Essential Fatty Acids as Transdermal Penetration Enhancers

Co-Processed Crystalline Solids of Ivermectin with Span® 60 as Solubility Enhancers of Ivermectin in Natural Oils

Despite being discovered over five decades ago, little is still known about ivermectin. Ivermectin has several physico-chemical properties that can result in it having poor bioavailability. In this study, polymorphic and co-crystal screening was used to see if such solid-state modifications can improve the oil solubility of ivermectin. Span® 60, a lipophilic non-ionic surfactant, was chosen as co-former. The rationale behind attempting to improve oil solubility was to use ivermectin in future topical and transdermal preparations to treat a range of skin conditions like scabies and head lice. Physical mixtures were also prepared in the same molar ratios as the co-crystal candidates, to serve as controls. Solid-state characterization was performed using X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR spectra of the co-crystal candidates showed the presence of Span® 60's alkyl chain peaks, which were absent in the spectra of the physical mixtures. Due to the absence of single-crystal X-ray data, co-crystal formation could not be confirmed, and therefore these co-crystal candidates were referred to as co-processed crystalline solids. Following characterization, the solid-state forms, physical mixtures and ivermectin raw material were dissolved in natural penetration enhancers, i.e., avocado oil (AVO) and evening primrose oil (EPO). The co-processed solids showed increased oil solubility by up to 169% compared to ivermectin raw material. The results suggest that co-processing of ivermectin with Span® 60 can be used to increase its oil solubility and can be useful in the development of oil-based drug formulations.

Recent advances in delivery of transdermal nutrients: A review

Nutrients provide vital functions in the body for sustained health, which have been shown to be related to the incidence, prevention and treatment of disease. However, limited bioavailability, loss of targeting specificity and the increased hepatic metabolism limit the utilization of nutrients. In this review, we highlight transdermal absorption of nutrients, which represents an opportunity to allow great use of many nutrients with promising human health benefits. Moreover, we describe how the various types of permeation enhancers are increasingly exploited for transdermal nutrient delivery. Chemical penetration enhancers, carrier systems and physical techniques for transdermal nutrient delivery are described, with a focus on combinatorial approaches. Although there are many carrier systems and physical techniques currently in development, with some tools currently in advanced clinical trials, relatively few products have achieved full translation to clinical practice. Challenges and further developments of these tools are discussed here in this review. This review will be useful to researchers interested in transdermal applications of permeation enhancers for the efficient delivery of nutrients, providing a reference for supporting the need to take more account of specific nutritional needs in specific states.

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.

Anti-ageing peptides and proteins for topical applications: a review

Skin ageing is a cumulative result of oxidative stress, predominantly caused by reactive oxygen species (ROS). Respiration, pollutants, toxins, or ultraviolet A (UVA) irradiation produce ROS with 80% of skin damage attributed to UVA irradiation. Anti-ageing peptides and proteins are considered valuable compounds for removing ROS to prevent skin ageing and maintenance of skin health. In this review, skin ageing theory has been illustrated with a focus on the mechanism and relationship with anti-ageing peptides and proteins. The effects, classification, and transport pathways of anti-ageing peptides and proteins across skin are summarized and discussed. Over the last decade, several novel formulations and advanced strategies have been developed to overcome the challenges in the dermal delivery of proteins and peptides for skin ageing. This article also provides an in-depth review of the latest advancements in the dermal delivery of anti-ageing proteins and peptides. Based on these studies, this review prospected several semi-solid dosage forms to achieve topical applicability for anti-ageing peptides and proteins.

The Monoterpenoid Perillyl Alcohol: Anticancer Agent and Medium to Overcome Biological Barriers

Perillyl alcohol (POH) is a naturally occurring monoterpenoid related to limonene that is present in the essential oils of various plants. It has diverse applications and can be found in household items, including foods, cosmetics, and cleaning supplies. Over the past three decades, it has also been investigated for its potential anticancer activity. Clinical trials with an oral POH formulation administered to cancer patients failed to realize therapeutic expectations, although an intra-nasal POH formulation yielded encouraging results in malignant glioma patients. Based on its amphipathic nature, POH revealed the ability to overcome biological barriers, primarily the blood–brain barrier (BBB), but also the cytoplasmic membrane and the skin, which appear to be characteristics that critically contribute to POH’s value for drug development and delivery. In this review, we present the physicochemical properties of POH that underlie its ability to overcome the obstacles placed by different types of biological barriers and consequently shape its multifaceted promise for cancer therapy and applications in drug development. We summarized and appraised the great variety of preclinical and clinical studies that investigated the use of POH for intranasal delivery and nose-to-brain drug transport, its intra-arterial delivery for BBB opening, and its permeation-enhancing function in hybrid molecules, where POH is combined with or conjugated to other therapeutic pharmacologic agents, yielding new chemical entities with novel mechanisms of action and applications.

Molecular perspective of efficiency and safety problems of chemical enhancers: bottlenecks and recent advances

Chemical penetration enhancer (CPE) is a preferred approach to improve drug permeability through the skin, due to its unique advantages of simple use and high compatibility. However, CPEs efficiency and safety problems frequently arise, which greatly restrains the further application in transdermal drug delivery systems (TDDS). To get access to the root of problems, the efficiency and safety of CPEs are reviewed especially from molecular perspectives, which include (1) the possible factors of CPEs low efficiency; (2) the possible contribution of CPEs in the evolution of safety problems such as skin irritation and allergic reaction; (3) the interactive relationship between CPEs efficiency and safety, as well as the bottlenecks of achieving their balance. More importantly, based on these, recent advances are summarized in improving efficiency or safety of CPEs, which offers a guidance of rationally selecting CPEs in future research.

Comparative efficacy evaluation of different penetration enhancement strategies for dermal delivery of poorly soluble drugs - A case with sertaconazole nitrate

The aim of this study was to compare the efficacy of different approaches for enhancement of dermal availability of the highly lipophilic antifungal model drug - sertaconazole nitrate (SN). For this purpose, a physical penetration enhancer - dissolving microneedles (MNs) was fabricated by filling moulds with liquid formulation based on polyvinylpyrrolidone and loaded with SN. Dissolving MNs were characterised regarding their morphological and mechanical characteristics. A penetration enhancement efficacy of MNs was evaluated in vitro using porcine ear skin in parallel with the efficacy of formerly developed chemical penetration enhancer - biocompatible microemulsion (ME) formulation. Moreover, an ability of solid silicon MNs to significantly improve delivery of SN from ME into the skin has also been investigated. The obtained results showed that dissolving MNs had satisfying morphological properties and mechanical strength. This type of MNs provided comparable drug deposition in the skin as ME formulation, but also revealed an indication of percutaneous absorption of a portion of the administered drug dose. However, the penetration/permeation study results were largely influenced by experimental setup and dosing regimen. Although solid silicon MNs assisted SN dermal delivery led to increase of drug cutaneous retention (1.9-fold) under infinite dosing regimen, the synergistic action of solid MNs and ME applied under finite dosing was more pronounced in comparison with the application either of physical (dissolving MNs) or chemical enhancer (ME) alone. Namely, SN amount accumulated into the skin increased up to 4.67 and 4.37 folds in comparison with ME and dissolving MNs alone, respectively, while reaching a significant decrease in drug permeation through the skin compared to the use of dissolving MNs. Application of ME per se was the only approach that provided selective in vitro dermal drug delivery without SN permeation across the skin. However, despite both types of the used MNs lead to SN permeation in vitro, the ratio between the drug amount deposited in the skin and SN content permeated was significantly higher for the combined approach (12.05) than for dissolving MNs (2.10). Therefore, a combination of solid silicon MNs and biocompatible ME favoured more pronouncedly SN skin accumulation, which is preferable in the treatment of skin fungal infections.

Emerging skin-targeted drug delivery strategies to engineer immunity: A focus on infectious diseases

INTRODUCTION

Infectious pathogens are global disrupters. Progress in biomedical science and technology has expanded the public health arsenal against infectious diseases. Specifically, vaccination has reduced the burden of infectious pathogens. Engineering systemic immunity by harnessing the cutaneous immune network has been particularly attractive since the skin is an easily accessible immune-responsive organ. Recent advances in skin-targeted drug delivery strategies have enabled safe, patient-friendly, and controlled deployment of vaccines to cutaneous microenvironments for inducing long-lived pathogen-specific immunity to mitigate infectious diseases, including COVID-19.

AREAS COVERED

This review briefly discusses the basics of cutaneous immunomodulation and provides a concise overview of emerging skin-targeted drug delivery systems that enable safe, minimally invasive, and effective intracutaneous administration of vaccines for engineering systemic immune responses to combat infectious diseases.

EXPERT OPINION

In-situ engineering of the cutaneous microenvironment using emerging skin-targeted vaccine delivery systems offers remarkable potential to develop diverse immunization strategies against pathogens. Mechanistic studies with standard correlates of vaccine efficacy will be important to compare innovative intracutaneous drug delivery strategies to each other and to existing clinical approaches. Cost-benefit analyses will be necessary for developing effective commercialization strategies. Significant involvement of industry and/or government will be imperative for successfully bringing novel skin-targeted vaccine delivery methods to market for their widespread use.

Enhancement strategies for transdermal drug delivery systems: current trends and applications

Transdermal drug delivery systems have become an intriguing research topic in pharmaceutical technology area and one of the most frequently developed pharmaceutical products in global market. The use of these systems can overcome associated drawbacks of other delivery routes, such as oral and parenteral. The authors will review current trends, and future applications of transdermal technologies, with specific focus on providing a comprehensive understanding of transdermal drug delivery systems and enhancement strategies. This article will initially discuss each transdermal enhancement method used in the development of first-generation transdermal products. These methods include drug/vehicle interactions, vesicles and particles, stratum corneum modification, energy-driven methods and stratum corneum bypassing techniques. Through suitable design and implementation of active stratum corneum bypassing methods, notably microneedle technology, transdermal delivery systems have been shown to deliver both low and high molecular weight drugs. Microneedle technology platforms have proven themselves to be more versatile than other transdermal systems with opportunities for intradermal delivery of drugs/biotherapeutics and therapeutic drug monitoring. These have shown that microneedles have been a prospective strategy for improving transdermal delivery systems.

Unconventional Passive Enhancement of Transdermal Drug Delivery: toward a Mechanistic Understanding of Penetration Enhancers Releasing from Acrylic Pressure-Sensitive Adhesive of Patches

PURPOSE

Penetration enhancers (PEs) enhancing efficacy depends on two processes: PEs release from patches and action on skin. Compared with their action on skin, PEs release process was poorly understood. Therefore, the purpose of this study was to make a mechanistic understanding of PEs release from acrylic pressure-sensitive adhesive of patches and propose an unconventional enhancement of PEs efficacy.

METHODS

PEs efficacy was evaluated both in drug permeation study and drug pharmacokinetic study. Confocal Raman spectroscopy was employed to observe PEs release behavior by mapping PEs dynamic distribution in skin. The mechanism of PEs release behavior was provided from molecular interaction and rheology using FT-IR, molecular docking, molecular dynamic simulation and rheometer, separately.

RESULTS

The release behavior of PEs themselves greatly restricted their efficacy. By using PEG 400, an improvement of oleic acid (OA) release behavior was achieved, and the efficacy of OA was significantly enhanced with enhancing ratio (ER) from 2.69 to 4.10 and AUC_last from 1574 ± 87 to 2664 ± 249 ng·h/mL, separately. The improvement of OA release behavior was primarily resulted from reduction of the interaction between OA and adhesive, which was caused by other small molecules with a strong ability in forming hydrogen bonds with adhesive. Also, the rigidity of adhesive was a factor in affecting PEs release behavior.

CONCLUSIONS

An unconventional passive enhancement of transdermal drug delivery was achieved via improving PEs themselves releasing from acrylic pressure-sensitive adhesive. Graphical abstract Influence of PEs release behavior on drug permeation through skin and molecular mechanism.

Development of a Self-Emulsifying Drug Delivery System for Optimized Topical Delivery of Clofazimine

A quality-by-design and characterization approach was followed to ensure development of self-emulsifying drug delivery systems (SEDDSs) destined for topical delivery of the highly lipophilic clofazimine. Solubility and water-titration experiments identified spontaneous emulsification capacity of different excipient combinations and clofazimine. After identifying self-emulsification regions, check-point formulations were selected within the self-emulsification region by considering characteristics required to achieve optimized topical drug delivery. Check-point formulations, able to withstand phase separation after 24 h at an ambient temperature, were subjected to characterization studies. Experiments involved droplet size evaluation; size distribution; zeta-potential; self-emulsification time and efficacy; viscosity and pH measurement; cloud point assessment; and thermodynamic stability studies. SEDDSs with favorable properties, i.e., topical drug delivery, were subjected to dermal diffusion studies. Successful in vitro topical clofazimine delivery was observed. Olive oil facilitated the highest topical delivery of clofazimine probably due to increased oleic acid levels that enhanced stratum corneum lipid disruption, followed by improved dermal clofazimine delivery. Finally, isothermal microcalometric experiments studied the compatibility of excipients. Potential interactions were depicted between argan oil and clofazimine as well as between Span®60 and argan-, macadamia- and olive oil, respectively. However, despite some mundane incompatibilities, successful development of topical SEDDSs achieved enhanced topical clofazimine delivery.

Development of Topical/Transdermal Self-Emulsifying Drug Delivery Systems, Not as Simple as Expected

Self-emulsifying drug delivery systems (SEDDSs) originated as an oral lipid-based drug delivery system with the sole purpose of improving delivery of highly lipophilic drugs. However, the revolutionary drug delivery possibilities presented by these uniquely simplified systems in terms of muco-adhesiveness and zeta-potential changing capacity lead the way forward to ground-breaking research. Contrarily, SEDDSs destined for topical/transdermal drug delivery have received limited attention. Therefore, this review is focused at utilising principles, established during development of oral SEDDSs, and tailoring them to fit evaluation strategies for an optimised topical/transdermal drug delivery vehicle. This includes a detailed discussion of how the authentic pseudo-ternary phase diagram is employed to predict phase behaviour to find the self-emulsification region most suitable for formulating topical/transdermal SEDDSs. Additionally, special attention is given to the manner of characterising oral SEDDSs compared to topical/transdermal SEDDSs, since absorption within the gastrointestinal tract and the multi-layered nature of the skin are two completely diverse drug delivery territories. Despite the advantages of the topical/transdermal drug administration route, certain challenges such as the relatively undiscovered field of skin metabolomics as well as the obstacles of choosing excipients wisely to establish skin penetration enhancement might prevail. Therefore, development of topical/transdermal SEDDSs might be more complicated than expected.

Distinct Influence of Saturated Fatty Acids on Malignant and Nonmalignant Human Lung Epithelial Cells

The impact of saturated fatty acids (FA) on viability and properties of malignant and nonmalignant cells has not been studied in detail so far. The present study was aimed at evaluation of the influence of saturated FA (10:0-18:0) on malignant (A459) and nonmalignant (BEAS-2B) human lung epithelial cells. FA strongly affected A549 cells, but not BEAS-2B cells. Viability of A549 cells incubated with 14:0-18:0 was decreased by 53-91% as compared to untreated cells. Cell membrane stiffness in those cells as measured by atomic force microscopy was also reduced. Median value of apparent Young's modulus of untreated A549 cell membrane was 16.9 kPa and it decreased to 8.9 kPa for cells incubated with 14:0. Viability and mechanical properties of BEAS-2B cells were not altered by presence of FA. Those surprising discrepancies can be related to the differences in FA uptake rate. A549 cells were found to incorporate higher amount of FA and this corresponded to decrease in cell membrane stiffness and reduced cell viability. The performed studies showed that saturated FA have distinct influence on various types of cells, which may be exploited in development of the advanced lipid drug delivery systems.

Development of galangal essential oil-based microemulsion gel for transdermal delivery of flurbiprofen: simultaneous permeability evaluation of flurbiprofen and 1,8-cineole

Flurbiprofen (FP) is one of the most potent nonsteroidal anti-inflammatory drugs with very low bioavailability of approximately 12% following transdermal administration, compared to that after oral administration. This study aimed to deliver FP as a microemulsion (ME) gel by transdermal administration. Galangal essential oil (GEO) was extracted from Rhizoma Alpiniae Officinarum and identified by GC-MS. The most abundant constituent was determined to be 1,8-cineole (52.06%). Compared to azone, GEO was proved to exert significantly higher (p < .01) penetration enhancement effect and significantly (p < .001) lower skin cell toxicity. The formulation (FP-GEO-ME gel) was prepared using GEO as an oil phase and a penetration enhancer. Compared to that of FP solution, the enhancement ratio (ER) of FP-GEO-ME gel was 4.06. In addition, more than 25% 1,8-cineole permeated through the rat skin. In vivo pharmacokinetic studies revealed that the AUC_0-t of FP after transdermal administration of FP-GEO-ME gel was higher by approximately 4.56-fold than that of marketed FP cataplasms. The relative bioavailability of FP and 1,8-cineole after transdermal administration compared to oral administration of FP-GEO-ME were determined to be 96.58% and 85.49%, respectively. FP-GEO-ME gel significantly inhibited carrageenan-induced hind-paw edema and decreased PGE2 levels in rat serum. GEO-ME gel also exhibited significant anti-inflammatory effects at 2 h after the therapy (p < .05). The synergistic effects of FP and GEO were expected for the application of FP-GEO-ME gel. In conclusion, GEO-ME gel may be a promising formulation for transdermal administration of anti-inflammatory hydrophobic drugs, such as FP.

Topical Delivery of Niacinamide: Influence of Binary and Ternary Solvent Systems

Niacinamide (NIA) is the amide form of vitamin B3 and has been widely used in pharmaceutical and personal care formulations. Previously, we reported a comparative study of NIA permeation from neat solvents using the Skin Parallel Artificial Membrane Permeability Assay (PAMPA) and mammalian skin. A good correlation between NIA permeation in the different models was found. In the present work, ten binary and ternary systems were evaluated for their ability to promote NIA delivery in the Skin PAMPA model, porcine skin and human epidermis. Penetration enhancement was evident for binary systems composed of propylene glycol and fatty acids in human skin studies. However, propylene glycol and oleic acid did not promote enhancement of NIA compared with other systems in the Skin PAMPA model. A good correlation was obtained for permeation data from Skin PAMPA and porcine skin. However, data from the Skin PAMPA model and from human skin could only be correlated when the PG-fatty acid systems were excluded. These findings add to our knowledge of the potential applications of Skin PAMPA for screening dermal/transdermal preparations.

Effect of Chemical Permeation Enhancers on Skin Permeability: In silico screening using Molecular Dynamics simulations

Breaching of the skin barrier is essential for delivering active pharmaceutical ingredients (APIs) for pharmaceutical, dermatological and aesthetic applications. Chemical permeation enhancers (CPEs) are molecules that interact with the constituents of skin’s outermost and rate limiting layer stratum corneum (SC), and increase its permeability. Designing and testing of new CPEs is a resource intensive task, thus limiting the rate of discovery of new CPEs. In-silico screening of CPEs in a rigorous skin model could speed up the design of CPEs. In this study, we performed coarse grained (CG) molecule dynamics (MD) simulations of a multilayer skin lipid matrix in the presence of CPEs. The CPEs are chosen from different chemical functionalities including fatty acids, esters, and alcohols. A multi-layer in-silico skin model was developed. The CG parameters of permeation enhancers were also developed. Interactions of CPEs with SC lipids was studied in silico at three different CPE concentrations namely, 1% w/v, 3% w/v and 5% w/v. The partitioning and diffusion coefficients of CPEs in the SC lipids were found to be highly size- and structure-dependent and these dependencies are explained in terms of structural properties such as radial distribution function, area per lipid and order parameter. Finally, experimentally reported effects of CPEs on skin from the literature are compared with the simulation results. The trends obtained using simulations are in good agreement with the experimental measurements. The studies presented here validate the utility of in-silico models for designing, screening and testing of novel and effective CPEs.

Topical Delivery of Artemisone, Clofazimine and Decoquinate Encapsulated in Vesicles and Their In vitro Efficacy Against Mycobacterium tuberculosis

Vesicles are widely investigated as carrier systems for active pharmaceutical ingredients (APIs). For topical delivery, they are especially effective since they create a "depot-effect" thereby concentrating the APIs in the skin. Artemisone, clofazimine and decoquinate were selected as a combination therapy for the topical treatment of cutaneous tuberculosis. Delivering APIs into the skin presents various challenges. However, utilising niosomes, liposomes and transferosomes as carrier systems may circumvent these challenges. Vesicles containing 1% of each of the three selected APIs were prepared using the thin-film hydration method. Isothermal calorimetry, differential scanning calorimetry and hot-stage microscopy indicated no to minimal incompatibility between the APIs and the vesicle components. Encapsulation efficiency was higher than 85% for all vesicle dispersions. Vesicle stability decreased and size increased with an increase in API concentration; and ultimately, niosomes were found the least stable of the different vesicle types. Skin diffusion studies were subsequently conducted for 12 h on black human female skin utilising vertical Franz diffusion cells. Transferosomes and niosomes delivered the highest average concentrations of clofazimine and decoquinate into the skin, whereas artemisone was not detected and no APIs were present in the receptor phase. Finally, efficacy against tuberculosis was tested against the Mycobacterium tuberculosis H37Rv laboratory strain. All the dispersions depicted some activity, surprisingly even the blank vesicles portrayed activity. However, the highest percentage inhibition (52%) against TB was obtained with niosomes containing 1% clofazimine.

The Influence of Solid Microneedles on the Transdermal Delivery of Selected Antiepileptic Drugs

The aim of this project was to examine the effect of microneedle rollers on the percutaneous penetration of tiagabine hydrochloride and carbamazepine across porcine skin in vitro. Liquid chromatography-mass spectrometric analysis was carried out using an Agilent 1200 Series HPLC system coupled to an Agilent G1969A TOF-MS system. Transdermal flux values of the drugs were determined from the steady-state portion of the cumulative amount versus time curves. Following twelve hours of microneedle roller application, there was a 6.74-fold increase in the percutaneous penetration of tiagabine hydrochloride (86.42 ± 25.66 µg/cm²/h) compared to passive delivery (12.83 ± 6.30 µg/cm²/h). For carbamazepine in 20% ethanol, passive transdermal flux of 7.85 ± 0.60 µg/cm²/h was observed compared to 10.85 ± 0.11 µg/cm²/h after microneedle treatment. Carbamazepine reconstituted in 30% ethanol resulted in only a 1.19-fold increase in drug permeation across porcine skin (36.73 ± 1.83 µg/cm²/h versus 30.74 ± 1.32 µg/cm²/h). Differences in flux values of untreated and microneedle-treated porcine skin using solid microneedles for the transdermal delivery of tiagabine were statistically significant. Although there were 1.38- and 1.19-fold increases in transdermal flux values of carbamazepine when applied as 20% and 30% ethanol solutions across microneedle-treated porcine skin, respectively, the increases were not statistically significant.

Recent trends in the transdermal delivery of therapeutic agents used for the management of neurodegenerative diseases

With the increasing proportion of the global geriatric population, it becomes obvious that neurodegenerative diseases will become more widespread. From an epidemiological standpoint, it is necessary to develop new therapeutic agents for the management of Alzheimer's disease, Parkinson's disease, multiple sclerosis and other neurodegenerative disorders. An important approach in this regard involves the use of the transdermal route. With transdermal drug delivery systems (TDDS), it is possible to modulate the pharmacokinetic profiles of these medications and improve patient compliance. Transdermal drug delivery has also been shown to be useful for drugs with short half-life and low or unpredictable bioavailability. In this review, several transdermal drug delivery enhancement technologies are being discussed in relation to the delivery of medications used for the management of neurodegenerative disorders.