Journal of Controlled Release 60 (1999) 355–365 Gelatin-stabilised microemulsion-based organogels: rheology and application in iontophoretic transdermal drug delivery 1 * Shilpa Kantaria, Gareth D. Rees , M. Jayne Lawrence Department of Pharmacy, King’ s College London, Manresa Road, Chelsea SW36LX, London, UK Received 12 November 1998; received in revised form 20 March 1999; accepted 31 March 1999 Abstract Gelatin-containing microemulsion-based organogels (MBGs) have been formulated using pharmaceutically acceptable surfactants and oils such as Tween 85 and isopropyl myristate. MBG formulations were subject to rheological study and their utility in transdermal drug delivery examined. Unlike most organogels, MBGs are electrically conducting and have been successfully employed in this study for the iontophoretic delivery of a model drug through excised pig skin. Iontophoresis using MBGs gave substantially higher release rates for sodium salicylate compared to passive diffusion, and fluxes were proportional to the drug loading and the current density. MBGs provide a convenient means of immobilising the drug and are rheologically similar to their hydrogel counterparts at comparable gelatin concentrations. MBGs also appear to offer improved microbial resistance in comparison to aqueous solution or hydrogels.  1999 Elsevier Science B.V. All rights reserved. Keywords: Microemulsion-based gel; Transdermal drug delivery; Rheology; Iontophoresis 1. Introduction drug reservoir is formulated as a solution since this can limit the ease of clinical administration. The Iontophoresis has been used extensively in recent development of more convenient reservoir systems is years as a means of enhancing the rate of transder- clearly desirable and one notable area of interest has mal drug delivery [1–3], and is particularly effective been the use of drug-containing hydrogels. Formula- in facilitating transport of larger hydrophilic species tion of the drug as a gel rather than a solution such as peptides, proteins and nucleotides which facilitates drug handling and in the case of ion- often exhibit negligible penetration under passive tophoretic delivery, allows the patient to remain conditions. A potential practical drawback of drug ambulant. delivery via iontophoresis, however, occurs when the There has been considerable interest generally in the development of ‘intelligent’ or responsive hydro- gels which react to a variety of environmental stimuli *Corresponding author. Tel.: 144-171-333-4808; fax: 144- such as pH, temperature or the presence of a 171-351-5307. particular substrate [4]. For iontophoretic application, E-mail address: jayne.lawrence@kcl.ac.uk (M.J. Lawrence) 1 particular benefit would accrue from the use of Present address: SmithKline Beecham, Research & Develop- ment, St. George’s Avenue, Weybridge, Surrey KT13 0DE, UK. electro-responsive hydrogels where the aim is to 0168-3659 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0168-3659(99)00092-9