Transdermal Delivery: Challenges and Opportunities

A special issue of Pharmaceutics (ISSN 1999-4923). This special issue belongs to the section "Drug Delivery and Controlled Release".

Deadline for manuscript submissions: closed (20 March 2025) | Viewed by 15160

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Guest Editor
Department of Pharmacy, Singidunum University, 11000 Belgrade, Serbia
Interests: skin delivery; dermal delivery; transdermal delivery; nanocarriers; liposomes; penetration enhancer
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Special Issue Information

Dear Colleagues,

The skin, being the largest organ in humans, which covers the whole body, has become recognized as an important drug delivery route. Unlike most other organs in the body, the skin can be reached directly. Therefore, there is a great interest in the skin as a site of drug application, both for dermal and transdermal drug delivery. Transdermal delivery involves the application of a drug to the skin in order to achieve systemically active drug levels to treat systemic diseases. Transdermal drug delivery systems (TDDS) offer a number of advantages compared to conventional drug delivery systems, leading to systemic drug effects. TDDS enable the drugs to be directly delivered to the systemic circulation, circumventing hepatic first-pass effects and avoiding the interaction of the drug with the gastrointestinal tract. Furthermore, TDDS act as a “depot”, controlling the rate of drug input over a prolonged period of time and ensuring constant plasma levels. Regarding drugs with a narrow therapeutic margin, their undesirable side effects, particularly those associated with pulsed peak plasma levels, may be reduced via the use of a TDDS. In addition, the use of a TDDS enables the dose frequency to be reduced. It is worth noting that TDDS are non-invasive, i.e., they avoid needle delivery, which is associated with pain and patient phobia (involved with intravenous therapy), and TDDS drugs can be self-administered. The aforementioned advantages of TDDS lead to enhanced patient compliance.

However, the effectiveness of transdermal drug delivery is often hindered by challenges such as the low permeability of the most apical layer of the skin, the stratum corneum, leading to limitations in the skin permeation of drugs and thus low therapeutic effectiveness due to the insufficient plasma levels of drugs. In addition, unfavorable drug properties such as inadequate solubility and partition coefficient (log P), as well as their high molecular weight values, limit the efficacy of transdermal drug delivery. Only few drug molecules yield skin permeability coefficients sufficiently high to develop clinically active plasma levels. Thus, the market for transdermal patches comprises patches with only few low-molecular-weight drugs.

Therefore, significant efforts have been devoted to developing strategies to overcome the impermeability of intact human skin, which provides the main barrier for drug penetration. These strategies involve chemical (formulation-based) and physical penetration enhancement techniques. Chemical penetration enhancement methods involve the manipulation of the drug or vehicle in order to enhance the drug diffusion through the skin; this also includes the use of different nanocarriers (e.g., vesicles, nanoparticles, etc.). Among physical methods, iontophoresis, electroporation, and ultrasound are the most studied enhancement methods.

The primary focus of this Special Issue is to address the opportunities and challenges associated with transdermal drug delivery and to demonstrate how various percutaneous penetration enhancement strategies can overcome these challenges, thereby improving the therapeutic efficacy of TDDS.

Dr. Nina Dragićević
Guest Editor

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Keywords

  • transdermal drug delivery
  • nanocarrier
  • iontophoresis
  • electroporation
  • ultrasound
  • liposome
  • nanoparticle

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Published Papers (6 papers)

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Research

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10 pages, 1104 KiB  
Article
Minocycline Nanocrystals: A New Approach for Treating Acne with Reduced Systemic Side Effects
by Suha M. Abudoleh, Juhaina M. Abu Ershaid, Dima Lafi, Nisreen A. Dahshan, Ahmad Talhouni and Amjad Abuirmeileh
Pharmaceutics 2025, 17(6), 727; https://doi.org/10.3390/pharmaceutics17060727 - 31 May 2025
Viewed by 263
Abstract
Background/Objectives: Acne vulgaris is a chronic skin infection characterized by high sebum secretion, keratosis around hair follicles, inflammation, and imbalance in androgen levels. Acne vulgaris causes permanent scars or skin pigmentation in cases of improper treatment. Oral or topical isotretinoin, contraceptives, and antibiotics [...] Read more.
Background/Objectives: Acne vulgaris is a chronic skin infection characterized by high sebum secretion, keratosis around hair follicles, inflammation, and imbalance in androgen levels. Acne vulgaris causes permanent scars or skin pigmentation in cases of improper treatment. Oral or topical isotretinoin, contraceptives, and antibiotics are used to treat acne. Minocycline is one of the widely used tetracyclines for this purpose; it inhibits the synthesis of proteins in bacterial ribosomes. Commonly, minocycline is prescribed daily for several months for acne vulgaris. Systemic minocycline is highly distributed into body fluids, and it is associated with several side effects and antibiotic resistance. Additionally, minocycline is highly metabolized in the liver, leading to reduced bioavailability upon systemic delivery. This study aims to develop and characterize minocycline nanocrystals for targeted skin delivery and evaluate their antimicrobial efficacy in treating acne vulgaris. Methods: Minocycline nanocrystals were synthesized using milling or solvent evaporation techniques. Nanocrystals were characterized in terms of particle size, particle distribution index (PDI), zeta potential, and morphology. The antibacterial efficacy against Propionibacterium acne, Staphylococcus aureus, and Staphylococcus epidermidis was evaluated using a minimum inhibitory concentration assay (MIC) and agar well diffusion test in comparison to coarse minocycline. Results: Minocycline nanocrystals had a particle size of 147.4 ± 7.8 nm and 0.27 ± 0.017 of PDI. The nanocrystals exhibited a loading efficiency of 86.19 ± 16.7%. Antimicrobial testing showed no significant difference in activity between minocycline and its nanoparticle formulation. In terms of skin deposition, the nanocrystals were able to deliver minocycline topically to rat skin significantly more than free minocycline. The nanocrystal solution deposited 554.56 ± 24.13 μg of minocycline into rat skin, whereas free minocycline solution deposited 373.99 ± 23.32 μg. Conclusions: Minocycline nanocrystals represent a promising strategy for targeted skin delivery in the treatment of acne vulgaris, potentially reducing systemic side effects and antibiotic resistance and improving patient outcomes. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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27 pages, 4866 KiB  
Article
Preparation and Evaluation of Tadalafil-Loaded Nanoemulgel for Transdermal Delivery in Cold-Induced Vasoconstriction: A Potential Therapy for Raynaud’s Phenomenon
by Shery Jacob, Jamila Ojochenemi Abdullahi, Shahnaz Usman, Sai H. S Boddu, Sohaib Naseem Khan, Mohamed A. Saad and Anroop B Nair
Pharmaceutics 2025, 17(5), 596; https://doi.org/10.3390/pharmaceutics17050596 - 1 May 2025
Viewed by 466
Abstract
Background/Objectives: Raynaud’s phenomenon (RP) is characterized by an exaggerated vasoconstrictive response of small blood vessels in the fingers and toes to cold or stress. Oral therapy with tadalafil (TDL), a phosphodiesterase-5 inhibitor, is limited by systemic side effects and reduced patient compliance. This [...] Read more.
Background/Objectives: Raynaud’s phenomenon (RP) is characterized by an exaggerated vasoconstrictive response of small blood vessels in the fingers and toes to cold or stress. Oral therapy with tadalafil (TDL), a phosphodiesterase-5 inhibitor, is limited by systemic side effects and reduced patient compliance. This study aimed to develop and evaluate a TDL-loaded nanoemulgel for transdermal delivery as a non-invasive treatment alternative for cold-induced vasoconstriction. Methods: TDL-loaded nanoemulsions were prepared using the aqueous titration method with cinnamon oil as the oil phase and Cremophor RH40 and Transcutol as the surfactant–cosurfactant system. The optimized nanoemulsion was incorporated into a carbopol-based gel to form a nanoemulgel. The formulation was characterized for droplet size, morphology, thermodynamic stability, rheological properties, in vitro drug release, skin permeation, and pharmacokinetic behavior. Infrared thermography was employed to assess in vivo efficacy in cold-induced vasoconstriction models. Results: The optimized TDL nanoemulsion exhibited a spherical morphology, a nanoscale droplet size, and an enhanced transdermal flux. The resulting nanoemulgel displayed suitable physicochemical and rheological properties for topical application, a short lag time (0.7 h), and a high permeability coefficient (Kp = 3.59 × 10−2 cm/h). Thermal imaging showed significant vasodilation comparable to standard 0.2% nitroglycerin ointment. Pharmacokinetic studies indicated improved transdermal absorption with a higher Cmax (2.13 µg/mL), a prolonged half-life (t1/2 = 16.12 h), and an increased AUC0–24 compared to an oral nanosuspension (p < 0.001). Conclusions: The developed TDL nanoemulgel demonstrated effective transdermal delivery and significant potential as a patient-friendly therapeutic approach for Raynaud’s phenomenon, offering an alternative to conventional oral therapy. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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24 pages, 4800 KiB  
Article
The Role of Natural Deep Eutectic Solvents in a Hydrogel Formulation Containing Lidocaine
by Feria Hasanpour, Mária Budai-Szűcs, Anita Kovács, Rita Ambrus, Orsolya Jójárt-Laczkovich, Boglárka Szalai, Branimir Pavlić, Péter Simon, Levente Törteli and Szilvia Berkó
Pharmaceutics 2025, 17(3), 324; https://doi.org/10.3390/pharmaceutics17030324 - 2 Mar 2025
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Abstract
Background/Objectives: This study investigates the use of natural deep eutectic solvents (NADESs) in enhancing the solubility and skin permeation of a lidocaine base, a lipophilic form, in hydrogel systems. The aim was to develop an environmentally sustainable and biocompatible alternative to conventional [...] Read more.
Background/Objectives: This study investigates the use of natural deep eutectic solvents (NADESs) in enhancing the solubility and skin permeation of a lidocaine base, a lipophilic form, in hydrogel systems. The aim was to develop an environmentally sustainable and biocompatible alternative to conventional lidocaine formulations, improving the dermal permeation and therapeutic efficacy. Methods: The lidocaine base was dissolved in a hydrophilic NADES system composed of choline chloride and citric acid, facilitating enhanced solubility, likely through new molecular interactions. Then, pH-adjusted hydrogels were formulated and optimized by employing a 32 full factorial design. Raman and nuclear magnetic resonance (NMR) spectroscopy were applied to evaluate the stability of lidocaine in the optimal formulation. The biopharmaceutical properties were investigated using in vitro drug release and skin permeation studies. In vivo tests assessed physiological skin parameters such as the hydration and transepidermal water loss. Results: The developed NADES-containing hydrogel significantly improved the solubility and stability of lidocaine. Skin permeation studies demonstrated enhanced dermal permeation compared with conventional hydrogel and ointment. These improvements, namely the enhanced solubility of lidocaine in the formulation and its increased permeation, were attributed to the dual effect of the NADES. Conclusions: NADES-containing hydrogels represent a promising green technology for formulating lidocaine-containing dermal preparations. This approach offers a biocompatible, natural-based alternative that can enhance the bioavailability and efficacy of topical anesthetics. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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29 pages, 7806 KiB  
Article
Formulation and Ex Vivo Evaluation of Ivermectin Within Different Nano-Drug Delivery Vehicles for Transdermal Drug Delivery
by Eunice Maureen Steenekamp, Wilna Liebenberg, Hendrik J. R. Lemmer and Minja Gerber
Pharmaceutics 2024, 16(11), 1466; https://doi.org/10.3390/pharmaceutics16111466 - 18 Nov 2024
Viewed by 2489
Abstract
Background/Objectives: Ivermectin gained widespread attention as the “miracle drug” during the coronavirus disease 2019 (COVID-19) pandemic. Its inclusion in the 21st World Health Organization (WHO) List of Essential Medicines is attributed to its targeted anti-helminthic response, high efficacy, cost-effectiveness and favorable safety profile. [...] Read more.
Background/Objectives: Ivermectin gained widespread attention as the “miracle drug” during the coronavirus disease 2019 (COVID-19) pandemic. Its inclusion in the 21st World Health Organization (WHO) List of Essential Medicines is attributed to its targeted anti-helminthic response, high efficacy, cost-effectiveness and favorable safety profile. Since the late 2000s, this bio-inspired active pharmaceutical ingredient (API) gained renewed interest for its diverse therapeutic capabilities. However, producing ivermectin formulations does remain challenging due to its poor water solubility, resulting in low bioavailability after oral administration. Therefore, the transdermal drug delivery of ivermectin was considered to overcome these challenges, which are observed after oral administration. Methods: Ivermectin was incorporated in a nano-emulsion, nano-emulgel and a colloidal suspension as ivermectin-loaded nanoparticles. The nano-drug delivery vehicles were optimized, characterized and evaluated through in vitro membrane release studies, ex vivo skin diffusion studies and tape-stripping to determine whether ivermectin was successfully released from its vehicle and delivered transdermally and/or topically throughout the skin. This study concluded with cytotoxicity tests using the methyl thiazolyl tetrazolium (MTT) and neutral red (NR) assays on both human immortalized epidermal keratinocytes (HaCaT) and human immortalized dermal fibroblasts (BJ-5ta). Results: Ivermectin was successfully released from each vehicle, delivered transdermally and topically throughout the skin and demonstrated little to no cytotoxicity at concentrations that diffused through the skin. Conclusions: The type of nano-drug delivery vehicle used to incorporate ivermectin influences its delivery both topically and transdermally, highlighting the dynamic equilibrium between the vehicle, the API and the skin. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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22 pages, 4338 KiB  
Article
Non-Invasive Delivery of Negatively Charged Nanobodies by Anodal Iontophoresis: When Electroosmosis Dominates Electromigration
by Phedra Firdaws Sahraoui, Oscar Vadas and Yogeshvar N. Kalia
Pharmaceutics 2024, 16(4), 539; https://doi.org/10.3390/pharmaceutics16040539 - 13 Apr 2024
Cited by 2 | Viewed by 2025
Abstract
Iontophoresis enables the non-invasive transdermal delivery of moderately-sized proteins and the needle-free cutaneous delivery of antibodies. However, simple descriptors of protein characteristics cannot accurately predict the feasibility of iontophoretic transport. This study investigated the cathodal and anodal iontophoretic transport of the negatively charged [...] Read more.
Iontophoresis enables the non-invasive transdermal delivery of moderately-sized proteins and the needle-free cutaneous delivery of antibodies. However, simple descriptors of protein characteristics cannot accurately predict the feasibility of iontophoretic transport. This study investigated the cathodal and anodal iontophoretic transport of the negatively charged M7D12H nanobody and a series of negatively charged variants with single amino acid substitutions. Surprisingly, M7D12H and its variants were only delivered transdermally by anodal iontophoresis. In contrast, transdermal permeation after cathodal iontophoresis and passive diffusion was <LOQ. The anodal iontophoretic delivery of these negatively charged proteins was achieved because electroosmosis was the dominant electrotransport mechanism. Cutaneous deposition after the anodal iontophoresis of M7D12HWT (wild type), and the R54E and K65E variants, was statistically superior to that after cathodal iontophoresis (6.07 ± 2.11, 9.22 ± 0.80, and 14.45 ± 3.45 μg/cm2, versus 1.12 ± 0.30, 0.72 ± 0.27, and 0.46 ± 0.07 µg/cm2, respectively). This was not the case for S102E, where cutaneous deposition after anodal and cathodal iontophoresis was 11.89 ± 0.87 and 8.33 ± 2.62 µg/cm2, respectively; thus, a single amino acid substitution appeared to be sufficient to impact the iontophoretic transport of a 17.5 kDa protein. Visualization studies using immunofluorescent labeling showed that skin transport of M7D12HWT was achieved via the intercellular and follicular routes. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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Review

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29 pages, 3207 KiB  
Review
Skin Structure, Physiology, and Pathology in Topical and Transdermal Drug Delivery
by Sofia Brito, Moonki Baek and Bum-Ho Bin
Pharmaceutics 2024, 16(11), 1403; https://doi.org/10.3390/pharmaceutics16111403 - 31 Oct 2024
Cited by 5 | Viewed by 7036
Abstract
Several industries are increasingly focused on enhancing the delivery of active ingredients through the skin to optimize therapeutic outcomes. By facilitating the penetration of active ingredients through the skin barrier, these enhancers can significantly improve the efficacy of various formulations, ranging from skincare [...] Read more.
Several industries are increasingly focused on enhancing the delivery of active ingredients through the skin to optimize therapeutic outcomes. By facilitating the penetration of active ingredients through the skin barrier, these enhancers can significantly improve the efficacy of various formulations, ranging from skincare products to therapeutic agents targeting systemic circulation. As the understanding of skin physiology and the mechanisms of drug absorption deepen, these industries are adopting permeation enhancers more widely, ultimately leading to better patient outcomes and expanded treatment options. However, the structure and physiological function of the skin can vary according to different factors, such as the area of the body and between individuals. These variations, along with external environmental exposures, aging and pathological conditions, introduce complexities that must be carefully considered when designing effective delivery systems. Considering the intricacies of skin structure and physiology, tailoring systems to account for regional differences, individual variability, and changes induced by environmental factors or disease is critical to optimizing therapeutic outcomes. This review discusses the features of skin structure, physiology, and pathologies, as well as the application of permeation enhancers in these contexts. Furthermore, it addresses the use of animal skin models in transdermal delivery and dermatological studies, along with the latest developments in this field. Full article
(This article belongs to the Special Issue Transdermal Delivery: Challenges and Opportunities)
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