Iontophoretic Drug Delivery Systems Svetla Churchman, Mangala Patel, Alan Cruchley, Michael Braden, Gavin Pearson Introduction The aim of this project is to develop novel delivery vehicles for the iontophoretic delivery of high molecular weight agents across mucosal tissue. Preliminary experiments have been in progress to establish the experimental apparatus, with dextrans as the model molecules. FITC dextran (MWt 3kD) has been used, both to confer an electric charge to the dextran molecule, and to confer UV absorption at both 521 and 554nm. The diffusion cell utilises the classical "time lag" experiment. For initial experiments the input side had a dextran solution, and the diffusant was collected from the output side. Aliquots were removed at noted intervals, and analysed. The accelerating potential is applied via a KCl electrode in the input solution, an electrode in the output collection medium, and an iontophoresis power pack (Phoresor-850). Data was plotted as cumulative amount collected versus time, the key parameters being the time lag(t), the intercept of the linear region with the time axis, and the slope (s). For passive diffusion, tp = l2/6D 1) 2) s = ADC0/l where A is the area of the membrane, D the diffusion coefficient of the diffusing species, l the membrane thickness, and C0 the equilibrium concentration of the agent in the membrane tissue. In classical diffusion studies, this is a method of determining D and C0. In the case of Iontophoresis, the time lag is reduced to ti, where: ti = 3tp [coth (n/2)/(n/2)-1/(n/2)2] and si = spn/(1-e-n) where n = zFV/RT 3) 4) 5) where z is the accelerating potential, z the valency of the ion, F the Faraday Constant. Time-lag experiments using a potential of 1.5V is enabling these parameters to be investigated.
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