Iontophoretic and chemical enhancement of drug delivery. Part I: across artificial membranes

Reverse Iontophoretic Extraction of Skin Cancer-Related Biomarkers

Non-invasive methods for early diagnosis of skin cancer are highly valued. One possible approach is to monitor relevant biomarkers such as tryptophan (Trp) and kynurenine (Kyn), on the skin surface. The primary aim of this in vitro investigation was, therefore, to examine whether reverse iontophoresis (RI) can enhance the extraction of Trp and Kyn, and to demonstrate how the Trp/Kyn ratio acquired from the skin surface reflects that in the epidermal tissue. The study also explored whether the pH of the receiver medium impacted on extraction efficiency, and assessed the suitability of a bicontinuous cubic liquid crystal as an alternative to a simple buffer solution for this purpose. RI substantially enhanced the extraction of Trp and Kyn, in particular towards the cathode. The Trp/Kyn ratio obtained on the surface matched that in the viable skin. Increasing the receiver solution pH from 4 to 9 improved extraction of both analytes, but did not significantly change the Trp/Kyn ratio. RI extraction of Trp and Kyn into the cubic liquid crystal was comparable to that achieved with simple aqueous receiver solutions. We conclude that RI offers a potential for non-invasive sampling of low-molecular weight biomarkers and further investigations in vivo are therefore warranted.

Combined effects of iontophoretic and chemical enhancement on drug delivery

This paper reports measurements of the release characteristics of the model drug salbutamol from a liquid crystalline vehicle across both human and hairless murine skin in vitro. The use of oleic acid and iontophoresis as penetration enhancement techniques, used separately and simultaneously, was also investigated. Over a period of 12h, salbutamol base did not diffuse from the vehicle across excised human skin while, in contrast, over a period of 2h, the drug passively transported across hairless murine skin. The diffusion co-efficient for the drug in this tissue was estimated to be 4.54+/-0.60x10(-9)cm(2)s(-1) with a permeability co-efficient of 7.03+/-0.83x10(-7)cms(-1). A current of density of 0.39mAcm(-2) facilitated a significant transport of salbutamol from the liquid crystalline vehicle across excised human skin but with a small (<0.1) transport number. The quantity of salbutamol transported across excised hairless murine skin under the same conditions was significantly greater with a transport number of 0.68. The alteration of the permeability of the tissue was less than that of the human skin and a full recovery of the pre-iontophoretic permeability of murine skin was consistently observed. The incorporation of either oleic or lauric acid into the monoglyceride component of the vehicle at a concentration of 0.1M had a marked effect on the transport of salbutamol across both human and murine skin. The initial passive permeation of the drug across the skin was not affected but the rate of drug delivery during iontophoresis was typically observed to increase by a factor greater than two. The post-iontophoretic transport of salbutamol across either tissue was also substantially enhanced in the presence of the fatty acid. The analogous use of stearic acid did not significantly influence the iontophoretic or the post-iontophoretic transport of salbutamol across excised human skin. The investigation also revealed a synergistic combination of the fatty acid and anodal iontophoresis to enhance the in vitro transport of other drug substances, including nicotine and diltiazem hydrochloride across murine skin. Oleic acid increased both the iontophoretic and post-iontophoretic transport of nicotine, so that the enhancement of drug delivery was greater than that caused by the current alone. The investigation also indicated that the barrier properties of the skin recover following the constant current iontophoresis in the presence of oleic or lauric acids.

Release characteristics of anionic drug compounds from liquid crystalline gels

This paper investigates the release and transport of a range of anionic drugs from liquid crystalline gels using chemical and physical enhancement techniques. Previous papers [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels. I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236; Fitzpatrick, D., Corish, J., 2006. Release characteristics of anionic drug compounds from liquid crystalline gels. II. The effects of ion pairing and buffering on the passive delivery of anionic drugs across non rate-limiting membranes. Int. J. Pharm.] have reported on the passive release profiles and those resulting from the incorporation of a chemical enhancer in the vehicle. This paper investigates the behaviour of the system under iontophoretic conditions and also under those of combined physical and chemical enhancement. The data presented here are directly comparable to previous work by Nolan et al. [; Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2006. Combined effects of iontophoretic and chemical enhancement on drug delivery. II. Transport across human and hairless murine skin. Int. J. Pharm., submitted for publication] which investigated the behaviour of cationic compounds under analogous conditions. The iontophoretic release of diclofenac in the presence of model enhancers is thoroughly investigated. It is also shown that a range of anionic drug molecules undergo an electrochemical change during the course of the experiments which leads to their poor detection. This may be a factor in the under reporting of iontophoretic delivery of anionic drugs in the literature. However, it has been shown that the transport of the drugs is greatly enhanced by the application of an iontophoretic current. Results of combined enhancement studies provide a positive basis on which to proceed with in vitro studies of the system across human skin.

Release characteristics of anionic drug compounds from liquid crystalline gels

This is the second in a series of papers that report on the release and transport of a range of anionic drugs (diclofenac, salicylic acid) from liquid crystalline gels and ultimately on their use in transdermal delivery. The previous paper [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels for transdermal delivery. Part I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236] investigated passive release profiles across a non-rate-limiting membrane: here we report on the search for a suitable model enhancer (benzyl dimethyldodecyl ammonium bromide) for the transdermal delivery of anionic compounds. The results presented reveal a significant role for ion pairing and for buffering, analogous to those found in the investigations of cationic species (salbutamol) by Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2003. Iontophoretic and chemical enhancement of drug delivery. Part I. Across artificial membranes. Int. J. Pharm. 12, 41-55. The method of vehicle preparation is also investigated. It is shown that ion pairing of the drug with the enhancer decreases the amount of drug available for transport from the liquid crystalline gels into aqueous receptor media. This decrease is directly related to the ratio of the concentration of drug to that of the enhancer. Buffering the vehicle inhibits the ion-pair formation to some extent. Vehicle preparation was also found to influence the degree of ion-pair association. The inclusion of a similarly charged enhancer (oleic acid) to the drug was found not to impede the diffusion of the drug from the gels.

Release characteristics of anionic drug compounds from liquid crystalline gels

Liquid crystalline gels (LCG) offer the formulator dynamic and flexible vehicles, into which actives, enhancers and other adjuvants with a wide range of physicochemical properties can be incorporated. This is achievable because of the biphasic oil/water composition of the gel. In this paper, the suitability of an isotropic liquid crystalline gel is investigated for a range of anionic drug molecules, with particular emphasis on sodium diclofenac. Parameters, which have been investigated, include the mode of vehicle preparation, the effect of the concentration of the drug and how buffering the gel and/or the receptor medium affect the release profiles. Such profiles have been measured for the sodium salts of benzoate, salicylate and indomethacin. The passive release from the standard system was found to adhere to matrix-controlled diffusion. An increase in concentration leads to a non-linear increase in the cumulative release of sodium diclofenac from the gels. In direct contrast to the result reported for cationic salbutamol base, optimum release from the gel was achieved when neither the receptor medium nor the aqueous phase of the gel was buffered. The percentages released of the sodium salts of benzoate, salicylate and indomethacin, after 24 h, were determined to be 25, 26 and 19%, respectively, and these are significantly greater than the release of sodium diclofenac. This suggests that diclofenac undergoes ion-pairing or complexation within the gel, which inhibits its diffusion from the vehicle. Future papers will report on the incorporation of enhancers and the effects of iontophoresis on the release profiles of drugs from these gels, and ultimately on the transdermal transport of drugs from these vehicles across human and porcine skin.