Transdermal iontophoresis revisited

Iontophoresis evolved as a transdermal enhancement technique in the 20th century, primarily for the delivery of large and charged molecules. Significant achievements have been made in the understanding of underlying mechanisms of iontophoresis and these have contributed to the rational development of iontophoretic delivery systems. The major challenges in this area are the development of portable, cost effective devices and suitable semi-solid formulations that are compatible with the device and the skin. Some of the obstacles in transdermal iontophoresis can be overcome by combining iontophoresis with other physical and chemical enhancement techniques for the delivery of macromolecules. Iontophoresis also offers an avenue for extracting information from the body through the use of reverse iontophoresis, which has potential application in diagnosis and monitoring. The current research is focussed towards resolving the skin toxicity issues and other problems in order to make this technology a commercial reality.     

Enhancement of iontophoretic transport of diphenhydramine hydrochloride thermosensitive gel by optimization of pH, polymer concentration, electrode design, and pulse rate

The purpose of the present study was to explore the passive and electrically assisted transdermal transport of diphenhydramine hydrochloride (DPH) by iontophoresis. For better bioavailability, better patient compliance, and enhanced delivery of DPH, an iontophoretic drug delivery system of a thermosensitive DPH gel was formulated using Lutrol F-127. The study was conducted using silver-silver chloride electrodes across hairless pig skin. The effects of pH, polymer concentration, electrode design, and pulse rate on the DPH permeation were investigated. The relationship between temperature, viscosity, and conductance of DPH was correlated using conductometry. Iontophoretic transport of DPH was found to increase with a decrease in the pH of the medium and an increase in the surface area of the electrode. Viscosity measurements and flux calculations indicated the suitability of the Lutrol gel for transdermal iontophoretic delivery of DPH. Anodal pulsed iontophoresis with disc electrode significantly increased the DPH skin permeation as compared with the passive controls.     

Transport numbers in transdermal iontophoresis

Parameters determining ionic transport numbers in transdermal iontophoresis have been characterized. The transport number of an ion (its ability to carry charge) is key to its iontophoretic delivery or extraction across the skin. Using small inorganic ions, the roles of molar fraction and mobility of the co- and counterions present have been demonstrated. A direct, constant current was applied across mammalian skin in vitro. Cations were anodally delivered from either simple M(+)Cl(-) solutions (single-ion case, M(+) = sodium, lithium, ammonium, potassium), or binary and quaternary mixtures thereof. Transport numbers were deduced from ion fluxes. In the single-ion case, maximum cationic fluxes directly related to the corresponding ionic aqueous mobilities were found. Addition of co-ions decreased the transport numbers of all cations relative to the single-ion case, the degree of effect depending upon the molar fraction and mobility of the species involved. With chloride as the principal counterion competing to carry current across the skin (the in vivo situation), a maximum limit on the single or collective cation transport number was 0.6-0.8. Overall, these results demonstrate how current flowing across the skin during transdermal iontophoresis is distributed between competing ions, and establish simple rules with which to optimize transdermal iontophoretic transport.     

In vivo glucose monitoring: the clinical reality and the promise

Glucose monitoring is an essential component of modern diabetes management. Three in vivo glucose sensors are now available for clinical use: a subcutaneously implanted amperometric enzyme electrode, a reverse iontophoresis system and a microdialysis-based device. Improvements in glucose-sensing technology continue to be sought, e.g. wired enzyme technology, viscometric affinity sensing and totally implanted glucose sensors. Non-invasive glucose sensing is the ultimate goal of glucose monitoring, but the most investigated approach, near-infrared (NIR) spectroscopy, is presently too imprecise for clinical application. Fluorescence-based glucose sensing offers several advantages and we are investigating strategies which include NIR-based fluorescence resonance energy transfer using concanavalin A/dextran; changes in the intrinsic fluorescence of hexokinase encapsulated in sol-gel; and non-invasive glucose monitoring of cells by measuring glucose-related changes in NADP(H).     

Transdermal peptide delivery

The transdermal delivery of peptide drugs, though ill-favoured by their hydrophilicity and high molecular mass, would seem very attractive from the pharmacotherapeutical and patient compliance point of view. In some cases, effective transdermal dosing has been achieved in vivo, especially with the aid of iontophoresis. This paper deals with a dodecapeptide, des-enkephalin-gamma-endorphin, of which the transepidermal permeation and the intra(epi-)dermal biotransformation were both studied in vitro. Small, though measurable, fluxes through human stratum corneum were obtained in vitro, which could be enhanced by using a skin lipid fluidizer. The half-life of the peptide, both in the epidermis and in the dermis, was surprisingly long as compared with that in human plasma. Hence, improvement of the transdermal bioavailability of the peptide will most likely be obtained chiefly by enhancing its flux (possibly through iontophoresis), intra(epi-)dermal degradation being a problem of only minor importance.     

Electroosmosis in transdermal iontophoresis: implications for noninvasive and calibration-free glucose monitoring

Reverse iontophoresis uses a small low electric current to noninvasively extract blood analytes, e.g., glucose, across the skin. The simultaneous quantification of the analyte extracted and of an additional endogenous substance of fixed and known concentration in the body permits the blood level of interest to be found without the need for an invasive calibration procedure. The transport phenomena underlying this approach, applied to glucose monitoring, has been investigated in vitro, using Na+ and neutral model solutes as endogenous "internal standards" (specifically, urea, glycerol, mannitol, and sucrose). The cathodal extracted fluxes of glucose under conditions of modified skin permselectivity were related to those of the different, potential internal standards. Flux ratios depended upon the iontophoretic conditions and the size of the neutral internal standards, whereas high variability was observed with Na+. Constant flux ratios were obtained with mannitol, glycerol, urea, and sucrose for which the mechanism of electrotransport was identical to that of glucose. The advantage of using a neutral internal standard, however, must be weighed against the need to identify and validate the marker under physiological conditions and the additional analytical chemistry necessary for the practical quantification of this substance.     

An electrophoretic method to deliver topical drugs to the eye

It is possible that many patients avoid complete ophthalmic exams because pupil dilation is slow, reversal sluggish, and vision blurred. Others experience incomplete dilation during exams or prior to surgery when good dilation is essential to successful outcome. Iontophoresis, the application of low-level electrical current to promote traversal of desired molecules across a boundary, has been used for many years and has recently become common in transdermal drug delivery. We now investigate iontophoresis as a method of accelerating drug absorption into the ocular anterior segment. In vivo rabbit studies assessed iontophoresis effects on the performance of dilators and constrictors. 1-mA and 4-mA direct current levels applied for 2-minute durations yielded dilation time-history measurements. Subsequent in vitro tests at a wide range of current densities showed minimal chemical modifications in ocular pharmaceuticals. Drug samples processed through high-performance liquid chromatography (HPLC) pinpointed minimal structural changes. Detailed in vivo rabbit testing is under way. Using 2 dilators and constrictors in crossed testing with 0.5-mA to 1.25-mA current levels and 20-sec to 60-sec durations, we recorded dilation progress by digital photography. Initial studies showed faster, larger dilations and quicker reversal using iontophoresis. Drug testing showed chemical structures remaining constant for clinically useful current levels, < or = 1 mA (< or = 1.25 mA/cm2 current density). Drug pH and HPLC retention times were constant within this range, and resistivity varied linearly as expected for increasing current. Rabbit testing will quantify improved drug speed and efficacy, validate the charge delivery electrode design, and indicate iontophoretic current and duration for further use. Tested ocular drugs showed no degradation when exposed to clinically useful iontophoretic currents. Preliminary results indicate significant time reductions for dilation and reversal, plus increases in maximum dilation. This procedure may aid clinicians by allowing more rapid complete examinations and surgical preparations for patients. Making dilation more convenient will also improve patient acceptance of exams, aiding earlier detection and treatment of ocular disease.     

On-line determination of glucose and lactate concentrations in animal cell culture based on fibre optic detection of oxygen in flow-injection analysis.

A flow-injection analysis (FIA) system based on fibre optic detection of oxygen consumption using immobilized glucose oxidase (GOD) and lactate oxidase (LOD) is described for the on-line monitoring of glucose and lactate concentrations in animal cell cultures. The consumption of oxygen was determined via dynamic quenching by molecular oxygen of the fluorescence of an indicator. GOD and LOD were immobilized on controlled pore glass (CPG) in enzyme reactors which were directly linked to a specially designed fibre optic flow-through cell covering the oxygen optrode. The system is linear for 0-30 mM glucose, with an r.s.d. of 5% at 30 mM (five measurements) and for 0-30 mM lactate, with an r.s.d. of 5% at 30 mM (five measurements). The enzyme reactors used were stable for more than 4 weeks in continuous operation, and it was possible to analyse up to 20 samples per hour. The system has been successfully applied to the on-line monitoring of glucose and lactate concentrations of an animal cell culture designed for the production of recombinant human antithrombine III (AT-III). Results of the on-line measurement obtained by the FIA system were compared with the off-line results obtained by a glucose and lactate analyser from Yellow Springs Instrument Company (YSI).     

Hollow microneedle-based sensor for multiplexed transdermal electrochemical sensing

The development of a minimally invasive multiplexed monitoring system for rapid analysis of biologically-relevant molecules could offer individuals suffering from chronic medical conditions facile assessment of their immediate physiological state. Furthermore, it could serve as a research tool for analysis of complex, multifactorial medical conditions. In order for such a multianalyte sensor to be realized, it must be minimally invasive, sampling of interstitial fluid must occur without pain or harm to the user, and analysis must be rapid as well as selective. Initially developed for pain-free drug delivery, microneedles have been used to deliver vaccines and pharmacologic agents (e.g., insulin) through the skin. Since these devices access the interstitial space, microneedles that are integrated with microelectrodes can be used as transdermal electrochemical sensors. Selective detection of glucose, glutamate, lactate, hydrogen peroxide, and ascorbic acid has been demonstrated using integrated microneedle-electrode devices with carbon fibers, modified carbon pastes, and platinum-coated polymer microneedles serving as transducing elements. This microneedle sensor technology has enabled a novel and sophisticated analytical approach for in situ and simultaneous detection of multiple analytes. Multiplexing offers the possibility of monitoring complex microenvironments, which are otherwise difficult to characterize in a rapid and minimally invasive manner. For example, this technology could be utilized for simultaneous monitoring of extracellular levels of, glucose, lactate and pH, which are important metabolic indicators of disease states (e.g., cancer proliferation) and exercise-induced acidosis.     

Screening of Venlafaxine Hydrochloride for Transdermal Delivery: Passive Diffusion and Iontophoresis

The objective of the study was to investigate in vitro transdermal delivery of venlafaxine hydrochloride across the pigskin by passive diffusion and iontophoresis. For passive diffusion, experiments were carried out in Franz diffusion cell whereas for iontophoretic permeation, the diffusion cell was modified to contain both the donor and return electrode on the same side of skin. Anodal iontophoresis was carried out using a current density of 0.5 mA/cm². Donor concentrations used were 585.5 mg/ml (saturated solution) and 100 mg/ml. Experiments initially performed to determine the transport efficiency of venlafaxine ions showed promising results. Iontophoresis increased the permeation rate at both concentration levels over their passive counterparts (P < 0.01), but surprisingly higher steady-state flux was obtained from lower donor drug load (P < 0.01). The favorable pH of the unsaturated solutions is suggested to be the cause for this effect. Mild synergistic effect was observed when iontophoresis was carried out incorporating peppermint oil in the donor but the same was not found in passive diffusion. Highest steady-state flux obtained in the experiment was 3.279 μmol/cm²/h when peppermint oil (0.1%) was included in the donor. As the maintenance requirement of venlafaxine hydrochloride is approximately 9.956 μmol/h, the results suggested that the drug is a promising candidate for iontophoretic delivery.     

Continuous monitoring of blood glucose

Continuous blood glucose monitoring aims to: better evaluate glycaemic variations; better detect hypoglycaemia; and, ultimately, automatize insulin delivery (artificial beta cell). The sensors can be fully implantable, with the challenge of constructing durable systems to avoid repeated implantations. In-dwelling needle-like electrodes and microdialysis fibres with a pump that brings the dialysate to the glucose sensor are inserted in the subcutaneous tissue through the skin. The GlucoWatch is an almost non-invasive technique that extracts the extracellular fluid by iontophoresis. In these systems, the glucose oxidase generates the electrical signal, proportional to the glucose concentration. Non-invasive techniques aim at measuring the glucose concentration without breaching the skin, using absorption of light in the infrared spectrum. These techniques have not reached the necessary reliability for use as glycaemic alarms, and even less as artificial beta cells. Currently, glucose sensors are mainly used as glycaemic holters to help in the management of insulin therapy.     

Electric Stimulus Opens Intercellular Spaces in Skin

Iontophoresis is a technology for transdermal delivery of ionic small medicines by faint electricity. Since iontophoresis can noninvasively deliver charged molecules into the skin, this technology could be a useful administration method that may enhance patient comfort. Previously, we succeeded in the transdermal penetration of positively charged liposomes (diameters: 200–400 nm) encapsulating insulin by iontophoresis (Kajimoto, K., Yamamoto, M., Watanabe, M., Kigasawa, K., Kanamura, K., Harashima, H., and Kogure, K. (2011) Int. J. Pharm. 403, 57–65). However, the mechanism by which these liposomes penetrated the skin was difficult to define based on general knowledge of principles such as electro-repulsion and electro-osmosis. In the present study, we confirmed that rigid nanoparticles could penetrate into the epidermis by iontophoresis. We further found that levels of the gap junction protein connexin 43 protein significantly decreased after faint electric stimulus (ES) treatment, although occludin, CLD-4, and ZO-1 levels were unchanged. Moreover, connexin 43 phosphorylation and filamentous actin depolymerization in vivo and in vitro were observed when permeation of charged liposomes through intercellular spaces was induced by ES. Ca²⁺ inflow into cells was promoted by ES with charged liposomes, while a protein kinase C inhibitor prevented ES-induced permeation of macromolecules. Consequently, we demonstrate that ES treatment with charged liposomes induced dissociation of intercellular junctions via cell signaling pathways. These findings suggest that ES could be used to regulate skin physiology.     

Application of L-(+)-Lactate electrode for clinical analysis and monitoring of tissue culture medium

L-(+)-Lactate oxidase (EC 1.1.3.2) was immobilized onto the porous side of a cellulose acetate membrane with asymmetric structure which has selective permeability to hydrogen peroxide. The lactate electrode was constructed by combination of a hydrogen peroxide electrode with the immobilized enzyme membrane. Properties of the enzyme membrane and characteristics of the lactate electrode were clarified for the determination of L-(+)-lactic acid. The lactate electrode responded linearly to L-(+)-lactic acid over the final concentration 0-0.25 mmol/L within 30 s. When the enzyme electrode was applied to the determination of L-(+)-lactic acid in control serum, within-day precision (CV), analytical recovery, and correlation coefficient between the electrode method and the colorimetric method were 1.4% with a mean value of 4.54 mmol/L, 98.0%, and 0.986, respectively. The lactate electrode was sufficiently stable to perform 1040 assays over 13 days operation for the determination of L-(+)-lactic acid. The dried immobilized enzyme membrane retained 84% of its initial activity after storage at 4 degrees C for 12 months. Moreover, the enzyme electrode was applied to the monitoring of culture medium for human melanoma cells. L-(+)-Lactate production and D-glucose consumption were closely related to cell numbers.     

Glycolysis as a metabolic marker in orthotopic breast cancer,monitored by in vivo (13)C MRS

Enhanced glycolysis represents a striking feature of cancers and can therefore serve to indicate a malignant transformation. We have developed a noninvasive, quantitative method to characterize tumor glycolysis by monitoring (13)C-labeled glucose and lactate with magnetic resonance spectroscopy. This method was applied in MCF7 human breast cancer implanted in the mammary gland of female CD1-NU mice and was further employed to assess tumor response to hormonal manipulation with the antiestrogen tamoxifen. Analysis of the kinetic data based on a unique physiological-metabolic model yielded the rate parameters of glycolysis, glucose perfusion, and lactate clearance in the tumor, as well as glucose pharmacokinetics in the plasma. Treatment with tamoxifen induced a twofold reduction in the rate of glycolysis and of lactate clearance but did not affect the other parameters. This metabolic monitoring can thus serve to evaluate the efficacy of new selective estrogen receptor modulators and may be further extended to improve diagnosis and prognosis of breast cancer.     

Perspectives on transdermal ultrasound mediated drug delivery

The use of needles for multiple injection of drugs, such as insulin for diabetes, can be painful. As a result, prescribed drug noncompliance can result in severe medical complications. Several noninvasive methods exist for transdermal drug delivery. These include chemical mediation using liposomes and chemical enhancers or physical mechanisms such as microneedles, iontophoresis, electroporation, and ultrasound. Ultrasound enhanced transdermal drug delivery offers advantages over traditional drug delivery methods which are often invasive and painful. A broad review of the transdermal ultrasound drug delivery literature has shown that this technology offers promising potential for noninvasive drug administration. From a clinical perspective, few drugs, proteins or peptides have been successfully administered transdermally because of the low skin permeability to these relatively large molecules, although much work is underway to resolve this problem. The proposed mechanism of ultrasound has been suggested to be the result of cavitation, which is discussed along with the bioeffects from therapeutic ultrasound. For low frequencies, potential transducers which can be used for drug delivery are discussed, along with cautions regarding ultrasound safety versus efficacy.     

Local heating of human skin causes hyperemia without mediation by muscarinic cholinergic receptors or prostanoids.

Local changes in surface temperature have a powerful influence on the perfusion of human skin. Heating increases local skin blood flow, but the mechanisms and mediators of this response (thermal hyperemia response) are incompletely elucidated. In the present study, we examined the possible dependence of the thermal hyperemia response on stimulation of muscarinic cholinergic receptors and on production of vasodilator prostanoids. In 13 male healthy subjects aged 20-30 yr, a temperature-controlled chamber was positioned on the volar face of one forearm and used to raise surface temperature from 34 to 41 degrees C. The time course of the resulting thermal hyperemia response was recorded with a laser-Doppler imager. In one experiment, each of eight subjects received an intravenous bolus of the antimuscarinic agent glycopyrrolate (4 microg/kg) on one visit and saline on the other. The thermal hyperemia response was determined within the hour after the injections. Glycopyrrolate effectively inhibited the skin vasodilation induced by iontophoresis of acetylcholine but did not influence the thermal hyperemia response. In a second experiment, conducted in five other subjects, 1 g of the cyclooxygenase inhibitor aspirin administered orally totally abolished the vasodilation induced in the skin by anodal current but also failed to modify the thermal hyperemia response. The present study excludes the stimulation of muscarinic receptors and the production of vasodilator prostaglandins as essential and nonredundant mechanisms for the vasodilation induced by local heating in human forearm skin.     

二次谐波结合双光子荧光成像方法观察人源胶原蛋白透皮吸收情况

目的:用二次谐波成像结合双光子荧光成像的方法观察人源胶原蛋白透皮吸收的情况。方法:将荧光标记的人源胶原蛋白(1 mg/mL)涂抹于小鼠表皮层经皮肤吸收1 h后用背向二次谐波观察皮肤内胶原纤维作为真皮层定位标志,用双光子扫描共聚焦显微镜观察人源胶原蛋白透皮吸收深度,吸收方式。结果:二次谐波成像结合双光子荧光成像表明人源胶原蛋白透皮吸收1 h后可观察到荧光信号沿着毛囊聚集,并有部分荧光分子由毛囊扩散至真皮层。结论:二次谐波可以更快速,更灵敏地检测皮肤中的胶原纤维,以此作为检测物质透皮吸收深度的定位标志,具有不受荧光信号干扰的优点。人源胶原蛋白可以沿着毛囊进入真皮层,并从毛囊中扩散至胶原纤维层从而补充皮肤中的胶原纤维。     

Iontophoresis of endothelin receptor antagonists in rats and men

Introduction

The treatment of scleroderma-related digital ulcers is challenging. The oral endothelin receptor antagonist (ERA) bosentan has been approved but it may induce liver toxicity. The objective of this study was to test whether ERAs bosentan and sitaxentan could be locally delivered using iontophoresis.

Methods

Cathodal and anodal iontophoresis of bosentan and sitaxentan were performed on anaesthetized rat hindquarters without and during endothelin-1 infusion. Skin blood flow was quantified using laser-Doppler imaging and cutaneous tolerability was assessed. Iontophoresis of sitaxentan (20 min, 20 or 100 µA) was subsequently performed on the forearm skin of healthy men (n = 5).

Results

In rats neither bosentan nor sitaxentan increased skin blood flux compared to NaCl. When simultaneously infusing endothelin-1, cathodal iontophoresis of sitaxentan increased skin blood flux compared to NaCl (AUC_0–20 were 44032.2±12277 and 14957.5±23818.8 %BL.s, respectively; P = 0.01). In humans, sitaxentan did not significantly increase skin blood flux as compared to NaCl. Iontophoresis of ERAs was well tolerated both in animals and humans.

Conclusions

This study shows that cathodal iontophoresis of sitaxentan but not bosentan partially reverses endothelin-induced skin vasoconstriction in rats, suggesting that sitaxentan diffuses into the dermis. However, sitaxentan does not influence basal skin microvascular tone in rats or in humans.     

Influence of vehicle resistance on transdermal iontophoretic delivery of acetylcholine and sodium nitroprusside in humans.

Iontophoresis is a valuable method of noninvasive drug delivery for assessment of skin microvascular function, but it is important to consider and minimize its potential nonspecific electrical effects on blood flow. The use of sodium chloride (NaCl) instead of water as the iontophoresis vehicle has been reported to reduce these effects because it has a lower electrical resistance. However, this argument may not be valid when an agonist is added to the vehicle because its resistance will be changed. The aim of our study was to determine whether there is a difference in resistance between water and NaCl when used as vehicles for iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP). Four cumulative doses of each drug, dissolved in either water or NaCl, were delivered via iontophoresis to the forearm skin of 14 healthy volunteers. We measured the resulting blood flow responses by using laser-Doppler imaging and the voltage across the electrodes for each delivery as an index of resistance. For ACh and SNP, there were no significant differences between the voltages measured when either water or NaCl was used as the vehicle. However, the blood flow responses to both agonists were significantly lower with NaCl (ACh: 25% lower, P < 0.001; SNP: 15% lower, P = 0.019). The use of NaCl is therefore unlikely to decrease any nonspecific electrical effects, and it may in fact reduce the effective dose of drug delivered. Deionized water is a better iontophoresis vehicle for the assessment of microvascular function in skin when using ACh and SNP.     

Elastic Vesicles as a Tool for Dermal and Transdermal Delivery

The main problem in delivery of drugs across the skin is the barrier function of the skin, which is located in the outermost layer of the skin, the stratum corneum. The stratum corneum consists of corneocytes surrounded by lipid layers, the so-called lipid lamellae. When applying drugs onto the skin, the major penetration pathway is the tortuous intercellular route along the lipid lamellae. In order to increase the number of drugs administered via the transdermal route, novel drug delivery systems have to be designed. Among these systems are iontophoresis, electroporation, microneedles, and vesicular systems.