Quantitative structure-permeation relationship for iontophoretic transport across the skin

Iontophoresis on Porcine and Human Gingiva

PURPOSE

Iontophoresis is a noninvasive method that enhances drug delivery using an electric field. This method can improve drug delivery to the tissues in the oral cavity. The effects of iontophoresis on gingival drug delivery have not been investigated. The objectives of this study were to (a) determine the flux enhancement of model permeants across porcine and human gingiva during iontophoresis, (b) examine the transport mechanisms of gingival iontophoresis, and (c) evaluate the potential of iontophoretically enhanced delivery for three model drugs lidocaine, ketorolac, and chlorhexidine.

METHODS

Passive and iontophoretic fluxes were determined with porcine and human gingiva using a modified Franz diffusion cell and model drugs and permeants. To investigate the transport mechanisms of iontophoresis, the enhancement from the direct-field effect was determined by positively and negatively charged model permeants. The electroosmosis enhancement effect was determined with neutral permeants of different molecular weight. The alteration of the gingival barrier due to electropermeabilization was evaluated using electrical resistance measurements.

RESULTS

Significant flux enhancement was observed during gingival iontophoresis. The direct-field effect was the major mechanism governing the iontophoretic transport of the charged permeants. Electroosmosis was from anode to cathode. The effective pore radius of the iontophoretic transport pathways in the porcine gingiva was ~0.68 nm. Irreversible electropermeabilization was observed after 2 and 4 h of iontophoresis under the conditions studied.

CONCLUSION

Iontophoresis could enhance drug delivery and reduce transport lag time, showing promise for gingival drug delivery.

Anti-inflammatory ethosomal nanoformulation in combination with iontophoresis in chronic wound healing: An ex vivo study

Prescription of anti-inflammatory drugs may be considered as a promising strategy in chronic wound healing where the inflammatory disturbance has delayed the healing process. It seems that hydrocortisone 17-butyrate (HB17) would be promising in the form of a nano-formulation to enhance drug delivery efficacy. In the present study, transdermal delivery of nano-HB17 in combination with iontophoresis was investigated ex vivo. Ethosomal-HB17 was synthesised using lecithin, ethanol and cholesterol with a different ratio by hot method. The negative ethosomal-HB17 particle size was around 244 ± 4.3 nm with high stability of up to 30 days. Additionally, evaluated entrapment efficiency of HB17 in ethosomes by high performance liquid chromatography was 40.6 ± 2.21%. Moreover, the permeation speed and amount of H17B in complete-thickness rat skin in the presence and absence of iontophoresis showed that the penetration of free H17B and ethosomal-H17B formulations were zero and 7.98 μg/cm² in 120 min, respectively. Whereas in the case of applying iontophoresis, permeation amount obtained was zero and 19.69 μg/cm² in 30 min in free H17B and ethosomal-H17B formulations, respectively. It has been concluded that transdermal delivery of ethosomal-H17B is an effective strategy to enhance drug delivery and it will be improved when it is combined with iontophoresis.

Inorganic ions in the skin: Allies or enemies?

Skin constitutes a barrier protecting the organism against physical and chemical factors. Therefore, it is constantly exposed to the xenobiotics, including inorganic ions that are ubiquitous in the environment. Some of them play important roles in homeostasis and regulatory functions of the body, also in the skin, while others can be considered dangerous. Many authors have shown that inorganic ions could penetrate inside the skin and possibly induce local effects. In this review, we give an account of the current knowledge on the effects of skin exposure to inorganic ions. Beneficial effects on skin conditions related to the use of thermal spring waters are discussed together with the application of aluminium in underarm hygiene products and silver salts in treatment of difficult wounds. Finally, the potential consequences of dermal exposure to topical sensitizers and harmful heavy ions including radionuclides are discussed.

Influence of Chemical Enhancers and Iontophoresis on the In Vitro Transdermal Permeation of Propranolol: Evaluation by Dermatopharmacokinetics

The aims of this study were to assess, in vitro, the possibility of administering propranolol transdermally and to evaluate the usefulness of the dermatopharmacokinetic (DPK) method in assessing the transport of drugs through stratum corneum, using propranolol as a model compound. Four chemical enhancers (decenoic and oleic acid, laurocapram, and R-(+)-limonene) and iontophoresis at two current densities, 0.25 and 0.5 mA/cm² were tested. R-(+)-limonene, and iontophoresis at 0.5 mA/cm² were proven to be the most efficient in increasing propranolol transdermal flux, both doubled the original propranolol transdermal flux. Iontophoresis was demonstrated to be superior than the chemical enhancer because it allowed faster delivery of the drug. The DPK method was sufficiently sensitive to detect subtle vehicle-induced effects on the skin permeation of propranolol. The shorter duration of these experiments and their ability to provide mechanistic information about partition between vehicle and skin and diffusivity through skin place them as practical and potentially insightful approach to quantify and, ultimately, optimize topical bioavailability.

Iontophoretic Drug Delivery in the Oral Cavity

Iontophoresis is a noninvasive method to enhance systemic and local drug delivery by the application of an electric field. For systemic drug delivery in the oral cavity, iontophoresis was studied primarily for transbuccal delivery. Significant enhancement of drug delivery was observed in buccal iontophoresis compared to passive transport for different drugs. For local drug delivery in the oral cavity, iontophoresis could enhance drug penetration into the enamel, dentin, and other oral tissues for the treatment of oral diseases. Iontophoresis was evaluated in dentistry such as to produce local anesthesia and treat tooth decalcification and hypersensitivity, but this technology has not been fully utilized. The most common drugs in these evaluations were fluoride and lidocaine. In general, there is limited knowledge of the mechanisms of iontophoresis in the oral tissues. In vivo animal and human studies have suggested that iontophoresis is safe in the oral cavity under the conditions investigated. The present review covers the topics of iontophoretic drug delivery in the oral cavity for both systemic and local treatments. The anatomy and diseases in the oral cavity for iontophoretic drug delivery are also briefly reviewed, and the challenges for this drug delivery method are discussed.

Prolonged and localized sweat stimulation by iontophoretic delivery of the slowly-metabolized cholinergic agent carbachol

BACKGROUND

Continuous non-invasive sampling and sensing of multiple classes of analytes could revolutionize medical diagnostics and wearable technologies, but also remains highly elusive because of the many confounding factors for candidate biofluids such as interstitial fluid, tears, saliva, and sweat. Eccrine sweat biosensing has seen a recent surge in demonstrations of wearable sampling and sensing devices. However, for subjects at rest, access to eccrine sweat is highly limited and unpredictable compared to saliva and tears.

OBJECTIVE

Reported here is a prolonged and localized sweat stimulation by iontophoretic delivery of the slowly-metabolized nicotinic cholinergic agonist carbachol.

METHODS

Presented here are detailed measurements of natural baseline sweat rates across multiple days, confirming a clear need for localized sweat stimulation. Iontophoresis was performed with either carbachol or pilocarpine in order to stimulate sweat in subjects at rest. Furthermore, improved methods of quantifying sweat generation rates (nL/min/gland) are demonstrated.

RESULTS

In-vivo testing reveals that carbachol stimulation can surpass a major goal of 24-h sweat access, in some cases providing more than an order of magnitude longer duration than stimulation with commonly-used pilocarpine. Also demonstrated is reduction of the traditional iontophoretic dosage for sweat stimulation (<5.25-42mC/cm²). This increases the viability of repeated dosing as demonstrated herein, and for carbachol is as much as 100-1000X less than used for other applications.

CONCLUSION

This work is not only significant for wearable sweat biosensing technology, but could also have broader impact for those studying topical skin products, antiperspirants, textiles and medical adhesives, nerve disorders, the effects of perspiration on skin-health, skin related diseases such as idiopathic pure sudomotor failure and hyperhidrosis, and other skin- and perspiration-related applications.

Transdermal delivery of estradiol-loaded PLGA nanoparticles using iontophoresis for treatment of osteoporosis

BACKGROUND

Estradiol is one of the therapeutic agents for osteoporosis. We have reported transdermal permeability of estradiol-loaded nanoparticles, and permeability effect of estradiol was enhanced by using nanoparticle system and iontophoresis [Colloids and Surfaces B: Biointerfaces97 (2012), 84-89].

OBJECTIVE

This study was conducted in vivo to evaluate therapeutic efficacy of the estradiol-loaded PLGA nanoparticles for osteoporosis.

METHODS

Prior to the in vivo study, we have determined the surface charge density of the particles and found they have negatively charged polyelectrolyte layers on the surfaces. Ovariectomized female Sprague-Dawley rats were used as an animal model of osteoporosis. They were separated into three groups by administration route of estradiol-loaded PLGA nanoparticles, passive diffusion group, iontophoresis group and control. After treatment, we have measured bone mineral density of spine using an X-ray computed tomography system.

RESULTS

Bone mineral density after iontophoresis was significantly higher than that of passive diffusion and control group. By usage of iontophoresis, the nanoparticles were permeated through follicles and migrated into capillary vessel around follicles, and the loaded drug reached effective blood concentration in plasma of rat.

CONCLUSIONS

From this study, we found that the combination with charged nanoparticle system and iontophoresis is useful to osteoporosis treatment.

Evaluation of Drug Concentrations Delivered by Microiontophoresis

Microiontophoresis uses an electric current to eject a drug solution from a glass capillary and is often utilized for targeted delivery in neurochemical investigations. The amount of drug ejected, and its effective concentration at the tip, has historically been difficult to determine, which has precluded its use in quantitative studies. To address this, a method called controlled iontophoresis was developed which employs a carbon-fiber microelectrode incorporated into a multibarreled iontophoretic probe to detect the ejection of electroactive species. Here, we evaluate the accuracy of this method. To do this, we eject different concentrations of quinpirole, a D2 receptor agonist, into a brain slice containing the dorsal striatum, a brain region with a high density of dopamine terminals. Local electrical stimulation was used to evoke dopamine release, and inhibitory actions of quinpirole on this release were examined. The amount of drug ejected was estimated by detection of a coejected electrochemical marker. Dose response curves generated in this manner were compared to curves generated by conventional perfusion of quinpirole through the slice. We find several experimental conditions must be optimized for accurate results. First, selection of a marker with an identical charge was necessary to mimic the ejection of the cationic agonist. Next, evoked responses were more precise following longer periods between the end of the ejection and stimulation. Lastly, the accuracy of concentration evaluations was improved by longer ejections. Incorporation of these factors into existing protocols allows for greater certainty of concentrations delivered by controlled iontophoresis.

Ropinirole-dextran sulfate nanoplex for nasal administration against Parkinson's disease: in silico molecular modeling and in vitro-ex vivo evaluation

Dextran sulfate sodium (DS) was allowed to interact ionically with ropinirole hydrochloride (ROPI HCl, an anti-Parkinsonian agent) to synthesize self-assembled ROPI-DS nanoplex. The preliminary objective behind ROPI-DS complexation was to enhance the partitioning of ROPI HCl and thereby its encapsulation into nanocarriers and to improve the nasal membrane permeability. Molecular interactions were computed using in silico molecular modeling. Nanoplex were characterized for physicochemical and partitioning behavior. Optimized ROPI-DS nanoplex was further characterized by spectroscopic and thermal analysis, diffraction studies, morphological and histopathological analysis. In summary, ROPI-DS nanoplex represents a promising nanocarrier material for intranasal administration.

New nasal nanocomplex self-assembled from charged biomacromolecules: N,N,N-Trimethyl chitosan and dextran sulfate

Although chitosan (CHT, a linear cationic polysaccharide) is biodegradable, biocompatible, non-toxic, and mucoadhesive in nature, the low solubility of CHT in aqueous and alkaline media limits its applicability in pharmaceutical and biomedical field. This necessitate the introduction of new chemically-modified derivatives of CHT those can surmount the solubility barrier. Herein, N,N,N-trimethyl chitosan (TMC), a quaternized hydrophilic derivative of CHT, was synthesized by two-step reductive methylation of CHT and characterized for (1)H NMR and zeta potential measurements. Polyelectrolyte complexes (PECs) based on TMC and dextran sulfate (DS) were prepared via ionic interactions between charged functional groups of former polysaccharides at different pH conditions (pH 5, 8, 10, and 12) and characterized for physicochemical (particle size and zeta potential) and solid- state characterizations (HR-TEM, SEM, FTIR, TGA and XRD). At alkaline pH conditions, the participant polymer chains (TMC and DS) are sufficiently close to form more stable PECs. The release efficiency was assessed after loading a model drug into optimized PEC formulation. Data indicated that the PECs fabricated at alkaline pH presents a reliable formulation for pharmaceutical and biomedical applications.

Quantitative analysis of iontophoretic drug delivery from micropipettes

Microiontophoresis is a drug delivery method in which an electric current is used to eject molecular species from a micropipette. It has been primarily utilized for neurochemical investigations, but is limited due to difficulty controlling and determining the ejected quantity. Consequently the concentration of an ejected species and the extent of the affected region are relegated to various methods of approximation. To address this, we investigated the principles underlying ejection rates and examined the concentration distribution in microiontophoresis using a combination of electrochemical, chromatographic, and fluorescence-based approaches. This involved a principal focus on how the iontophoretic barrel solution affects ejection characteristics. The ion ejection rate displayed a direct correspondence to the ionic mole fraction, regardless of the ejection current polarity. In contrast, neutral molecules are ejected by electroosmotic flow (EOF) at a rate proportional to the barrel solution concentration. Furthermore, the presence of EOF was observed from barrels containing high ionic strength solutions. In practice, use of a retaining current draws extracellular ions into the barrel and will alter the barrel solution composition. Even in the absence of a retaining current, diffusional exchange at the barrel tip will occur. Thus behavior of successive ejections may slightly differ. To account for this, electrochemical or fluorescence markers can be incorporated into the barrel solution in order to compare ejection quantities. These may also be used to provide an estimate of the ejected amount and distribution provided accurate use of calibration procedures.

Controlled synthesis of N,N,N-trimethyl chitosan for modulated bioadhesion and nasal membrane permeability

In an experiment to explore the bioadhesion, biocompatibility, and membrane permeation properties, the controlled synthesis of N,N,N-trimethyl chitosan (TMC) was carried out by two-step reductive methylation of chitosan (CHT). Methylation was confirmed by (1)H NMR (δ=3.1 ppm) and FTIR analysis (CH stretch at 1,485 cm(-1)). The TMC was further characterized by DSC, TGA, XRD, HR-TEM, SEM, and elemental analysis. Findings revealed improved solubility, enhanced viscosity, increased swelling index and higher molecular weight of TMC over CHT. Comparative evaluation validated increased bioadhesion potential, and improved ex vivo biocompatibility of TMC compared to CHT. Increased bioadhesion of TMC NPs over CHT NPs can be attributed to the strong electrostatic interactions between cationic amino groups with anionic sialic and sulfonic acid moieties contained in the mucin of the nasal mucus. Ex vivo biocompatibility studies suggested that the NP formulations of both biopolymers were biocompatible and could be applied safely on the nasal epithelium. Ex vivo permeation studies executed on excised cattle nasal mucosa illustrated improved permeability of TMC NPs over CHT NPs. In the author's opinion, two-step reductive methylation of CHT could be an attractive strategy to improve its solubility, bioadhesion, and permeation characteristics without affecting biocompatibility across the mucosal surfaces.

Effective use of transdermal drug delivery in children

Transdermal administration offers a non-invasive and convenient method for paediatric drug delivery. The competent skin barrier function in term infants and older children limits both water loss and the percutaneous entry of chemicals including drugs; but the smaller doses required by children eases the attainment of therapeutic concentrations. Transdermal patches used in paediatrics include fentanyl, buprenorphine, clonidine, scopolamine, methylphenidate, oestrogens, nicotine and tulobuterol. Some patches have paediatric labelling supported by clinical trials whereas others are used unlicensed. Innovative drug delivery methods, such as microneedles and sonophoresis are being tested for their safety and efficacy; needleless injectors are primarily used to administer growth hormone; and two iontophoretic devices were approved for paediatrics. In contrast, the immature and rapidly evolving skin barrier function in premature neonates represents a significant formulation challenge. Unfortunately, this population group suffers from an absence of approved transdermal formulations, a shortcoming exacerbated by the significant risk of excessive drug exposure via the incompletely formed skin barrier.

Designing in-vitro systems to simulate the in-vivo permeability of drugs

In this work an engineering approach, consisting in an experimental procedure and a model to derive the data, was presented and applied to improve the testing methods of pharmaceuticals. The permeability of several active molecules have been evaluated across a synthetic membrane. The permeability of these drugs measured through the artificial membrane were successfully correlated to their in-vivo permeability. The relationship with in-vivo permeability was derived, and then a rule to design systems to simulate the intestinal absorption was proposed to reduce the need for expensive and ethical problematic in-vivo measurements.

Time-dependent expression of hypertonic effects on bullfrog taste nerve responses to salts and bitter substances

We previously showed that the hypertonicity of taste stimulating solutions modified tonic responses, the quasi-steady state component following the transient (phasic) component of each integrated taste nerve response. Here we show that the hypertonicity opens tight junctions surrounding taste receptor cells in a time-dependent manner and modifies whole taste nerve responses in bullfrogs. We increased the tonicity of stimulating solutions with non-taste substances such as urea or ethylene glycol. The hypertonicity enhanced phasic responses to NaCl>0.2M, and suppressed those to NaCl<0.1M, 1mM CaCl2, and 1mM bitter substances (quinine, denatonium and strychnine). The hypertonicity also enhanced the phasic responses to a variety of 0.5M salts such as LiCl and KCl. The enhancing effect was increased by increasing the difference between the ionic mobilities of the cations and anions in the salt. A preincubation time >20s in the presence of 1M non-taste substances was needed to elicit both the enhancing and suppressing effects. Lucifer Yellow CH, a paracellular marker dye, diffused into bullfrog taste receptor organs in 30s in the presence of hypertonicity. These results agreed with our proposed mechanism of hypertonic effects that considered the diffusion potential across open tight junctions.

Iontophoresis-targeted, follicular delivery of minoxidil sulfate for the treatment of alopecia

Although minoxidil (MX) is a drug known to stimulate hair growth, the treatment of androgenic alopecia could be improved by delivery strategies that would favor drug accumulation into the hair follicles. This work investigated in vitro the potential of iontophoresis to achieve this objective using MX sulfate (MXS), a more water-soluble derivative of MX. Passive delivery of MXS was first determined from an ethanol-water solution and from a thermosensitive gel. The latter formulation resulted in greater accumulation of MXS in the stratum corneum (skin's outermost layer) and hair follicles and an overall decrease in absorption through the skin. Anodal iontophoresis of MXS from the same gel formulation was then investigated at pH 3.5 and pH 5.5. Compared with passive delivery, iontophoresis increased the amount of drug reaching the follicular infundibula from 120 to 600 ng per follicle. In addition, drug recovery from follicular casts was threefold higher following iontophoresis at pH 5.5 compared with that at pH 3.5. Preliminary in vivo experiments in rats confirmed that iontophoretic delivery of MXS facilitated drug accumulation in hair follicles. Overall, therefore, iontophoresis successfully and significantly enhanced follicular delivery of MX suggesting a useful opportunity for the improved treatment of alopecia.

Enhanced transdermal permeability of estradiol using combination of PLGA nanoparticles system and iontophoresis

Estradiol is a therapeutic agent for treatment of perimenopausal symptoms and osteoporosis. Conventional oral or intravenous administration of estradiol has many problems, such as, metabolization in gastrointestinal tract and liver, pain by using an injection needle, rapid increase of drug levels in blood and fast clearance with unwanted side effects including thrombosis, endometriosis and uterus carcinoma. The use of nanocarriers for transdermal delivery has been studied because of their ability to deliver therapeutic agents for long time with a controlled ratio, escaping from the first pass effect by liver. In this study, permeability of estradiol-loaded PLGA nanoparticles through rat skin was studied. Higher amount of estradiol was delivered through skin when estradiol was loaded in nanoparticles than estradiol was free molecules. Also, iontophoresis was applied to enhance the permeability of nanoparticles. When iontophoresis was applied, permeability of estradiol-loaded PLGA nanoparticles was much higher than that obtained by simple diffusion of them through skin, since they have negative surface charges. They were found to penetrate through follicles mainly. Also, enhanced permeability effect of estradiol by using nanoparticle system and iontophoresis were observed in vivo. The combination of charged nanoparticle system with iontophoresis is useful for effective transdermal delivery of therapeutic agents.

Iontophoretic drug delivery across the nail

INTRODUCTION

Topical drug delivery to treat nail diseases such as onychomycosis and psoriasis is receiving increasing attention. Topical nail delivery is challenged by the complicated structure of the nail and the low permeability of most drugs across the nail plate. Considerable effort has been directed at developing methods to promote drug permeation across the nail plate. Iontophoresis efficiently enhances molecular transport across the skin and the eye and is now being tested for its potential in ungual delivery.

AREAS COVERED

This review covers the basic mechanisms of transport (electro-osmosis and -migration) and their relative contribution to nail iontophoresis as well as the key factors governing nail permselectivity and ionic transport numbers. Methodological issues concerning research in this area are summarized. The data available in vivo on nail iontophoresis of terbinafine specifically are reviewed in separate sections.

EXPERT OPINION

Our understanding of nail iontophoresis has improved considerably since 2007; most decisively, the feasibility of nail iontophoresis in vivo has been clearly demonstrated. Future work is required to establish the adequate implementation of the technique so that its clinical efficacy to treat onychomycosis and nail psoriasis can be unequivocally determined.

Enhanced transdermal delivery of indomethacin-loaded PLGA nanoparticles by iontophoresis

Nanoparticles effectively deliver therapeutic agent by penetrating into the skin. Indomethacin (IM) and coumarin-6 were loaded in PLGA nanoparticles with an average diameter of 100 nm. IM and coumarin-6 were chosen as a model drug and as a fluorescent marker, respectively. The surfaces of the nanoparticles were negatively charged. Permeability of IM-loaded PLGA nanoparticles through rat skin was studied. Higher amount of IM was delivered through skin when IM was loaded in nanoparticles than IM was free molecules. Also, iontophoresis was applied to enhance the permeability of nanoparticles. When iontophoresis with 3 V/cm was applied, permeability of IM was much higher than that obtained by simple diffusion of nanoparticles through skin. The combination of charged nanoparticle system with iontophoresis is useful for effective transdermal delivery of therapeutic agents.

Effect of iontophoresis on in vitro transdermal absorption of almotriptan

The aim of the present work was to characterize the in vitro transdermal absorption of almotriptan through pig ear skin. The passive diffusion of almotriptan malate and its iontophoretic transport were investigated using current densities of 0.25 and 0.50mA/cm(2). In vitro iontophoresis experiments were conducted on diffusion cells with an agar bridge without background electrolytes in the donor compartment. Although both current densities applied produced a statistically significant increment with respect to passive permeation of almotriptan (p<0.01), that of 0.50mA/cm(2) proved to be the best experimental condition for increasing the transport of almotriptan across the skin. Under these experimental conditions, the transdermal flux of the drug increased 411-fold with respect to passive diffusion, reaching 264±24μg/cm(2)h (mean±SD). Based on these results, and taking into account the pharmacokinetics of almotriptan, therapeutic drug plasma levels for the management of migraine could be achieved via transdermal iontophoresis using a reasonably sized (around 7.2cm(2)) patch.

Effective electrophoretic mobilities and charges of anti-VEGF proteins determined by capillary zone electrophoresis

Macromolecules such as therapeutic proteins currently serve an important role in the treatment of eye diseases such as wet age-related macular degeneration and diabetic retinopathy. Particularly, bevacizumab and ranibizumab have been shown to be effective in the treatment of these diseases. Iontophoresis can be employed to enhance ocular delivery of these macromolecules, but the lack of information on the properties of these macromolecules has hindered its development. The objectives of the present study were to determine the effective electrophoretic mobilities and charges of bevacizumab, ranibizumab, and model compound polystyrene sulfonate (PSS) using capillary zone electrophoresis. Salicylate, lidocaine, and bovine serum albumin (BSA), which have known electrophoretic mobilities in the literature, were also studied to validate the present technique. The hydrodynamic radii and diffusion coefficients of BSA, bevacizumab, ranibizumab, and PSS were measured by dynamic light scattering. The effective charges were calculated using the Einstein relation between diffusion coefficient and electrophoretic mobility and the Henry equation. The results show that bevacizumab and ranibizumab have low electrophoretic mobilities and are net negatively charged in phosphate buffered saline (PBS) of pH 7.4 and 0.16M ionic strength. PSS has high negative charge but the electrophoretic mobility in PBS is lower than that expected from the polymer structure. The present study demonstrated that capillary electrophoresis could be used to characterize the mobility and charge properties of drug candidates in the development of iontophoretic drug delivery.

A fast screening strategy for characterizing peptide delivery by transdermal iontophoresis

Capillary zone electrophoresis (CZE) is a convenient experimental tool for mimicking the low-throughput in vitro skin model used to optimize the delivery of peptides by transdermal iontophoresis. This paper is devoted to the extraction of pertinent molecular parameters from CZE experiments at different pH values, the optimization of CZE experimental conditions, and the development of an in silico filter useful for drug design and development. The effective mobility (mu(eff)) of ten model dipeptides was measured by CZE at different pH values, enabling to determine their pK(a) values, charge and mu(eff) at any pH. The best linear correlation between the electromigration contribution to transdermal iontophoretic flux (J(EM)) measured across porcine skin with donor and acceptor compartments at pH 7.4 and charge/MW ratio was obtained at pH 6.5, which seems to be the most suitable pH to mimic the in vitro skin model. Therefore, the experimental strategy can be considerably shortened by using a single mu(eff) measurement at pH 6.5 as a predictor of J(EM). Additionally, pK(a) prediction software packages offer a fast access to charge/MW ratio using consensual molecular charges at pH 6.5, which suggests that this simple in silico filter can be used as a preliminary estimation of J(EM).

In vitro optimization of dexamethasone phosphate delivery by iontophoresis

BACKGROUND AND PURPOSE

This study was designed to evaluate the effects of competing ions and electroosmosis on the transdermal iontophoresis of dexamethasone phosphate (Dex-Phos) and to identify the optimal conditions for its delivery.

METHODS

The experiments were performed using pig skin, in side-by-side diffusion cells (0.78 cm(2)), passing a constant current of 0.3 mA via Ag-AgCl electrodes. Dex-Phos transport was quantified for donor solutions (anodal and cathodal) containing different drug concentrations, with and without background electrolyte. Electrotransport of co-ion, citrate, and counterions Na(+) and K(+) also was quantified. The contribution of electroosmosis was evaluated by measuring the transport of the neutral marker (mannitol).

RESULTS

Electromigration was the dominant mechanism of drug iontophoresis, and reduction in electroosmotic flow directed against the cathodic delivery of Dex-Phos did not improve drug delivery. The Dex-Phos flux from the cathode was found to be optimal (transport number of approximately 0.012) when background electrolyte was excluded from the formulation. In this case, transport of the drug is limited principally by the competition with counterions (mainly Na(+) with a transport number of approximately 0.8) and the mobility of the drug in the membrane.

DISCUSSION AND CONCLUSION

Dex-Phos must be delivered from the cathode and formulated rationally, excluding mobile co-anions, to achieve optimal iontophoretic delivery.