Reverse iontophoretic monitoring in premature neonates: feasibility and potential

Premature neonates represent a fragile patient population, often subjected to intensive clinical care and multiple drug therapy, which must be monitored carefully and continuously. The difficult and painful nature of repetitive blood sampling, particularly in this population, has provided considerable impetus for the development of noninvasive methods for monitoring blood analytes. Reverse iontophoresis, a relatively new technology already used for the transdermal monitoring of blood glucose levels in adults, may be particularly well-suited to exploit the unique properties of preterm neonatal skin. The underdevelopment of the premature infant's epidermis, and more specifically the stratum corneum (SC), results in an increased permeability to molecular transport. In this study, we have investigated the feasibility of reverse iontophoretic monitoring of two model drugs, caffeine and theophylline, which are often administered to premature neonates. To this purpose, tape-stripped porcine skin in vitro, which has been previously demonstrated to be an excellent model for premature neonatal skin, was employed. Reverse iontophoresis across intact membranes enabled a quantifiable extraction of both drugs predominantly at the cathode compartment. The mechanism of extraction of these essentially neutral drugs (caffeine and theophylline being uncharged at pH 7.4) was electroosmosis. However, when the SC was removed by progressive tape-stripping, the amounts of drugs extracted by reverse iontophoresis were equivalent to those obtained by passive diffusion. In these circumstances, therefore, the benefit and usefulness of the applied electric field had been lost. In summary, the absence of an at least partially functional skin barrier obviates, in the case of neutral molecules, the control (and directional transport) offered by iontophoresis; in contrast, for ionized species, where the principal iontophoretic transport mechanism is electromigration, the approach should be valid.