| Summary: | Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. Pharmacy Bibliography: leaves 107-127. Introduction: Transdermal electroporation involves the application of high voltage electrical pulses for microsecond to millisecond duration to produce reversible increase in permeability of skin. It can provide an alternative route to intravenous injection for the fast delivery of macromolecules molecules such as proteins and peptide drugs in clinically effective amounts for the patient. However, the mechanism of electroporation and its safety are unclear. Hence, electrical parameters for delivery of individual drugs have to be chosen empirically or by careful optimization. -- Objectives: To carry out optimization of electrical parameters using fuzzy rat skin tissue in vitro for delivery of terazosin hydrochloride (TRZ), followed by use of these parameters in live fuzzy rats (in vivo), to study their safety and effectiveness. To design in vitro and in vivo tests to predict the safety of this technique. Materials: Side-by-side diffusion cells were used for in vitro and in vivo studies. Ag/AgCI electrodes of different areas were used to deliver the exponentially decaying electroporation pulses from a Gene Pulser® (BioRad Laboratories, USA). Fuzzy rats and freshly excised full thickness skin from fuzzy rats were used for in vivo and in vitro studies respectively. -- Methods: Pulse length and rate of pulsing were evaluated with respect to their ability to reverse the increased permeability caused by electroporation. The correlation between TRZ concentration and increase in electroporative delivery was studied. Based on above studies optimal parameters were chosen to deliver TRZ in vivo. Their safety and effectiveness were compared to delivery without electroporation (control). Pharmacokinetic parameters were estimated by giving drug intravenously and subcutaneously. In vivo impedance recovery of skin after electroporation to pre-electroporated state was studied to predict safety. Similarly, uptake of glucose by skin with or without electroporation was studied to predict change in viability (damage) in vitro. Finally, electrodes of different area were characterized in vitro with respect to the electrical parameters. These parameters in conjunction with the in vitro and in vivo drug delivery and safety studies would throw some light on the mechanism of electroporation and the effect of electrode area on drug delivery and safety by electroporation. -- Results and discussion: If electroporation is completely reversible then the rate of transport of drug through the skin after stopping electroporation pulses should be the same as that through non-pulsed skin. Using this method an applied voltage (Ueiectrode.o) of 400V, a pulse length of 20 millisecond and a rate of pulsing of 10 pulse per minute (ppm) were found to be relatively safe and delivered significantly higher drug compared to passive drug delivery. Increased donor concentration gave higher delivery and may help in reducing exposure to higher electrical conditions to produce same amount of drug delivery. In vivo studies showed that TRZ can be delivered safely and effectively with electroporation. However, the effect of electrode area needs to be studied further. Pharmacokinetic studies indicated depot formation within skin after electroporation and this could be due to limited blood flow to the skin. In vitro biochemical studies showed a lag time in lactate production when a very high voltage electroporation pulse was used and there was a general stimulation of lactate production (as a result of glucose utilization) after electroporation compared to non-electroporated skin. The lag time may be used to predict damage due to electroporation. In vitro electrode characterization studies gave considerable insight into the observed drug delivery profiles and the differences in safety profiles between the different electrodes. In vivo impedance studies showed that complete recovery of skin impedance after electroporation might take hours to days. Recovery was faster with shorter pulse lengths and lower number of pulses. -- Conclusions: An applied voltage of 400 V, 20 pulses of 20 millisecond at the rate of 10 pulses per minute with 10% TRZ in contact with skin and using a small area electrode was found to be relatively safe and effective for delivery of TRZ in vitro and in vivo, with higher delivery for higher electrode area as predicted. The in vitro electrode characterization experiments could explain some of the observed differences between the drug delivery by different electrodes and in vitro viability studies could predict damaging electrical conditions. In vivo impedance studies showed that the parameters which can cause appreciable recovery of impedance after electroporation, are those that have not shown to deliver appreciable amount of drug in vitro, at least by electroporation alone. New electrode designs or new methods will have to be devised to increase safety of electroporation before electroporation can be considered useful or tested on humans.
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