Investigation of the permeation enhancer strategy on benzoylaconitine transdermal patch: the relationship between transdermal enhancement strength and physicochemical properties of permeation enhancer

Transdermal Drug Delivery Systems (TDDS): Recent Advances and Failure Modes

Transdermal drug delivery systems (TDDS), commonly refered to as "patches", present a nonintrusive technique to provide medication without the need for invasive procedures. These products adhere to the skin and gradually release a specific dosage of medicine at a defined rate into the bloodstream. Compared with other methods of drug delivery, TDDS offer benefits such as reduced invasiveness, convenience for patients, and avoidance of the metabolic processes that occur when drugs are orally consumed. Throughout time, TDDS have been used to provide medications for various medical conditions (such as nicotine, fentanyl, nitroglycerin, and clonidine), and their potential for delivering biologics is currently being explored. This review investigates the current literature on the drug delivery efficacy of medical TDDS through the transdermal route. Additionally, the review addresses potential risks and failure modes associated with TDDS design and development as well as strategies for mitigating such risks. A thorough understanding of failure modes provides a blueprint to mitigate failure and produce high-quality efficacious therapeutics.

Ternary Deep Eutectic Solvents System of Colchicine, 4-Hydroxyacetophenone, and Protocatechuic Acid and Characterization of Transdermal Enhancement Mechanism

This study aimed to prepare colchicine (CO), 4-hydroxyacetophenone (HA), and protocatechuic acid (CA) contained in transdermal rubber plasters into a more releasable and acrylate pressure-sensitive adhesive (PSA) to optimize traditional Touguling rubber plasters (TOU) with enhanced transdermal permeability by using deep eutectic solvents (DES) technology. We compared the difference in the release behavior of CO between rubber plaster and PSA, determined the composition of the patch through pharmacodynamic experiments, explored the transdermal behavior of the three components, optimized the patch formula factors, and improved the penetration of CO through the skin. We also focused on elucidating the interactions among the three components of DES and the intricate relationship between DES and the skin. The melting point of DES was determined using DSC, while FTIR, 13C NMR, and ATR-FTIR were used to explore the intricate molecular mechanisms underlying the formation of DES, as well as its enhancement of skin permeability. The results of this investigation confirmed the successful formation of DES, marked by a discernible melting point at 27.33°C. The optimized patch, formulated with a molar ratio of 1:1:1 for CO, HA, and CA, significantly enhanced skin permeability, with the measured skin permeation quantities being 32.26 ± 2.98 µg/cm2, 117.67 ± 7.73 µg/cm2, and 56.79 ± 1.30 µg/cm2 respectively. Remarkably, the optimized patch also demonstrated similar analgesic and anti-inflammatory effects compared to commercial diclofenac diethylamide patches in different pharmacodynamics studies. The formation of DES altered drug compatibility with skin lipids and increased retention, driven by the interaction among the three component molecules through hydrogen bonding, effectively shielding the skin-binding sites and enhancing component permeation. In summary, the study demonstrated that optimized DES patches can concurrently enhance the penetration of CO, HA, and CA, thereby providing a promising approach for the development of DES in transdermal drug delivery systems. The findings also shed light on the molecular mechanisms underlying the transdermal behavior of DES and offer insights for developing more effective traditional Chinese medicine transdermal drug delivery systems.

Formulation Development and Molecular Mechanism Characterization of Long-Acting Patches of Asenapine for Efficient Delivery by Combining API-ILs Strategy and Controlled-Release Polymers

The objective of our study, which combined API-ILs strategy and controlled-release polymers, was to prepare a 72 h long-acting drug-in-adhesive patch for optimum delivery of asenapine (ASE). Special attention was paid to the permeation promotion mechanism and the controlled release behavior of ASE-ILs in pressure sensitive adhesives (PSA). Formulation factors were investigated by ex vivo transdermal experiments. The optimized patch was evaluated by pharmacokinetics study and skin irritation test. The obtained formulation was as follows, 15% w/w ASE-MA (about 1136 μg/cm2 ASE, 413 μg/cm2 MA), AACONH2 (Amide adhesive) as the matrix, 80 μm thickness, backing film of CoTran™ 9733. The optimized patch displayed satisfactory ex vivo and in vivo performance with Q 72 h of 620 ± 44 µg/cm2 and Fabs of 62.4%, which utilization rate (54.6%) was significantly higher than the control group (38.3%). By using the classical shake flask method, 13C NMR, DSC, and FTIR, the physicochemical properties and structure of ILs were characterized. log Do/w, ATR-FTIR, Raman, and molecular dynamics simulation results confirmed that ASE-MA (MA: 3-Methoxypropionic acid) had appropriate lipophilicity, and affected lipid fluidity as well as the conformation of keratin to improve the skin permeation. The FTIR, MDSC, rheology, and molecular docking results revealed that hydrogen bond (H-bond), were formed between ASE-MA and PSA, and the drug increased the molecular mobility of polymer chains. In summary, the 72 h long-acting patch of ASE was successfully prepared and it supplied a reference for the design of long-acting patches with ASE.

Development and Characterisation of a Topical Methyl Salicylate Patch: Effect of Solvents on Adhesion and Skin Permeation

The advent of skin patch formulation design and technology has enabled the commercialisation of methyl salicylate (MS) as a topical patch. However, the most fundamental aspect of skin permeation is unknown at present. The study aims to investigate the effect of solvent choice on the skin permeation of MS in a neat solvent system and patch formulation with an emphasis on patch adhesion. MS in six selected solvents (propylene glycol (PG), Transcutol^®, isopropyl myristate, Labrasol^®, Plurol^® oleique CC 497 and Maisine^® CC) was characterised and in vitro permeation studies were also performed. An ATR-FTIR analysis on solvent-treated skin was conudcted. Patch formulation was prepared and characterised for adhesion, in vitro drug release and skin permeation studies. The highest MS permeation was found in neat PG over 24 h (~90 μg/cm²) due to its strong skin protein conformation effect. Transcutol^® and isopropyl myristate showed better skin deposition and formulation retention, respectively. Nevertheless, PG enhanced the patch adhesion despite having a lower cumulative amount of MS permeated (~80 μg/cm²) as compared with Transcutol^® and Maisine^® (~110-150 μg/cm²). These two solvents, however, demonstrated better skin deposition and formulation retention but a lower patch adhesion. The unpredictable influence of the solvent on patch adhesion highlights the importance of the trade-off between patch adhesion and skin permeation during formulation design.

Design of a Long-Acting Rivastigmine Transdermal Delivery System: Based on Computational Simulation

The purpose of our study was using a computational simulation to develop a long-acting patch of rivastigmine (RVS). A range of patch formulations were screened including pressure sensitive adhesive (PSA), pharmaceutical excipients, and controlled release membranes using transfer simulation based on a mathematical model. Diffusion dynamics parameters for simulated operations were acquired through in vitro release tests (IVRT) and in vitro skin permeation tests (IVPT). The mechanism of controlled release was studied by FTIR (Fourier transform infrared), DSC (differential scanning calorimeter) and molecular docking. Results of a rat in vitro permeation profile showed excellent correlation with the in vivo deconvolution profile (R²=0.998). Experiments testified to transfer of RVS at a relatively uniform speed with high skin permeation (2531.2±142.46 μg/cm²) in 72 h. Pharmacokinetic data obtained in vivo also confirmed stable plasma concentrations over 72 h for the optimized patch, and significant prolongation of both T_max (11.20±1.79 h) and MRT_0-t (33.91±5.33 h). C_max was controlled with AUC_0-t (267.34±24.46 h ng/ml), which was closely comparable to parameters of a commercial Exelon® Patch. The successful development of a long-acting patch of RVS thus underscores the potential of computer aided design in a context of promnesic transdermal delivery. Graphical abstract.

A molecular mechanism investigation of the transdermal/topical absorption classification system on the basis of drug skin permeation and skin retention

A transdermal/topical absorption classification system for the characterization of the systemic or local delivery of drugs is the theoretical basis for the design and evaluation of transdermal/topical formulations. A classification system was established on the basis of the in vitro and in vivo skin permeation/retention behaviors of 12 model drugs. Drug skin penetration/retention exhibited a significant correlation with physicochemical parameters (log K_O/W, molecular weight, polar surface area, and polarizability). Four representative model drugs were selected to clarify the molecular mechanisms of drug skin permeation/retention behaviors. The excellent lipid-disrupting effect and enhanced partitioning exhibited by propranolol (high permeation-high retention) and zolmitriptan (high permeation-low retention) via the formation of moderate H-bonds with skin lipids were proven by ATR-FTIR (Δν_asCH2 > 2 cm^-1), Raman spectra (ΔLPP, SPP > 0.2 nm), and X-ray scattering (lipid crystallization) and were supported by ¹³C NMR results. The low lipid miscibility of zolmitriptan (ΔH_{zolmitriptan-lipid} = 126.92 J/g) caused the low skin retention of this drug. High polarizabiltiy (α = 38.5 × 10^-24 cm³) and low H-bond forming capability (E_H-bond = 0 kcal/mol) restricted terbinafine (low permeation-high retention) in terms of partitioning (k_D-SC = 0.09). Diclofenac (low permeation-low retention) stabilized skin lipids through the formation of strong H-bonds and exhibited excessive drug-lipid miscibility (ΔH_{diclofenac-skin} = -128.73 J/g), thus restricting its skin absorption. This classification system reflects the most essential drug skin absorption characteristics and provides a theoretical basis for the design of transdermal/topical formulations.

Topical delivery of gambogic acid assisted by the combination of low-frequency ultrasound and chemical enhancers for chemotherapy of cutaneous melanoma

Anti-cutaneous melanoma activity of the skin-delivered gambogic acid (GA) has been reported in our previous study. However, it is difficult for GA to diffuse passively through intact skin without any enhancement means. In this study, a combination of chemical enhancers (EN: azone and propylene glycol) and physical ultrasound (US) was used to improve the percutaneous permeation of GA and enhance the anti-melanoma activity. The enhancement effect of the combination of EN and US (EN-US) on GA in vitro and in vivo was studied, and the enhancement mechanism and skin irritation were also evaluated. We showed that the parameters of US application at a constant frequency (30 kHz) with a duty cycle of 100% and intensity of 1.75 W/cm² for 20 min were optimal. In vitro, EN-US showed a considerable enhancement of the permeation of GA, and the enhancement effect was stronger than that with the use of EN or US alone. In vivo antitumor study showed that the tumor growth was significantly inhibited after percutaneous administration of GA by EN-US, more than in the intravenous injection group. The penetration enhancement mechanism revealed that EN-US not only altered the structure of lipid bilayers and keratins to reduce the barrier effect of the stratum corneum but also produced diffusion channels in the skin under the cavitation effect of US, thereby promoting the skin penetration of GA. In addition, there was no observable skin irritation in mice after treatment with EN-US. Our study demonstrated that the combination of EN and US improved the skin permeation and retention of GA to enhance the anti-melanoma activity. This method also provides technical guidance for the future development of topical and transdermal therapeutic system of GA.

An investigation on the effect of drug physicochemical properties on the enhancement strength of enhancer: The role of drug-skin-enhancer interactions

The aim of present work was to investigate the influence of drug physicochemical properties on the enhancement effect of enhancers, which guided the application of enhancers in different drug transdermal prescriptions. Firstly, Polyglyceryl-3 dioleate (POCC) was selected as a model enhancer and its enhancement effect on ten drugs was assessed by in vitro skin permeation experiment. Secondly, the correlation analysis of physicochemical properties of drugs was carried out from the aspects of partition and permeation. The interactions of drug-skin-POCC were elucidated by FT-IR, molecular docking, solubility parameters calculation, ATR-FTIR, Raman study, molecular dynamics simulation and confocal laser scanning microscopy (CLSM). The results showed that the enhancement ratio (ER) of drugs was ranging from 2.23 to 7.45. On one hand, the miscibility between drugs with low polar surface area (P.S.A) and donor solution was decreased more pronounced by the addition of POCC because of the drug was difficult to form hydrogen-bond with POCC, facilitating the vehicle/SC partition of drugs. On the other hand, the permeation of drugs with low P.S.A and polarizability was enhanced more significantly by POCC because the drug was less likely to interact with skin lipids compared to others, causing that POCC had more chance to interact with skin lipids to improve permeation drugs across the SC more easily. In conclusion, the different strength of drug-skin-POCC interactions was the main reason for the discrepancy in the enhancement effect of the POCC on ten drugs, which laid a basis for the research on the drug-specific molecular mechanisms of enhancers.

Effect of Chemical Penetration Enhancer-Adhesive Interaction on Drug Release from Transdermal Patch: Mechanism Study Based on FT-IR Spectroscopy, 13C NMR Spectroscopy, and Molecular Simulation

Chemical penetration enhancers (CPEs) are commonly added into transdermal patches to impart improved skin permeation of drug. However, significant unexplained variability in drug release kinetics in transdermal patches is possible as a result of the addition of CPEs; investigations into the underlying mechanisms are still limited. In the present study, a diverse set of CPEs was employed to draw broad conclusions. Solubility parameters of CPEs and acrylate pressure-sensitive adhesive were calculated by molecular dynamics simulation and Fedors group contribution method to evaluate drug-adhesive miscibility. CPE-adhesive interaction was characterized by FT-IR study, ¹³C NMR spectroscopy, and molecular docking simulation. Results showed that release enhancement ratio (ER_R) of CPEs for zolmitriptan was rank ordered as isopropyl myristate > azone > Plurol Oleique^® CC497 > Span^® 80 > N-methylpyrrolidone > Transcutol^® P. It was found that solubility parameter difference (Δδ) between CPE and adhesive was negatively related with ER_R. It was proved that hydrogen bonding between CPE and adhesive would increase drug release rate, but only if the CPE showed good miscibility with adhesive. CPE like isopropyl myristate, which had good miscibility with adhesive, could decrease drug-adhesive interaction leading to the release of drug from adhesive.

Chiral 4-O-acylterpineol as transdermal permeation enhancers: insights of the enhancement mechanisms of a transdermal enantioselective delivery system for flurbiprofen

In order to devise more effective penetration enhancers, 4-O-acylterpineol derivatives which were expected to be hydrolyzed into nontoxic metabolites by esterase in the living epidermis, were synthesized from 4-terpineol (4-TER) enantiomers and straight chain fatty acids. Their promoting activities on the SR-flurbiprofen and its enantiomers were tested across full-thickness rabbit skin, as well as to correlate under in vitro and in vivo conditions. The permeation studies indicated that both d-4-O-acylterpineol and l-4-O-acylterpineol had significant enhancing effects, interestingly, d-4-O-aclyterpineol had higher enhancing effects than l-4-O-aclyterpineol with the exception of d-4-methyl-1-(1-methylethyl)-3-cyclohexen-1-yl octadec-9-enoate (d-4-T-dC18). The mechanism of 4-O-acylterpineol facilitating the drug penetration across the skin was confirmed by Attenuated total reflection-Fourier transformed infrared spectroscopy (ATR-FTIR) and molecular simulation. The mechanism of penetration enhancers promoting drug release was explored by the in vitro release experiment. Finally, a relative safety skin irritation of enhancers was also investigated by in vivo histological evaluation. The present research suggested that d-4-O-aclyterpineol and l-4-O-aclyterpineol could significantly promote the penetration of SR-flurbiprofen and its enantiomers both in vitro and in vivo, with the superiorities of high flux and low dermal toxicity.

Development and Evaluation of Cucurbitacin B Microemulsion: the Effect of Oil Phase and Aqueous Phase on Drug Percutaneous Absorption Based on ATR-FTIR Spectroscopy and Molecular Modeling

The present study aimed to develop a cucurbitacin B microemulsion (CuB-ME) and investigate the mechanism of the enhanced drug skin absorption at the molecular level. Firstly, the pseudo-ternary phase diagrams were developed to evaluate the effect of composition on microemulsion properties systematically. The formulation composition types and ratios of oil phase, surfactant, co-surfactant, and aqueous phase were optimized by an in vitro skin permeation experiment, and the optimized formula was confirmed with the pharmacodynamics study. Furthermore, the molecular mechanism of enhanced skin permeation was investigated using ATR-FTIR and molecular modeling. As a result, the optimized CuB-ME formulation was composed of Azone:Tween 80:ethanol:water = 2.5:16.9:5.6:75.0 (w/w/w/w). The oil phase improved skin permeation by disordering the stratum corneum intercellular liquid, while the aqueous phase impacted the particle size of the microemulsion and permeability coefficient of the drug. Besides, the hydration state of skin lipid also enhanced drug permeation by the interaction of water and the polar head of ceramide. The in vitro skin permeation amount was 45.47 ± 10.39 μg/cm², and no significant skin irritation was observed. The pharmacodynamics study demonstrated that CuB-ME had a significant therapeutic effect on the animal tumor model. In conclusion, the CuB-ME was developed successfully and the effect of the oil phase and aqueous phase on drug skin permeation was clarified at the molecular level.

Delivery of benzoylaconitine using biodegradable nanoparticles to suppress inflammation via regulating NF-κB signaling

Rheumatoid arthritis (RA) is a kind of systemic autoimmune disease, and patients with RA usually suffer serious pain, resulting in low quality of life. The development of drug delivery systems (DDSs) provides a valid approach for RA therapy via inhibiting the secretion of inflammatory cytokines from macrophages. As a prevailing drug nanocarrier with distinctive superiority, polymeric nanoparticles (NPs) have attracted much attention in recent years. However, low biocompatibility and limited exploitation of drug with high efficiency are still the main challenges in RA treatment. To overcome the limitations, we prepared a biocompatible copolymer methoxy-poly(ethylene glycol)-poly(lactide-co-glycolide) (mPEG-PLGA). Moreover, benzoylaconitine (BAC) with superior anti-inflammatory effect was selected as model drug. It was isolated from Aconitum kusnezoffii Reichb and encapsulated into mPEG-PLGA NPs (NP/BAC) to increase the bioavailablity of BAC. The NPs exhibited high cytocompatibility for activated macrophages and well compatibility with red blood cells. Furthermore, the anti-inflammatory property of NP/BAC was testified by substantially inhibiting secretion of pro-inflammatory cytokines. The TNF-α and IL-1β cytokines of NP/BAC group reduced 70 % and 66 % compared with that of activated macrophages. Especially, NP/BAC reduced the overexpression of NF-κB p65 to inhibit NF-κB signaling pathway, which was a critical regulator of inflammatory responses. NP/BAC also showed efficient in vivo anti-inflammatory effect with high ear (69.8 %) and paw (87.1 %) swelling suppressing rate. These results revealed the anti-inflammatory mechanism of NP/BAC and proved it was a suitable DDS to suppress inflammation, providing a promising strategy for RA therapy and research of Aconitum kusnezoffii Reichb.