confirmed a protective activity for VERO cells against hydrogen peroxide induced toxicity in vitro. This new formulation presents a promising approach to deliver quercetin efficiently to skin in well-tolerated formulations.

Preclinical evaluation of thermoreversible triamcinolone acetonide hydrogels for drug delivery to the inner ear

Intratympanic glucocorticoid therapy aims to reduce the side effects associated with systemic long-time therapy of inner ear diseases or traumata after cochlear implantation. For that purpose, thermoreversible hydrogels being fluid at room temperature but solid at body temperature are known to be appropriate drug delivery systems. In this work, the two key parameters sol–gel transition time and temperature of Poloxamer 407 (POX 407) based hydrogels containing oto-compatible micronized triamcinolone acetonide (TAAc) were evaluated by rheological experiments varying the concentrations of the different compounds. A 20% POX 407 hydrogel in PBS containing 30% TAAc emerged as the most appropriate formulation. Oscillation–rotation–oscillation studies at two temperature levels were found to be an useful in-vitro test system for the hydrogel which revealed sufficient storage stability at 4 °C, injectability of the sol, solidification within 20 s at body temperature and persistent stiffness indicating prolonged adhesion at the round window membrane. According to the in-vitro release studies using the Transwell™ system, absorption of the poor water soluble TAAc is partly due to the low amount of dissolved drug but predominantly due to micellar transport resulting in a cumulative release of 262.6 ± 13.4 μg TAAc within one week followed by a sustained release of 193.1 ± 8.3 μg TAAc within the next three weeks. Thus, the formation of POX 407 micelles is the basis not only for gel formation but also absorptivity of TAAc. All in all, fine tuned rheological experiments and absorption studies emerged as useful tools for preclinical evaluation of intratympanally administered hydrogels.

Comprehensive review on additives of topical dosage forms for drug delivery

Skin is the largest organ of the human body and plays the most important role in protecting against pathogen and foreign matter. Three important modes such as topical, regional and transdermal are widely used for delivery of various dosage forms. Among these modes, the topical dosage forms are preferred because it provides local therapeutic activity when applied to the skin or mucous membranes. Additives or pharmaceutical excipients (non-drug component of dosage form) are used as inactive ingredients in dosage form or tools for structuring dosage forms. The main use of topical dosage form additives are controling the extent of absorption, maintaining the viscosity, improving the stability as well as organoleptic property and increasing the bulk of the formulation. The overall goal of this article is to provide the clinician with information related to the topical dosage form additives and their current major applications against various diseases.

Preparation, characterization, and in vitro permeation study of terbinafine HCl in poloxamer 407-based thermogelling formulation for topical application

Upon topical administration, a high penetration rate of antifungal drug into the infected site is desirable to reduce treatment length and systemic side effects which occur especially after a prolonged peroral administration. Thermogelling formulations composed of poloxamer 407, medium chain triglycerides, isopropyl alcohol, dimethyl isosorbide, and water for topical application were developed, and a lipophilic drug terbinafine HCl (TBF) was incorporated. Previously, a remarkable high permeation rate of a hydrophilic drug 5-aminolevulinic acid from this vehicle was evident compared to different creams from German Pharmacopoeia. By varying the composition of vehicle constituents, a broad range of consistencies and appearances was obtained. Up to 4% TBF could be solubilized in the vehicle. TBF fluxes at steady state across human stratum corneum from these formulations were higher than those from the German Pharmacopoeia Basiscreme Deutscher Arzneimittel Codex and a marketed product at similar concentration of 1%. TBF fluxes increased along with a higher content of TBF in the formulation. The amount of TBF retained in stratum corneum was higher compared to those from both standards of comparison (p < 0.01). The thermodynamic activity of TBF in the thermogelling formulation was lower compared to those in other formulations. Therefore, the nature of the vehicle and its interaction with TBF are suggested to play a significant role in explaining higher fluxes along with higher TBF content. Differential scanning calorimetry measurements revealed comparable T2 and T3 endothermic shifts from all examined formulations suggesting equal influences to the skin lipids.

A novel transdermal delivery system for the anti-inflammatory lumiracoxib: influence of oleic acid on in vitro percutaneous absorption and in vivo potential cutaneous irritation

Transdermal delivery of non-steroidal anti-inflammatory drugs may be an interesting strategy for delivering these drugs to the diseased site, but it would be ineffective due to low skin permeability. We investigated whether oleic acid (OA), a lipid penetration enhancer in poloxamer gels named poloxamer-based delivery systems (PBDS), can improve lumiracoxib (LM) delivery to/through the skin. The LM partition coefficient (K) studies were carried out in order to evaluate the drug lipophilicity grade (K(octanol/buffer)), showing values >1 which demonstrated its high lipophilicity. Both in vitro percutaneous absorption and skin retention studies of LM were measured in the presence or absence of OA (in different concentrations) in PBDS using porcine ear skin. The flux of in vitro percutaneous absorption and in vitro retention of LM in viable epidermis increased in the presence of 10.0% (w/w) OA in 25.0% (w/w) poloxamer gel. In vivo cutaneous irritation potential was carried out in rabbits showing that this formulation did not provide primary or cumulative cutaneous irritability in animal model. The results showed that 25.0% poloxamer gel containing 10.0% OA is potential transdermal delivery system for LM.

Development of microemulsions to topically deliver 5-aminolevulinic acid in photodynamic therapy

The aim of this study was to obtain and to characterize microemulsions containing 5-aminolevulinic acid (5-ALA) and to investigate the influence of these systems in drug skin permeation for further topical photodynamic therapy (PDT). 5-ALA was incorporated in water-in-oil (W/O), bicontinuous (Bc), and oil-in-water (O/W) microemulsions obtained by the titration of ethyl oleate and PEG-8 caprylic/capric glycerides:polyglyceryl-6 dioleate (3:1) mixtures with water. Selected systems were characterized by conductivity, viscosity, size of the droplets, and drug release. The stability of the drug in the microemulsions was also assessed. Moreover, the in vitro and in vivo skin permeation of 5-ALA was investigated using diffusion cells and confocal scanning laser microscopy (CSLM), respectively. Despite the fact that the O/W microemulsion decreased the 5-ALA diffusion coefficient and retarded the drug release, it also significantly increased the in vitro drug skin permeation when compared to other 5-ALA carriers. It was observed by CSLM that the red fluorescence of the skin increased homogeneously in the deeper skin layers when the 5-ALA microemulsion was applied in vivo, probably due to the formation of the photoactive protoporphyrin IX. The microemulsion developed carried 5-ALA to the deeper skin layers, increasing the red fluorescence of the skin and indicating the potentiality of the system for topical 5-ALA-PDT.