Novel nanocrystal-based formulations of apremilast for improved topical delivery

Dexamethasone nanocrystals-embedded hydroxypropyl methylcellulose hydrogel increases cochlear delivery and attenuates hearing loss following intratympanic injection

Herein, dexamethasone (DEX) nanocrystalline suspension (NS)-embedded hydrogel (NS-G) was constructed using a hydroxypropyl methylcellulose (HPMC) polymer to enhance cochlear delivery and attenuate hearing loss following intratympanic (IT) injection. Hydrophobic steroidal nanocrystals were prepared using a bead milling technique and incorporated into a polysaccharide hydrogel. The NS-G system with HPMC (average molecular weight, 86,000 g/mol; 15 mg/mL) was characterized as follows: rod-shaped drug crystalline; particle size <300 nm; and constant complex viscosity ≤1.17 Pa·s. Pulverization of the drug particles into submicron diameters enhanced drug dissolution, while the HPMC matrix increased the residence time in the middle ear cavity, exhibiting a controlled release profile. The IT NS-G system elicited markedly enhanced and prolonged drug delivery (> 9 h) to the cochlear tissue compared with that of DEX sodium phosphate (DEX-SP), a water-soluble prodrug. In mice with kanamycin- and furosemide-induced ototoxicity, NS-G markedly enhanced hearing preservation across all frequencies (8-32 kHz), as revealed by an auditory brainstem response test, compared with both saline and DEX-SP. Moreover, treatment with NS-G showed enhanced anti-inflammatory effects, as evidenced by decreased levels of inflammation-related cytokines. Therefore, the IT administration of DEX NS-loaded HPMC hydrogels is a promising strategy for treating hearing loss.

Nanocrystal formulations of mebendazole employing Quality by Design and molecular level insights by atomistic simulations

OBJECTIVE

The present study investigates the production of mebendazole nanocrystal formulations by wet media milling.

SIGNIFICANCE

Nanocrystal formulations are expected to enhance the dissolution properties of mebendazole, which possesses poor solubility, highly dependent on crystal polymorphism.

METHODS

A Box-Behnken design was employed to study the effects of formulation and process variables on the nanocrystal size and ζ-potential. The optimal nanosuspensions were solidified by spay-drying and freeze-drying with and without mannitol, and the effects of the drying method on the reconstitution of the nanosuspension was studied. Additionally, their physicochemical properties were determined, while the mechanism of fracture and stabilizer adsorption were investigated by atomistic simulations.

RESULTS

Poloxamer 407 is the most suitable stabilizer, while the bead size, milling speed, and stabilizer content significantly affect the diameter. The ζ-potential is affected by the stabilizer concentration depending on bead size. Energy-vector diagrams revealed a slip plane in the lattice of form C, while molecular dynamics simulations revealed strong interactions between stabilizer and crystal surface. Both drying processes induce polymorphic transformation to form A, which, however, can be partially prevented by the addition of mannitol in freeze-drying, at the expense of suspension redispersibility. The spray-dried nanosuspensions exhibited substantially enhanced dissolution profile compared to neat mebendazole, probably due to reduction of particle size, despite transformation to the unfavorable form A.

CONCLUSIONS

Nanocrystal formulations exhibited significant dissolution enhancement, while experimental design and atomistic simulations provided useful insights into the mechanism of their formation and stability.

Recent Advancements and Trends of Topical Drug Delivery Systems in Psoriasis: A Review and Bibliometric Analysis

Psoriasis is an immune-mediated inflammatory skin disease where topical therapy is crucial. While various dosage forms have enhanced the efficacy of current treatments, their limited permeability and lack of targeted delivery to the dermis and epidermis remain challenges. We reviewed the evolution of topical therapies for psoriasis and conducted a bibliometric analysis from 1993 to 2023 using a predictive linear regression model. This included a comprehensive statistical and visual evaluation of each model's validity, literature profiles, citation patterns, and collaborations, assessing R variance and mean squared error (MSE). Furthermore, we detailed the structural features and penetration pathways of emerging drug delivery systems for topical treatment, such as lipid-based, polymer-based, metallic nanocarriers, and nanocrystals, highlighting their advantages. This systematic overview indicates that future research should focus on developing novel drug delivery systems characterized by enhanced stability, biocompatibility, and drug-carrying capacity.

Calcipotriol Nanosuspension-Loaded Trilayer Dissolving Microneedle Patches for the Treatment of Psoriasis: In Vitro Delivery and In Vivo Antipsoriatic Activity Studies

Psoriasis, affecting 2-3% of the global population, is a chronic inflammatory skin condition without a definitive cure. Current treatments focus on managing symptoms. Recognizing the need for innovative drug delivery methods to enhance patient adherence, this study explores a new approach using calcipotriol monohydrate (CPM), a primary topical treatment for psoriasis. Despite its effectiveness, CPM's therapeutic potential is often limited by factors like the greasiness of topical applications, poor skin permeability, low skin retention, and lack of controlled delivery. To overcome these challenges, the study introduces CPM in the form of nanosuspensions (NSs), characterized by an average particle size of 211 ± 2 nm. These CPM NSs are then incorporated into a trilayer dissolving microneedle patch (MAP) made from poly(vinylpyrrolidone) and w poly(vinyl alcohol) as needle arrays and prefrom 3D printed polylactic acid backing layer. This MAP features rapidly dissolving tips and exhibits good mechanical properties and insertion capability with delivery efficiency compared to the conventional Daivonex ointment. The effectiveness of this novel MAP was tested on Sprague-Dawley rats with imiquimod-induced psoriasis, demonstrating efficacy comparable to the marketed ointment. This innovative trilayer dissolving MAP represents a promising new local delivery system for calcipotriol, potentially revolutionizing psoriasis treatment by enhancing drug delivery and patient compliance.

Development of posaconazole nanocrystalline solid dispersion: preparation, characterization and in vivo evaluation

OBJECTIVE

Posaconazole (PCZ) is an antifungal drug, which acts by inhibiting the lanosterol-14α-demethylase enzyme. It is a biopharmaceutical classification system class II drug with its bioavailability being limited by poor aqueous solubility. The aim of this study was to improve the oral bioavailability of PCZ by preparing nanocrystalline solid dispersion (NCS).

METHODS

PCZ-NCS was prepared by a combination of precipitation and high-pressure homogenization followed by freeze-drying. Several different surfactants and polymers were screened to produce NCS with smaller particle size and higher stability.

RESULTS

The optimized NCS formulation containing 0.2% Eudragit S100 and 0.2% SLS was found to provide the average particle size of 73.31 ± 4.7 nm with a polydispersity index of 0.23 ± 0.03. Scanning electron microscopy revealed the preparation of homogeneous and rounded particles. Differential scanning calorimetry and X-ray diffraction confirmed crystalline nature of NCS. Nanonization increased the saturation solubility of PCZ by about 18-fold in comparison with the neat drug. Intrinsic dissolution study showed 93% dissolution of PCZ within the first 10 min. In vivo pharmacokinetic study in Wistar rats showed that Cmax and AUCtotal of PCZ-NCS increased by 2.58- and 2.64-fold compared to the marketed formulation.

CONCLUSION

PCZ-NCS formulation presents a viable approach for enhancing the oral bioavailability of PCZ.

Formulation characterization of lecithin organogel as topical drug delivery system for psoriasis: In-vitro permeation and preclinical evaluation

Psoriasis is a chronic inflammatory and proliferative skin disease that causes pathological skin changes and has a substantial impact on the quality of patient life. Apremilast was approved by the US Food and Drug Administration as an oral medication for psoriasis and is beneficial in mild to moderate conditions for chronic usage. However, 5%-7% of withdrawals were reported due to severe side effects. To address the issue, a localized drug delivery strategy via the topical route may be a viable approach. However, poor physicochemical properties make it vulnerable to passing through the skin, requiring a specialized drug delivery system to demonstrate its full potential via a topical route like lecithin organogel. The formulation was optimized by screening the suitable lecithin type and non-polar solvents based on the gel formation ability of lecithin and the solubility of apremilast in the solvent. The pseudo-ternary diagram was used to optimize the water content required to form the gel. The optimized gel was found to be shear thinning characterized for rheological parameters, in-vitro diffusion studies, and in-vitro skin distribution studies. Preclinical studies in Imiquimod-induced mice showed a better reduction in severity index, cytokine levels, and epidermal hyperplasia from the lecithin organogel group compared to the apremilast oral administration and marketed standard topical gel group. Based on these results, lecithin organogel can be considered a promising approach to deliver molecules like apremilast by topical route in psoriatic-like conditions.

Harnessing the potential of fatty Acid-Surfactant-Based micellar gel for enhanced topical delivery of Apremilast in psoriasis treatment

Apremilast (APR) is a potent anti-psoriatic agent that inhibits the phosphodiesterase 4 enzyme. Due to the poor oral bioavailability and associated systemic side effects the clinical applicability of APR has been constrained. Nanotechnology-based carrier system presents a novel option to increase the efficacy of the topical treatment of APR. The current investigation deals with the development of fatty acid-surfactant conjugate-based hybrid mixed micellar gel (HMMG) for the topical delivery of APR. The developed micelles exhibited an average size of 83.59 ± 4.46 nm, PDI of 0.239 ± 0.047, % entrapment efficiency of ∼ 94.78 ± 3.98 %, with % practical drug loading of ∼11.37 ± 3.14 %. TEM analysis revealed the spherical shape of micelles. The hybrid micelles were further loaded in a carbopol®934P gel base for ease of application. Ex vivo permeation study revealed enhanced permeation and ∼ 38-fold higher retention in deeper layers of skin from a hybrid micellar gel. In vivo, assessment demonstrated augmented efficacy of APR-HMMG as compared to 0.1 % betamethasone valerate. Also, APR-HMMG showed no sign of irritation, suggesting superior safety as a topical application. Thus, the proposed formulation strategy represents a viable avenue for enhancing the therapeutic efficacy of various anti-psoriatic moieties.

Nanocrystals and nanosuspensions: an exploration from classic formulations to advanced drug delivery systems

Nanocrystals and nanosuspensions have become realistic approaches to overcome the formulation challenges of poorly water-soluble drugs. They also represent a less-known but versatile platform for multiple therapeutic applications. They can be integrated into a broad spectrum of drug delivery systems including tablets, hydrogels, microneedles, microparticles, or even functionalized liposomes. The recent progresses, challenges, and opportunities in this field are gathered originally together with an informative case study concerning an itraconazole nanosuspension-in-hydrogel formulation. The translational aspects, historical and current clinical perspectives are also critically reviewed here to shed light on the incoming generation of nanocrystal formulations.

Nanocrystal technologies in biomedical science: From the bench to the clinic

The pharmaceutical industry is grappling with a pressing crisis in drug development characterized by soaring R&D costs, setbacks in blockbuster drug development due to poor aqueous solubility, and patent-related limitations on newly approved molecules. To combat these challenges, diverse strategies have emerged to enhance the solubility and dissolution rates of Biopharmaceutics Classification System (BCS) II and IV drug molecules. Enter drug nanocrystals, a revolutionary nanotechnology-driven, carrier-free colloidal drug delivery system. This review provides a comprehensive insight into nanocrystal strategies, stabilizer selection criteria, preparation methods, advanced characterization techniques, the evolving nanocrystal technological landscape, current market options, and exciting clinical prospects for reshaping the future of pharmaceuticals.

New Insights into Pharmaceutical Nanocrystals for the Improved Topical Delivery of Therapeutics in Various Skin Disorders

Nanotechnology has provided nanostructure-based delivery of drugs, among which nanocrystals have been investigated and explored for feasible topical drug delivery. Nanocrystals are nano-sized colloidal carriers, considered pure solid particles with a maximum drug load and a very small amount of stabilizer. The size or mean diameter of the nanocrystals is less than 1 μm and has a crystalline character. Prominent synthesis methods include the utilization of microfluidic- driven platforms as well as the milling approach, which is both adaptable and adjustable. Nanocrystals have shown a high capacity for loading drugs, utilization of negligible amounts of excipients, greater chemical stability, lower toxic effects, and ease of scale-up, as well as manufacturing. They have gained interest as drug delivery platforms, and the significantly large surface area of the skin makes it a potential approach for topical therapeutic formulations for different skin disorders including fungal and bacterial infections, psoriasis, wound healing, and skin cancers, etc. This article explores the preparation techniques, applications, and recent patents of nanocrystals for treating various skin conditions.

Formulation and optimization of ivermectin nanocrystals for enhanced topical delivery

The increasing resistance to antiparasitic drugs and limited availability of new agents highlight the need to improve the efficacy of existing treatments. Ivermectin (IVM) is commonly used for parasite treatment in humans and animals, however its efficacy is not optimal and the emergence of IVM-resistant parasites presents a challenge. In this context, the physico-chemical characteristics of IVM were modified by nanocrystallization to improve its equilibrium water-solubility and skin penetration, potentially improving its therapeutic effectiveness when applied topically. IVM-nanocrystals (IVM-NC) were prepared using microfluidization technique. The impact of several process/formulation variables on IVM-NC characteristics were studied using D-optimal statistical design. The optimized formulation was further lyophilized and evaluated using several in vitro and ex vivo tests. The optimal IVM-NC produced monodisperse particles with average diameter of 186 nm and polydispersity index of 0.4. In vitro results showed an impressive 730-fold increase in the equilibrium solubility and substantial 24-fold increase in dissolution rate. Ex vivo permeation study using pig's ear skin demonstrated 3-fold increase in dermal deposition of IVM-NC. Additionally, lyophilized IVM-NC was integrated into topical cream, and the resulting drug release profile was superior compared to that of the marketed product. Overall, IVM-NC presents a promising approach to improving the effectiveness of topically applied IVM in treating local parasitic infections.

Efficacy of Apremilast Gels in Mouse Model of Imiquimod-Induced Psoriasis Skin Inflammation

Apremilast (APM) is a novel drug for the treatment of psoriasis and psoriatic arthritis. APM is a phosphodiesterase 4 (PDE4) inhibitor, raising intracellular cAMP levels and thereby decreasing the inflammatory response by modulating the expression of TNF-α, IL-17, IL-23, and other inflammatory cytokines. The goal of this study is to develop APM gels as a new pharmaceutical formulation for the treatment of topical psoriasis. APM was solubilized in Transcutol-P and incorporated into Pluronic F127, Sepigel, and carbomer bases at different proportions. All formulations were characterized physiochemically. A biopharmaceutical study (release profile) was performed, and ex vivo permeation was evaluated using a human skin model. A toxicity assay was carried out on the HaCaT cell line. A mouse model of imiquimod-induced psoriasis skin inflammation was carried out to determine its efficacy by histological analysis, RNA extraction, and RT-qPCR assays. APM gel formulations showed good physicochemical characteristics and a sustained release profile. There was no permeation of any gel measured through human skin, indicating a high retained amount of APM on the skin. Cell viability was greater than 80% at most dilution concentrations. APM gels treated the psoriasis mouse model, and it shows a reduction in the proinflammatory cytokines (IL-8, IL-17A, IL-17F, and IL-23). APM gels could be a new approach for the treatment of topical psoriasis.

Factors affecting the preparation of nanocrystals: characterization, surface modifications and toxicity aspects

INTRODUCTION

The fabrication of well-defined nanocrystals in size and form is the focus of much investigation. In this work, we have critically reviewed several recent instances from the literature that shows how the production procedure affects the physicochemical properties of the nanocrystals.

AREAS COVERED

Scopus, MedLine, PubMed, Web of Science, and Google Scholar were searched for peer-review articles published in the past few years using different key words. Authors chose relevant publications from their files for this review. This review focuses on the range of techniques available for producing nanocrystals. We draw attention to several recent instances demonstrating the impact of various process and formulation variables that affect the nanocrystals' physicochemical properties. Moreover, various developments in the characterization techniques explored for nanocrystals concerning their size, morphology, etc. have been discussed. Last but not least, recent applications, the effect of surface modifications, and the toxicological traits of nanocrystals have also been reviewed.

EXPERT OPINION

The selection of an appropriate production method for the formation of nanocrystals, together with a deep understanding of the relationship between the drug's physicochemical properties, unique features of the various formulation alternatives, and anticipated in-vivo performance, would significantly reduce the risk of failure during human clinical trials that are inadequate.

Nanocrystals in cosmetics and cosmeceuticals by topical delivery

The main issues with local delivery of cosmetics are their high sensitivity and limited drug loading of active pharmaceutical ingredient. Nanocrystal technology offers consumers cutting-edge and effective products and exhibits enormous development potential in the beauty business as a new delivery method to address the issue of low solubility and low permeability of sensitive chemicals. In this review, we described the processes for making NCs, along with the impacts of loading and the uses of different carriers. Among them, nanocrystalline loaded gel and emulsion are widely used and may further improve the stability of the system. Then, we introduced the beauty efficacy of drug NCs from five aspects: anti-inflammation and acne, anti-bacterial, lightening and freckle removal, anti-aging as well as UV protection. Following that, we presented the current scenario about stability and safety. Finally, the challenges and vacancy were discussed along with the potential uses of NCs in the cosmetics industry. This review serves as a resource for the advancement of nanocrystal technology in the cosmetics sector.

Nanocrystals as an emerging nanocarrier for the management of dermatological diseases

Skin conditions are amongst the most prevalent health issues in the world and come with a heavy economic, social, and psychological burden. Incurable and chronic skin conditions like eczema, psoriasis, fungal infections are linked to major morbidity in the manner of physical pain and a reduction in quality life of patients. Several drugs have difficulties for penetrating the skin due to the barrier mechanism of the skin layers and the incompatible physicochemical characteristics of the drugs. This has led to the introduction of innovative drug delivery methods. Currently, formulations depend on nanocrystals have indeed been researched for topical administration of drugs and have resulted in enhanced skin penetration. This review focuses on skin penetration barriers, modern methods to enhance topical distribution, and the use of nanocrystals to overcome these barriers. By means of mechanisms such as adherence to skin, creation of diffusional corona, targeting of hair follicles, and the generation of a greater concentration gradient throughout the skin, nanocrystals could enhance transport across the skin. Scientists working on product formulations incorporating chemicals that are "challenging-to-deliver" topically may find the most current findings to be of relevance.

Science of, and insights into, thermodynamic principles for dermal formulations

Studies have demonstrated the significant role of the thermodynamic activity of drugs in skin drug delivery. This thermodynamic activity works as a driving force for increasing/improving the absorption of drugs by the skin. It can be changed according to the physicochemical parameters (e.g., solubility, partition coefficient, and water activity) of the drug in the vehicle. Thermodynamic principles have been used for the development of novel topical and transdermal delivery systems, demonstrating the importance of thermodynamic activity in enhancing drug permeation through the skin. In this review, we provide insights into thermodynamic principles and their roles in optimizing topical and transdermal drug delivery systems.

Beneath the Skin: A Review of Current Trends and Future Prospects of Transdermal Drug Delivery Systems

The ideal drug delivery system has a bioavailability comparable to parenteral dosage forms but is as convenient and easy to use for the patient as oral solid dosage forms. In recent years, there has been increased interest in transdermal drug delivery (TDD) as a non-invasive delivery approach that is generally regarded as being easy to administer to more vulnerable age groups, such as paediatric and geriatric patients, while avoiding certain bioavailability concerns that arise from oral drug delivery due to poor absorbability and metabolism concerns. However, despite its many merits, TDD remains restricted to a select few drugs. The physiology of the skin poses a barrier against the feasible delivery of many drugs, limiting its applicability to only those drugs that possess physicochemical properties allowing them to be successfully delivered transdermally. Several techniques have been developed to enhance the transdermal permeability of drugs. Both chemical (e.g., thermal and mechanical) and passive (vesicle, nanoparticle, nanoemulsion, solid dispersion, and nanocrystal) techniques have been investigated to enhance the permeability of drug substances across the skin. Furthermore, hybrid approaches combining chemical penetration enhancement technologies with physical technologies are being intensively researched to improve the skin permeation of drug substances. This review aims to summarize recent trends in TDD approaches and discuss the merits and drawbacks of the various chemical, physical, and hybrid approaches currently being investigated for improving drug permeability across the skin.

Nanocrystal-based gel of apremilast ameliorates imiquimod-induced psoriasis by suppressing inflammatory responses

Apremilast is 'difficult-to-deliver' in stratum corneum and viable layers (viable epidermis, dermis) owing to its modest lipophilicity and poor aqueous solubility, respectively. The objective of the present research was to develop apremilast nanocrystal-based gel for enhanced anti-psoriatic efficacy for the treatment of psoriasis. Nanosuspension was generated by wet media milling with a mean particle size of 200 nm. In-vivoefficacy of nanocrystal-based gels was evaluated in the imiquimod-induced psoriatic plaque model. Nanocrystal-based gel (1% and 3% w/w) improved phenotypic, histopathological features of psoriatic skin and attenuated splenic hypertrophy, psoriasis area severity scoring. Enzyme-linked immunosorbent assay was performed to evaluate levels of psoriatic biochemical markers indicating a significant decrease in the concentration of cytokines such as IL-23, IL-17A, IL-6 and TNF-α by nanocrystal-based gels (1% and 3% w/w) over disease induced group. Skin irritation study revealed that nanocrystal-based gel was significantly less irritating than the positive control. These results suggest that nanocrystal-based gel of apremilast can be an effective strategy for the management of psoriasis.

Effect of Penetration Enhancers and Safety on the Transdermal Delivery of Apremilast in Skin

The poor water solubility of apremilast (APR) is the main impediment to the penetration of the drug through the skin barrier. The objective of this study was to evaluate the permeability of APR in different solutions enriched with penetration promoters in ex vivo samples of human skin, and additionally assess its tolerance in vivo. To this end, APR solutions with 5% promoter were developed, and the drug's ability to penetrate human abdominal skin samples was evaluated; the coefficients of permeability, cumulated amounts permeated, and flow were some of the parameters evaluated; likewise, the in vitro and in vivo tolerance of the solutions was evaluated. The results obtained showed that the solutions containing squalene as a promoter improved the penetration of APR compared to the other promoters evaluated; in the same way, on an in vitro scale in HaCaT cells, the promoters were not toxic, finding a cell viability greater than 80% at the different dilutions evaluated. In the in vivo tests carried out with the solution that presented the best results (APR-Squalene solution), it was observed that it does not cause irritation or erythema on the skin after its colorimetric and histological evaluation of the dorsal region of rats after its application. Squalene becomes an excellent candidate to improve the permeability of the drug in the case of the development of a topical formulation; in addition, it was confirmed that this penetration enhancer is neither toxic nor irritating when in contact with the skin in in vivo tests.

Assessing the Dermal Penetration Efficacy of Chemical Compounds with the Ex-Vivo Porcine Ear Model

(1) Background: The ex vivo porcine ear model is often used for the determination of the dermal penetration efficacy of chemical compounds. This study investigated the influence of the post-slaughter storage time of porcine ears on the dermal penetration efficacy of chemical compounds. (2) Methods: Six different formulations (curcumin and different fluorescent dyes in different vehicles and/or nanocarriers) were tested on ears that were (i) freshly obtained, (ii) stored for 24 or 48 h at 4 °C after slaughter before use and (iii) freshly frozen and defrosted 12 h before use. (3) Results: Results showed that porcine ears undergo post-mortem changes. The changes can be linked to rigor mortis and all other well-described phenomena that occur with carcasses after slaughter. The post-mortem changes modify the skin properties of the ears and affect the penetration efficacy. The onset of rigor mortis causes a decrease in the water-holding capacity of the ears, which leads to reduced penetration of chemical compounds. The water-holding capacity increases once the rigor is released and results in an increased penetration efficacy for chemical compounds. Despite different absolute penetration values, no differences in the ranking of penetration efficacies between the different formulations were observed between the differently aged ears. (4) Conclusions: All different types of ears can be regarded to be suitable for dermal penetration testing of chemical compounds. The transepidermal water loss (TEWL) and/or skin hydration of the ears were not correlated with the ex vivo penetration efficacy because both an impaired skin barrier and rigor mortis cause elevated skin hydration and TEWL values but an opposite penetration efficacy. Other additional values (for example, pH and/or autofluorescence of the skin) should, therefore, be used to select suitable and non-suitable skin areas for ex vivo penetration testing. Finally, data from this study confirmed that smartFilms and nanostructured lipid carriers (NLC) represent superior formulation strategies for efficient dermal and transdermal delivery of curcumin.

A Nanocrystals-Based Topical Drug Delivery System with Improved Dermal Penetration and Enhanced Treatment of Skin Diseases

Topical drug delivery methods are important in the treatment of skin diseases. Drug nanocrystals, which are nanometersized particles of active pharmaceutical ingredients, offer efficient topical delivery with high stability, high drug loading capacity, steady dissolution, and sustained drug release profiles. The use of nanocrystals for the topical delivery of skin disease therapies is currently being evaluated; this review focuses on how nanocrystals facilitate active pharmaceutical ingredient transport across skin barriers, exploring the underlying transportation mechanisms of the nanocrystals and active pharmaceutical ingredient molecules to the dermal and epidermal skin cells. In topical delivery, previous skin treatments, choice of excipients and vehicles, and penetration enhancement strategies critically influence the topical delivery of drug nanocrystals. Various research and applications of drug nanocrystals in skin disease therapy are highlighted in this review, and intellectual property protection for drug nanocrystal formulations, clinical trial data, and products with commercial potential are also discussed.

Pharmaceutical nanocrystals: A promising approach for improved topical drug delivery

The barrier function of skin and non-optimal physicochemical properties of drug present a challenge to skin penetration of many drugs, thus motivating the development of novel drug delivery systems. Recently, nanocrystal-based formulations have been investigated for topical drug delivery and demonstrated improved skin penetration. This review highlights barriers in skin penetration, current techniques to improve topical delivery and application of nanocrystals in conquering obstacles for topical delivery. Nanocrystals can improve delivery through the skin by mechanisms like higher concentration gradient across skin resulting in increased passive diffusion, hair follicle targeting, diffusional corona and adhesion to skin. This would be of interest for formulation scientists for product development of molecules that are 'difficult-to-deliver' topically.

Apremilast Microemulsion as Topical Therapy for Local Inflammation: Design, Characterization and Efficacy Evaluation

Apremilast (APR) is a selective phosphodiesterase 4 inhibitor administered orally in the treatment of moderate-to-severe plaque psoriasis and active psoriatic arthritis. The low solubility and permeability of this drug hinder its dermal administration. The purpose of this study was to design and characterize an apremilast-loaded microemulsion (APR-ME) as topical therapy for local skin inflammation. Its composition was determined using pseudo-ternary diagrams. Physical, chemical and biopharmaceutical characterization were performed. Stability of this formulation was studied for 90 days. Tolerability of APR-ME was evaluated in healthy volunteers while its anti-inflammatory potential was studied using in vitro and in vivo models. A homogeneous formulation with Newtonian behavior and droplets of nanometric size and spherical shape was obtained. APR-ME released the incorporated drug following a first-order kinetic and facilitated drug retention into the skin, ensuring a local effect. Anti-inflammatory potential was observed for its ability to decrease the production of IL-6 and IL-8 in the in vitro model. This effect was confirmed in the in vivo model histologically by reduction in infiltration of inflammatory cells and immunologically by decrease of inflammatory cytokines IL-8, IL-17A and TNFα. Consequently, these results suggest that this formulation could be used as an attractive topical treatment for skin inflammation.