Transdermal lontophoretic Delivery of Luteinizing Hormone Releasing Hormone (LHRH): Effect of Repeated Administration

The transdermal iontophoretic delivery of the reproductive peptide hormone, luteinizing hormone releasing hormone (LHRH) is investigated in the isolated perfused porcine skin flap model (IPPSF). LHRH is delivered twice in a single flap experiment in efforts to identify factors inherent to iontophoretic delivery that might effect the drug flux of a subsequent iontophoretic episode. Initial iontophoretic delivery of LHRH is quite reproducible; however, subsequent iontophoretic episodes result in widely divergent fluxes thought to be caused by iontophoretic influences on the skin. Iontophoretic application of a drug on a previous active site, enhances the flux during the second application. A mass balance study is performed to explain these findings. By iontophoretically delivering I¹²⁵ labelled LHRH in the isolated perfused porcine skin flap model, the entire iontophoretic dose is identified and quantified. A drug depot is identified in the skin underlying the electrode which is approximately two times as large as the entire mass of drug delivered systemically.     

Transdermal Delivery of Fentanyl by Electroporation I. Influence of Electrical Factors

Purpose. Electroporation, a method of reversibly permeabilizing lipid bilayers by the application of an electric pulse, has been shown to induce increased transdermal passage of molecules. The aim of the present report was to study in vitro with hairless rat skin the potential of electroporation for transdermal delivery of fentanyl. Results. The application of electric pulses can strongly promote transdermal delivery of fentanyl compared to passive diffusion through untreated skin. We also point out that the choice of the waveform of the electric pulses is important: at the same applied energy, a few exponentially-decaying (ED) pulses increased fentanyl permeation more than a few square-wave pulses and to the same extent as the repeated application of higher voltage-shorter duration ED pulses. A factorial design showed that the voltage, duration, and number of ED pulses allowed control of the quantity of drug transported through the skin. Conclusions. Skin electroporation could be a good way to improve the transdermal diffusion of fentanyl.     

LHRH离子电渗透皮给药系统的研究I.LHRH的离子电渗透皮吸收

研究了影响ＬＨＲＨ体子电渗透过裸鼠皮肤的因素。发现２５００ＨＺ（占空比３：１）的方波电流体外透皮效果最好，且透皮速率随着电流密度的增加而增加。ＬＨＲＨ在皮肤中会滞留，外加电场撤去后，ＬＨＲＨ仍持续透过。采用交变电渗技术可以达到脉冲电渗效果。因而可模拟ＬＨＲＨ体内分泌的模式     

电致孔技术在透皮给药中的应用

电致孔可显著提高药物的经皮吸收,有望用于多肽和蛋白质类生物大分子药物的透皮给药.本文对电致孔法的透皮促渗机制、影响因素以及安全性进行了讨论,并介绍了有关实验装置及其在透皮给药中的应用.     

Transdermal Delivery of Macromolecules Using Skin Electroporation

Purposes. (1) To evaluate the feasibility of transdermal delivery ofmacromolecules by skin electroporation. (2) To assess the influenceof the molecular weight of the permeant on transport and examinewhether there exists a cut-off value of molecular weight. (3) Tolocalize the transport pathways of the macromolecules in the skin. Methods. FITC-dextran (FD) of increasing molecular weight (4.4, 12and 38 kDa) were used as model macromolecules to study the extentof transport across hairless rats skin in vitro and to localize theirdistribution in the skin by confocal scanning laser microscopy. Results. Electroporation enhanced the transport of the macromoleculesas compared to passive diffusion. The transdermal delivery by skinelectroporation of FITC and FD 4.4 was equivalent whereas transportof higher molecular weight FD was lower but significant. FITC and FD38 were observed in the epidermis both around and in the keratinocytes. Conclusions. Transdermal and topical delivery of macromolecules ofat least 40 kDa can be achieved by skin electroporation.     

Rapid Temporal Control of Transdermal Drug Delivery by Electroporation

Pharmaceutical Research -     

Transdermal Delivery of Metoprolol by Electroporation

Electroporation, i.e., the creation of transient pores in lipid membranes leading to increased permeability, could be used to promote transdermal drug delivery. We have evaluated metoprolol permeation through full thickness hairless rat skin in vitro following electroporation with an exponentially decaying pulse. Application of electric pulses increased metoprolol permeation as compared to diffusion through untreated skin. Raising the number of twin pulses (300 V, 3 ms; followed after 1 s by 100 V, 620 ms) from 1 to 20 increased drug transport. Single pulse (100 V, 620 ms) was as effective as twin pulse application (2200 V, 1100 V or 300 V, 3 ms; followed after 1 s by 100 V, 620 ms). In order to investigate the effect of pulse voltage on metoprolol permeation, 5 single pulses (each separated by 1 min) were applied at varying voltages from 24 to 450 V (pulse time 620 ms). A linear correlation between pulse voltage and cumulative metoprolol transported after 4 h suggested that voltage controls the quantity of drug delivered. Then, the effect of pulse time on metoprolol permeation was studied by varying pulse duration of 5 single 100 V pulses from 80 to 710 ms (each pulse also separated by 1 min). Cumulative metoprolol transported after 4 h increased linearly with the pulse time. Therefore, pulse time was also a control factor of the quantity of drug delivered but to a lesser extent than the voltage at least at 100 V. The mechanisms behind improved transdermal drug delivery by electroporation involved reversible increased skin permeability, electrophoretic movement of drug into the skin during pulse application, and drug release from the skin reservoir formed by electroporation. Thus, electroporation did occur as shown by the increased transdermal permeation, on indicator of structural skin changes and their reversibility. Electroporation has potential for enhancing transdermal drug delivery.     

胰岛素脂质体的制备及在电致孔下的经皮渗透

采用反相蒸发法制备了平均粒径122.7nm的胰岛素脂质体,并考察了电致孔经皮转运情况.结果表明,在电致孔条件下,胰岛素脂质体2h累积渗透量是载药脂质体被动扩散的1倍;是原药及其与空白脂质体混合物的2～3倍.     

电致孔对睾酮透皮转运的影响

研究了电致孔技术对睾酮透皮转运的影响,对电压、脉冲持续时间和电极的影响进行了初步探讨.结果表明,电致孔可增大药物的透皮转运速率及其累积透过量,且电力学参数与透皮吸收增量呈正相关,电极也明显影响电致孔透皮速率.     

Electrically-Assisted Transdermal Drug Delivery

Electrically-assisted transdermal delivery (EATDD) is the facilitated transport of compounds across the skin using an electromotive force. It has been extensively explored as a potential means for delivering peptides and other hydrophilic, acid-labile or orally unstable products of biotechnology. The predominant mechanism for delivery is iontophoresis, although electroosmosis and electroporation have also been investigated. The focus of this review is to put these different mechanisms in perspective and relate them to the drug and skin model system being investigated.     

Transdermal Delivery of Fentanyl by Electroporation II. Mechanisms Involved in Drug Transport

Purpose. The aim of the present report was to systematically analyze the mechanisms involved in fentanyl transdermal transport by skin electroporation. Methods. The study was performed in vitro with full-thickness hairless rat skin, skin electroporation being carried out with five exponentially-decaying pulses of 100 V applied voltage and around 600 ms pulse duration. Results. Transport during and after pulsing are both important in transdermal delivery of fentanyl by skin electroporation. Rapid transport occurred during pulsing due to electrophoresis and diffusion through highly permeabilized skin. No electroosmosis was observed. The slow post-pulse passive transport was explained by lasting changes in skin permeability. Measurements of fentanyl quantities in the skin demonstrated that pulses rapidly loaded the viable part of the skin with fentanyl and hence rapidly overcame skin barrier. Conclusions. The different contributions of the transport mechanisms appear to depend on the physicochemical parameters of the transported molecule as well as the solution, suggesting that mechanistic analysis and careful consideration of formulation variables are essential for the development and optimization of drug delivery by skin electroporation.     

lontophoretic Delivery of a Series of Tripeptides Across the Skin in Vitro

The iontophoresis of eight tripeptides, of the general structure alanine–X–alanine, has been measured across hairless mouse skin in vitro. The peptides were blocked (a) at the carboxyl terminus using the mixed anhydride reaction with t-butylamine and (b) at the amino terminus by acetylation with ¹⁴C-acetic anhydride. The nature of the central residue (X) was varied by selecting one of five neutral amino acids, two negatively chargeable moieties (aspartic and glutamic acids), and a positively chargeable species (histidine). Constant current iontophoresis at 0.36 mA/cm², using Ag/AgCl electrodes, was performed for 24 hr in diffusion cells, which allowed both anode and cathode to be situated on the same (epidermal) side of a single piece of skin. Due to a combination of osmotic and electroosmotic forces, the anodal iontophoretic flux of neutral peptides was significantly greater than passive transport. Steady-state fluxes were not achieved, however, suggesting that time-dependent changes in the properties of the skin barrier may be occurring. Limited, further experiments confirmed that, on a 24-hr time scale, these changes were not fully reversible. The cathodal delivery of anionic permeants was well controlled at a steady and highly enhanced rate by the current flow. This behavior closely paralleled earlier work using simple negatively charged amino acids and N-acetylated amino acid derivatives. It appears that the normalized iontophoretic flux of these anionic species is independent of lipophilicity but may be inversely related to molecular weight. The positively charged peptide, Ac–Ala–His–Ala–NH(Bu^t), showed greater anodal iontophoretic enhancement when delivered from a donor solution at pH 4.0 than from a solution at pH 7.4. This was consistent with (a) the corresponding behavior of histidine alone and (b) the existence of a pK _a for these compounds at 6. Steady-state delivery was not achieved, although the levels of enhancement, especially at pH 4, were the largest observed. A preliminary investigation of tripeptide stability to either (i) electrolysis in the donor compartment or (ii) cutaneous metabolism revealed very little degradation under the conditions of the experiment. Overall, this research supports the principle of enhanced peptide delivery across the skin by iontophoresis and indicates a number of areas (e.g., mechanism and extent of current-induced changes in skin barrier function, molecular size dependence, pathways of current flow) on which further work should be focused.     

Ionized Prodrugs of Dehydroepiandrosterone for Transdermal lontophoretic Delivery

Purpose. The aim of this work was to synthesize ionized dehydroepiandrosterone (DHEA) prodrugs with higher water solubility, useful for iontophoretic transdermal application. Methods. The synthesized derivatives were characterized and tested for sensitivity to chemical and enzymatic hydrolysis. Solid state and solution stability was also determined. Transdermal iontophoretic anodal transport in vitro was studied using excised rabbit skin. Results. Two DHEA ionized prodrugs were synthesized: PRO1, a primary amine derivative, and PRO2, a quaternary ammonium salt. The two derivatives possess higher water solubility and lower octanol/saline partition coefficients than DHEA. Prodrugs were sensitive to enzymatic hydrolysis; in particular the primary amine was hydrolyzed faster than the quaternary salt by esterase from porcine liver in vitro. Transdermal flux of the two prodrugs was slightly higher than the parent drug. In the case of passive diffusion, only DHEA was found in the receptor compartment, indicating the complete breakdown of the prodrug in the skin. Current application gave higher drug flux and a significant amount of prodrug was found in the receptor. Conclusions. The use of ionized prodrugs of DHEA can increase the flux attainable during transdermal anodal iontophoresis by up to 7 times, but they are useful for passive transport as well.     

lontophoretic Delivery of a Telomeric Oligonucleotide

Purpose. To evaluate the feasibility of iontophoretically enhanced transdermal delivery of a phosphorothioate oligonucleotide across hairless mouse skin. Methods. The phosphorothioate sequence, 5-d(TTAGGG)-3 (TAG-6) which mimics the repeat sequence of the telomere was used as a model compound. Iontophoresis was performed on hairless mouse skin using an in vitro flow-through diffusion system. Both 5-FITC and uniformly ³⁵S labeled oligonucleotide were used to monitor transdermal flux. Results. Cathodal delivery of TAG-6 resulted in substantial oligonucleotide flux. The molecular label did not alter transport properties. No flux was measured with either anodal or passive delivery. The oligonucleotide was not degraded as it crossed the skin. Molecular transport was donor condition dependent, with pH and salt concentration both having significant effects. Pre-treating the skin with ethanol reduced iontophoretic transport. Conclusions. These data demonstrate that iontophoresis can enhance transdermal flux of an intact phosphorothioate oligonucleotide and that this penetration is donor condition dependent. Furthermore, iontophoretically enhanced transdermal delivery is a feasible apprach to the administration of phosphorothioate oligonucleotides.     

lontophoretic Delivery of Amino Acids and Amino Acid Derivatives Across the Skin in Vitro

The effects of penetrant properties (lipophilicity and charge) and of vehicle pH on the iontophoretically enhanced delivery of amino acids and their N-acetylated derivatives have been examined in vitro. The penetrants were nine amino acids (five were zwitterionic, two positively charged, and two negatively charged) and four N-acetylated amino acids, which carry a net negative charge at pH 7.4. Iontophoresis at constant current (0.36 mA/cm²), using Ag/AgCl electrodes, was conducted across freshly excised hairless mouse skin. Iontophoretic flux of the zwitterions was significantly greater than passive transport. Delivery from the anode was greater than from the cathode for all zwitterions. The level of enhancement was inversely proportional to permeant octanol/pH 7.4 buffer distribution coefficient. Cathodal iontophoresis of the negatively charged amino acids and of the N-acetylated derivatives produced degrees of enhancement which were significantly greater than those measured for the neutral zwitterions. Furthermore, the enhanced flux reached a steady-state level within a few hours for the negatively charged species, whereas the transport of the zwitterions continued to increase with time. Anodal iontophoresis of histidine and lysine, the two positively charged amino acids studied, induced substantial enhancement which was sensitive to the pH of the delivery vehicle. For example, the flux of histidine from an applied solution at pH 4 (where the amino acid carries a net positive charge) was significantly greater than that from a vehicle at pH 7.4 (where histidine is essentially neutral). The behavior of lysine was more complex and suggested a certain degree of neutralization of the skin's net negative charge.     

Electrically Modulated Transdermal Delivery of Fentanyl

Purpose. Test to determine if iontophoresis and electroporation, alone or in combination, can be used for rapid and modulated delivery of fentanyl. Methods. Fentanyl citrate (5 mg/ml) dissolved in pH 4.0 citrate buffer was delivered in vitro across human epidermis. For iontophoresis, a current of 0.5 mA/cm² was applied for 5 h, using silver/silver chloride electrodes. Electroporation protocol consisted of applying 15 exponential pulses of 500V (applied voltage) and 200 msec duration at the rate of 1 pulse per minute at time zero and, in some cases, repeating at 1.5 and 2.5 h. Results. There was no measurable permeation of fentanyl through human epidermis under passive conditions. A significant flux (about 80 g/cm²-hr) was achieved using iontophoresis and decreased once the current was turned off. A 4-fold higher flux and shorter lag time was observed with electroporation as compared to iontophoresis. The flux was found to recover quickly (within 1 h) following pulsing. Modulation of transdermal delivery of fentanyl was demonstrated by both iontophoresis and electroporation. Conclusions. Electrically assisted transdermal delivery of fentanyl significantly increased transport compared to passive delivery. Also, rapid and modulated delivery was shown to be feasible by programming the electrical parameters.     

电场方向对电穿孔技术促进咖啡因经皮渗透的影响

目的研究电场方向对电穿孔技术促进咖啡因经皮渗透的影响。方法应用水平双室扩散池,Ag-Ag/AgCl电极和人尸体皮肤,进行咖啡因的经皮渗透实验,考察电场方向对电穿孔(指数衰减型脉冲,脉冲幅度为350 V,脉冲率为4 pulses·min-1,脉冲数为25,电容为22μF )促渗作用的影响,并与离子导入(0.25 mA·cm-2,持续4小时)进行比较。结果 1)电穿孔与离子导入均可显著增加咖啡因的经皮渗透速率和累积渗透量。2)阳极离子导入(电场方向为从供应室到接受室)的促渗作用显著大于阴极离子导入(电场方向为从接受室到供应室)的促渗作用。3)阳极电穿孔的促渗作用与阴极电穿孔的促渗作用无显著差异。4)阳极离子导入的促渗作用显著大于阳极电穿孔及阴极电穿孔的促渗作用。结论电场方向对离子导入的促渗作用有显著影响,而对电穿孔的促渗作用没有影响。     

Current Status and Future Prospects of Transdermal Drug Delivery

Pharmaceutical Research -     

Synergistic Effect of Enhancers for Transdermal Drug Delivery

Transdermal drug delivery offers a non-invasive route of drug administration, although its applications are limited by low skin permeability. Various enhancers including iontophoresis, chemicals, ultrasound, and electroporation have been shown to enhance transdermal drug transport. Although all these methods have been individually shown to enhance transdermal drug transport, their combinations have often been found to enhance transdermal transport more effectively than each of them alone. This paper summarizes literature studies on these combinations with respect to their efficacy and mechanisms.     

电穿孔技术促进萘普生经皮渗透的研究

目的：研究电穿孔技术对小分子离子型药物经皮渗透的影响。方法：应用双室扩散池方法研究电穿孔技术对萘普生在离体大鼠腹部皮肤经皮渗透的影响。并与被动扩散和离子导入进行比较。结果：外加电脉冲（指数衰减型脉冲,脉冲幅度为４００Ｖ,电容器电容为２．２ｕＦ,脉冲率为２０ｐｕｌｓｅｓ．ｍｉｎ＾－１,脉冲宽度τ≈６．０ｍｓ）或离子导入（１ｍＡ．ｃｍ＾－２,６ｈ）时,萘普生的渗透速率和累积渗透量均大于被动扩散。外加脉