Transdermal and dermal delivery of adefovir: Effects of pH and permeation enhancers

Systematic establishment of the relationship between skin absorption and toxicity of furanoids via in silico, in vitro, and in vivo assessments

Furanoids are a class of contaminants prevalent in both airborne and occupational environments, with potential health implications through inhalation, oral ingestion, and skin penetration. Given their diminutive molecular size, there is a presumption that furanoids can readily permeate the skin. To systematically explore this presumption, we investigated the skin absorption and toxicity of a series of furans (furfuryl alcohol, furfuryl acetate, furfural, methyl 2-furoate, and 5-methylfurfural) using in silico, in vitro, and in vivo models. The in vitro permeation test (IVPT) from neat and aqueous suspension (5 mM) of furans demonstrated a facile absorption through pig and nude mouse skins. The lipophilicity of furans significantly influenced skin deposition, with higher lipophilicity displaying greater deposition. However, an opposing trend emerged in the receptor compartment accumulation. In barrier-defective skin simulating atopic dermatitis (AD) and psoriasis, enhanced deposition occurred with more hydrophilic furans but not with the more lipophilic ones. In the cell-based study, furanoids induced the proliferation of keratinocytes and skin fibroblasts except for the compounds with the aldehyde group (furfural and 5-methylfurfural). Both furfuryl acetate and 5-methylfurfural activated keratinocytes via the overexpression of COX-2 and PGE2 by 1.5‒2-fold. This stimulation involved the mitogen-activated protein kinase (MAPK) signaling pathway. For the in vivo mouse skin treatment, we selected furfuryl acetate (hydrophilic) and 5-methylfurfural (lipophilic). Both furans showed different patterns of skin lesions, where repeated application of furfuryl acetate caused epidermal hyperplasia and scaling, while 5-methylfurfural predominantly evoked skin inflammation and barrier disintegration. Toxicokinetics analysis revealed a higher plasma concentration of topically applied furfuryl acetate than that of the 5-methylfurfural (5.04 versus 2.34 nmol/ml), resulting in the mild injury of furfuryl acetate-treated peripheral organs. Conversely, no notable adverse effects on organs were observed for the 5-methylfurfural. This study established the relationship between cutaneous absorption and the toxicity of furans following skin exposure.

Design Principles and Applications of Ionic Liquids for Transdermal Drug Delivery

Ionic liquids (ILs) are salts with melting points typically <100 °C, composed of specific anions and cations. Recently, IL application has expanded into material engineering and biomedicine. Due to their unique properties, ILs have garnered significant interest in pharmacological research as solubilizers, transdermal absorption enhancers, antibacterial agents, and stabilizers of insoluble pharmaceutical active ingredients. The improvement of skin permeability by ILs is closely associated with their specific physicochemical characteristics, which are identified by their ionic composition. However, the existing literature on transdermal medication administration is insufficient in terms of a comprehensive knowledge base. This review provides a comprehensive assessment of the design principles involved in IL synthesis. Additionally, it discusses the methods utilized to assess skin permeability and provides a focused outline of IL application in transdermal drug administration.

Impact of Formulation and Microneedle Length on Transdermal Metronidazole Permeation through Microneedle-Treated Skin

OBJECTIVE

This study aimed to determine the impact of formulation (gel vs cream) and microneedle characteristics (length, number) on permeation of metronidazole through excised microneedle-treated skin. The long-term goal is to apply these results towards a pharmacokinetic study in human subjects with diverse skin types, using in vitro flux data to determine dosing conditions and ultimately establish in vitro-in vivo correlations.

METHODS

Metronidazole release from 0.75% gel and cream was quantified with flow-through diffusion cells, using a cellulose membrane. Excised porcine skin was treated with stainless steel microneedles (500 or 800 μm length), to create 50 or 100 micropores. Metronidazole gel or cream was applied to microneedle-treated skin and replaced every 48 h for up to 7 days. Metronidazole permeation was quantified using HPLC. Intact skin (no microneedle treatment) served as controls.

RESULTS

Metronidazole release was faster from the gel vs cream. At 7 days there was no difference between gel vs cream in total metronidazole permeated through intact skin. For both formulations, metronidazole permeation was significantly higher (vs intact skin) following microneedle application, regardless of microneedle length or micropore number. Increasing microneedle length and micropore number enhanced MTZ permeation multiple fold for both gel and cream. The greatest enhancement in total permeation for both formulations was achieved with the 800 μm MN, 100 micropore condition.

CONCLUSIONS

Formulation and microneedle conditions both impacted metronidazole permeation. These data will be used to estimate in vivo serum concentrations after applying metronidazole to microneedle-treated skin in humans.

Film-Forming Sprays for Topical Drug Delivery

Film-forming sprays offer many advantages compared to conventional topical preparations because they can provide uniform drug distribution and dose, increased bioavailability, lower incidence of irritation, continuous drug release, and accelerated wound healing through moisture control. Film-forming sprays consist of polymers and excipients that improve the characteristics of preparations and enhance the stability of active substances. Each type of polymer and excipient will produce films with different features. Therefore, the various types of polymers and excipients and their evaluation standards need to be examined for the development of a more optimal form of film-forming spray. The selected literature included research on polymers as film-forming matrices and the application of these sprays for medical purposes or for potential medical use. This article discusses the types and concentrations of polymers and excipients, sprayer types, evaluations, and critical parameters in determining the sprayability and film characteristics. The review concludes that both natural and synthetic polymers that have in situ film or viscoelastic properties can be used to optimise topical drug delivery.

Stratum corneum modulation by chemical enhancers and lipid nanostructures: implications for transdermal drug delivery

Skin is the outermost and largest protective covering of the body. The uppermost layer of the skin, stratum corneum also called the horny layer is composed of keratin-filled cells covered by a lipid matrix which shields the skin from physical and chemical entrants. The lipid lamellar structure comprises of ceramides, cholesterol, fatty acids and proteins. Chemical enhancers that mimic the lamellar chemistry, reversibly fluidize the latter can be utilized for enhancing transport of cargo across the epidermis into the dermis. This review deals with the stratum corneum chemistry, mechanisms to modulate its packing with the aid of chemical enhancers, biophysical techniques for characterization and applications in the design of nature-inspired biocompatible lipid nanostructures for transdermal delivery of drugs and bioactive agents.

Galactosyl Pentadecene Reversibly Enhances Transdermal and Topical Drug Delivery

PURPOSE

To study new skin penetration/permeation enhancers based on amphiphilic galactose derivatives.

METHODS

Two series of alkyl and alkenyl galactosides were synthesized and evaluated for their enhancing effect on transdermal/topical delivery of theophylline (TH), hydrocortisone (HC) and cidofovir (CDV), reversibility of their effects on transepidermal water loss (TEWL) and skin impedance, interaction with the stratum corneum using infrared spectroscopy, and cytotoxicity on keratinocytes and fibroblasts.

RESULTS

Initial evaluation identified 1-(α-D-galactopyranosyl)-(2E)-pentadec-2-ene A15 as a highly potent enhancer - it increased TH and HC flux through human skin 8.5 and 5 times, respectively. Compound A15 increased the epidermal concentration of a potent antiviral CDV 7 times over that reached by control and Span 20 (an established sugar-based enhancer). Infrared spectroscopy of human stratum corneum indicated interaction of A15 with skin barrier lipids but not proteins. These effects of A15 on the skin barrier were reversible (both TEWL and skin impedance returned to baseline values within 24 h after A15 had been removed from skin). In vitro toxicity of A15 on HaCaT keratinocytes and 3T3 fibroblasts was acceptable, with IC₅₀ values over 60 μM.

CONCLUSIONS

Galactosyl pentadecene A15 is a potent enhancer with low toxicity and reversible action.

Transdermal nitroglycerin delivery using acrylic matrices: design, formulation, and in vitro characterization

Nitroglycerin (TNG) transdermal drug delivery systems (TDDSs) with different acrylic pressure-sensitive adhesives (PSAs) and chemical permeation enhancers (CPEs) were prepared. The effects of PSAs and CPEs types and concentrations on skin permeation and in vitro drug release from devices were evaluated using the dissolution method as well as the modified-jacketed Franz diffusion cells fitted with excised rat abdominal skin. It was demonstrated that the permeation rate or steady state flux (J_ss) of the drug through the excised rat skin was dependent on the viscosity and type of acrylic PSA as well as the type of CPE. Among different acrylic PSAs, Duro-Tak 2516 and Duro-Tak 2054 showed the highest and Duro-Tak 2051 showed the lowest J_ss. Among the various CPEs, propylene glycol and cetyl alcohol showed the highest and the lowest enhancement of the skin permeation of TNG, respectively. The adhesion properties of devices such as 180° peel strength and probe tack values were obtained. It was shown that increasing the concentration of CPE led to reduction in the adhesion property of PSA. Moreover, after optimization of the formulation, it was found that the use of 10% PG as a CPE and 25% nitroglycerin loading in Duro-Tak 2054 is an effective monolithic DIAP for the development of a transdermal therapeutic system for nitroglycerin.

Maximizing dermal targeting and minimizing transdermal penetration by magnolol/honokiol methoxylation

Magnolol and honokiol, predominant active compounds in the family Magnoliaceae, are known to exhibit strong anti-inflammatory activities against dermal disorders. We attempted to modify the structures of magnolol and honokiol by methoxylation to optimize the skin delivery ability. Absorption of these permeants into and through the skin was performed at both an infinite dose and saturated solubility. Superoxide anion and elastase released from human neutrophils were the biomarkers used to examine anti-inflammatory potencies of these permeants. The safety of the permeants was evaluated by keratinocyte viability and in vivo bioengineering techniques. Topical magnolol and honokiol at an infinite dose (7.5 mM) showed skin accumulations of 0.22 and 0.16 nmol/mg, respectively. Methoxylation significantly enhanced their skin absorption. Deposition amounts of dimethylmagnolol and dimethylhonokiol were respectively 15- and 7-fold greater than those of magnolol and honokiol. Contrary to the skin accumulation results, the transdermal penetration across skin decreased following methoxylation. No transdermal delivery occurred for dimethylhonokiol. Skin uptake of 4'-O-methylhonokiol was 2-fold higher than that of 2-O-methylhonokiol, although they are isomers. Methoxylated permeants demonstrated selective absorption into follicles, which showed 3-5-fold higher follicular amounts compared to magnolol and honokiol. The relative order of anti-inflammatory activities was honokiol>2-O-methylmagnolol>dimethylhonokiol>magnolol. The other compounds exhibited negligible or negative responses in activated neutrophils. Magnolol and honokiol induced slight but significant keratinocyte cytotoxicity and stratum corneum disruption. Daily administration of methoxylated permeants, especially dimethylhonokiol, produced no skin irritation for up to 7 days. Methoxylated magnolol and honokiol can be efficient and safe candidates for treating inflammatory skin disorders.

In vitro and in vivo percutaneous absorption of seleno-L-methionine, an antioxidant agent, and other selenium species

AIM

To investigate the in vitro and in vivo percutaneous absorption of seleno-L-methionine (Se-L-M), an ultraviolet (UV)-protecting agent, from aqueous solutions.

METHODS

Aqueous solutions of Se-L-M were prepared in pH 4, 8, and 10.8 buffers. The pH 8 buffer contained 30% glycerol, propylene glycol (PG) and polyethylene glycol (PEG) 400. The in vitro skin permeation of Se-L-M via porcine skin and nude mouse skin was measured and compared using Franz diffusion cells. The in vivo skin tolerance study was performed, which examined transepidermal water loss (TEWL), skin pH and erythema.

RESULTS

In the excised porcine skin, the flux was 0.1, 11.4 and 8.2 μg·cm(-2)·h(-1) for the pH 4, 8, and 10.8 buffers, respectively. A linear correlation between the flux and skin deposition was determined. According to permeation across skin with different treatments (stripping, delipidation, and ethanol treatments), it was determined that the intracellular route comprised the predominant pathway for Se-L-M permeation from pH 8 buffer. Aqueous solutions of seleno-DL-methionine (Se-DL-M), selenium sulfide and selenium-containing quantum dot nanoparticles were also used as donor systems. The DL form showed a lower flux (7.0 vs 11.4 μg·cm(-2)·h(-1)) and skin uptake (23.4 vs 47.3 μg/g) as compared to the L form, indicating stereoselective permeation of this compound. There was no or only negligible permeation of selenium sulfide and quantum dots into and across the skin. With in vivo topical application for 4 and 8 h, the skin deposition of Se-L-M was about 7 μg/g, and values were comparable to each other. The topical application of Se-L-M for up to 5 d did not caused apparent skin irritation. However, slight inflammation of the dermis was noted according to the histopathological examination.

CONCLUSION

Se-L-M was readily absorbed by the skin in both the in vitro and in vivo experiments. The established profiles of Se-L-M skin absorption will be helpful in developing topical products of this compound.

A biomimetic chitosan derivates: preparation, characterization and transdermal enhancement studies of N-arginine chitosan

A novel arginine-rich chitosan (CS) derivates mimicked cell penetration peptides; N-Arginine chitosan (N-Arg-CS) was prepared by two reaction methods involving activated L-arginine and the amine group on the chitosan. FTIR spectra showed that arginine was chemically coupled with CS. Elemental analysis estimated that the degrees of substitution (DS) of arginine in CS were 6%, 31.3% and 61.5%, respectively. The drug adefovir was chosen as model and its permeation flux across excised mice skin was investigated using a Franz diffusion cell. The results showed that the most effective enhancer was 2% (w/v) concentration of 10 kDa N-Arg-CS with 6% DS. At neutral pH, the cumulative amount of adefovir permeated after 12 hours was 2.63 ± 0.19 mg cm⁻² which was 5.83-fold more than adefovir aqueous solution. Meanwhile N-Arg-CS was 1.83, 2.22, and 2.45 times more effective than Azone, eucalyptus and peppermint, respectively. The obtained results suggest that N-Arg-CS could be a promising transdermal enhancer.

Enhanced dissolution and stability of adefovir dipivoxil by cocrystal formation

OBJECTIVES

The objectives of this study were to prepare and characterize the novel adefovir dipivoxil-saccharin cocrystal and to demonstrate the enhanced dissolution and stability of adefovir dipivoxil by cocrystal formation.

METHODS

Adefovir dipivoxil-saccharin cocrystal was prepared using a novel solution crystallization approach and scaled up to 30 g for subsequent studies. DSC, IR and XRPD were used to characterize the novel solid form. The stoichiometry of the cocrystal was analysed by HPLC. Dissolution and chemical stability were assessed and compared with marketed adefovir dipivoxil (form 1) used in marketed Hepsera Tablets.

KEY FINDINGS

A new solid adefovir dipivoxil-saccharin cocrystal with unique melting point, DSC, FTIR and XRPD data was obtained. The molar ratio of adefovir dipivoxil and saccharin in the cocrystal was determined to be 1 : 1. The cocrystal had a pH-independent dissolution profile and showed a two-fold increase in the dissolution efficiency in water and phosphate buffer (pH 6.8) compared with adefovir dipivoxil. The cocrystal was kinetically much more stable than form 1. Form 1 degraded almost completely at 60°C in 18 days, while adefovir dipivoxil-saccharin cocrystal remained unchanged for 47 days at 60°C.

CONCLUSIONS

This study demonstrated that the dissolution and stability of adefovir dipivoxil could be significantly enhanced by its cocrystal formation with saccharin. The use of cocrystals could be a feasible and valuable approach for improving the physicochemical properties of adefovir dipivoxil.

Effect of O-acylmenthol and salt formation on the skin permeation of diclofenac acid

PURPOSE

To enhance the transdermal delivery of diclofenac acid (DA) by using O-acylmenthol as a penetration enhancer and complexing with amines, or by a combination of the two methods.

METHODS

The skin permeability of diclofenac was tested in vitro across rat skin with each of the evaluated permeants in a saturated isopropyl myristate (IPM) donor solution.

RESULTS

A 4.5-fold increase in the flux of diclofenac was observed by ion-pair formation with diethylamine; however, the cations with hydroxyl groups had negative effects on the transdermal delivery of diclofenac. 2-isopropyl-5-methylcyclohexyl 2-hydroxypanoate and 2-isopropyl-5-methylcyclohexyl heptanoate produced significant increase in the permeation of diclofenac potassium (D-K); however, both of them were ineffective for the other diclofenac salts, including diclofenac diethylamine (D-DETA), diclofenac ethanolamine (D-EA), diclofenac diethanolamine (D-DEA), diclofenac triethanolamine, and diclofenac N-(hydroxylethyl) piperidine. 2-isopropyl-5-methylcyclohexyl tetradecanoate was effective on the penetration of D-K, D-DETA, D-EA, and D-DEA. Also, it is exciting to note that the combined use of diethylamine with 2-isopropyl-5-methylcyclohexyl tetradecanoate produced a 9.74-fold increase in accumulation amount of diclofenac compared with DA in IPM.

CONCLUSIONS

The use of ion pair in combination with O-acylmenthol is necessary to further increase the diclofenac flux to provide better compliance for the patients undergoing clinical therapy.

Topical delivery of silymarin constituents via the skin route

AIM

Silibinin (SB), silydianin (SD), and silychristin (SC) are components of silymarin. These compounds can be used to protect the skin from oxidative stress induced by ultraviolet (UV) irradiation and treat it. To this end, the absorption of silymarin constituents via the skin was examined in the present report.

METHODS

Transport of SB, SD, and SC under the same thermodynamic activity through and into the skin and the effects of pH were studied in vitro using a Franz diffusion assembly.

RESULTS

The lipophilicity increased in the order of SC<SD<SB. Increased lipophilicity of a compound resulted in higher skin deposition but had a minor effect on permeation across the skin in the less-ionized form (pH 8). It is apparent that compounds in the less-ionized form showed higher skin uptake compared to the more-ionized form. Hyperproliferative skin produced by UVB exposure showed increased permeation of silymarin constituents in the less-ionized form, but it did not affect deposition within the skin. With in vivo topical application for 4 and 8 h, the skin deposition of SB was higher than those of SD and SC by 3.5 approximately 4.0- and 30 approximately 40-fold, respectively. The skin disruption and erythema test demonstrated that the topical application of these compounds for up to 24 h caused no apparent skin irritation.

CONCLUSION

The basic profiles of silymarin permeation via skin route were established.

Transdermal delivery of carvedilol in rats: probing the percutaneous permeation enhancement mechanism of soybean extract-chitosan mixture

BACKGROUND

This study was designed for investigating the effect of soybean (SS) extract and chitosan (CTN) in facilitating the permeation of carvedilol (CDL) across rat epidermis.

METHOD

Transdermal flux of carvedilol through heat-separated rat epidermis was investigated in vitro using vertical Keshary-Chien diffusion cells. Biophysical and microscopic manifestations of epidermis treated with SS-extract, CTN, and SS extract-CTN mixture were investigated by using DSC, TEWL, SEM, and TEM. Biochemical estimations of cholesterol, sphingosine, and triglycerides were carried out for treated excised as well as viable rat epidermis. The antihypertensive activity of the patches in comparison to that after oral administration of carvedilol was studied in deoxycorticosterone acetate-induced hypertensive rats.

RESULTS

The solubility of CDL was found to be maximum in the presence of 1% (w/v) SS extract. The K(IPM/PB) of CDL decreased with increase in concentration of SS extract. The in vitro permeation of CDL across rat epidermis increased and was maximum with combination of SS extract and chitosan (CTN). Biochemical and microscopic studies revealed the initiation of reversal of barrier integrity after 12 hours. Furthermore, the application of patches containing SS extract-CTN mixture resulted in sustained release of carvedilol, which was able to control the hypertension in deoxycorticosterone acetate (DOCA) induced hypertensive rats through 24 hours. CTN was found to potentiate the permeation enhancing activity of SS extract.

CONCLUSION

The developed transdermal patches of CDL containing SS extract-CTN mixture exhibited better performance as compared to oral administration in controlling hypertension in rats.