Transdermal lontophoretic delivery of colchicine encapsulated in liposomes

An investigation into the combination of low frequency ultrasound and liposomes on skin permeability

Antigen application onto skin that has been pre-treated with low frequency ultrasound leads to immunisation, and it was hypothesised that immunisation could be enhanced if antigens were entrapped within liposomes, the latter being known vaccine adjuvants. However, it has been suggested that liposomes can repair skin damage, which could limit antigen permeation and transcutaneous immunisation. The aim of the present work was therefore to investigate the influence of liposome application on subsequent: (i) in vitro antigen permeation through, and (ii) in vivo barrier properties of, ultrasound-treated skin. Sonication was conducted using either phosphate buffered saline (PBS) or an aqueous solution of sodium dodecyl sulphate (SDS) as the coupling medium, and rats were used as the animal models. Liposome application to sonicated skin reduced antigen penetration and transepidermal water loss (TEWL, used as an indication of skin integrity) when the skin had been sonicated using PBS coupling medium. The influence of liposome was evident within 5min of its application, and smaller liposomes were more effective at repairing skin disruption caused by sonication. Such skin repair did not, however, take place when the skin had been sonicated in the presence of SDS (which caused greater skin disruption), and changes in in vitro antigen permeation and in vivo TEWL were negligible. Skin repair by liposomes seems to depend on the extent of the disruption caused by ultrasound application.

Transdermal iontophoresis

Iontophoresis is a technique used to enhance the transdermal delivery of compounds through the skin via the application of a small electric current. By the process of electromigration and electro-osmosis, iontophoresis increases the permeation of charged and neutral compounds, and offers the option for programmed drug delivery. Interest in this field of research has led to the successful delivery of both low (lidocaine) and high molecular drugs, such as peptides (e.g., luteinising hormone releasing hormone, nafarelin and insulin). Combinations of iontophoresis with chemical enhancers, electroporation and sonophoresis have been tested in order to further increase transdermal drug permeation and decrease possible side effects. In addition, rapid progress in the fields of microelectronics, nanotechnology and miniaturisation of devices is leading the way to more sophisticated iontophoretic devices, allowing improved designs with better control of drug delivery. Recent successful designing of the fentanyl E-TRANS iontophoretic system have provided encouraging results. This review will discuss basic concepts, principles and applications of this delivery technique.

Iontophoretic estradiol skin delivery and tritium exchange in ultradeformable liposomes

This work evaluated the in vitro transdermal iontophoretic delivery of tritiated estradiol from ultradeformable liposomes compared with saturated aqueous solution (control). Effects of current density and application time on tritium exchange with water were also determined. Penetration studies used three Protocols. Protocol I involved occluded passive steady state estradiol penetration from ultradeformable liposomes and control. The effect of current densities on drug penetration rates was also assessed (Protocol II). In Protocol III, three consecutive stages of drug penetration (first passive, iontophoresis and second passive) through the same human epidermal membranes were monitored. Such an experimental design investigated the possible effect of high current density (0.8 mA/cm(2)) on skin integrity. The tritium exchange study showed that extent of exchange correlated well with current density and time of application, with some shielding of estradiol by the liposomal structure. Liposomes enhanced estradiol passive penetration after occlusion. Protocol II showed that estradiol flux increased linearly with current density, although being delivered against electroosmotic flow. In Protocol III, reduction in flux of the second passive stage to near that of the first reflected a reversibility of the structural changes induced in skin by current.

Influence of lipids on the mannitol flux during transdermal iontophoresis in vitro

The aim of the present study was to evaluate the influence of the lipids EPC (L-alpha-phosphatidylcholine, egg lecithin), DSPC (distearoylphosphatidylcholine), and SA (stearylamine) on the iontophoretic mannitol transport through human skin in vitro. The skin was pretreated with 1 mM lipid suspension with ethanol (32%) for 24 h prior to the iontophoretic experiment with mannitol. In addition, the penetration of fluorescent lipids into the epidermis during the pretreatment was studied by confocal laser scanning microscopy (CLSM). The results of the present study show that pretreatment of the skin with zwitterionic EPC increases the iontophoretic transdermal mannitol flux about three-fold compared to iontophoretic control without pretreatment. However, skin pretreatment with another zwitterionic phospholipid, DSPC, did not influence the iontophoretic flux of mannitol. In contrast, pretreatment of the skin with cationic SA decreased the iontophoretic mannitol flow from the anode. It is concluded that EPC works as a penetration enhancer further increasing the transdermal mannitol flux during iontophoresis. In contrast, the cationic stearylamine changes the charge of the skin, thus leading to decreased electroosmosis and decreased mannitol flux. Hence, the effects of stearylamine are assumed to be mediated by the alterations in the charge of the stratum corneum structures, while EPC is suggested to decrease the permeability barrier of the skin.