Assessment of the Time Required for Controlled-Release Devices to Reach Steady State
Laurent Simon, Otto H. York Department of Chemical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102
Assessing whether a desired release rate will be achieved in a certain period of time is a challenge that transdermal patch manufacturers must address. An engineering-based design methodology is suggested in this contribution to respond to patient need for a more accurate and timely release of active pharmaceutical ingredient(s) to the target site. New design equations, based on principles of transport phenomena, are derived to facilitate the rapid development of controlled-release devices. Concepts, such as an effective time constant, traditionally used to analyze dynamical systems, are invoked to estimate the time it takes to reach a steady-state flux in passive and physically-enhanced delivery systems. Three case studies were investigated to illustrate the methodology: benzocaine transport through ethylene-vinyl acetate membranes, iontophoretic delivery of amitriptyline HCl across human skin and heat-enhanced transport of desoxycorticosterone through silicone membranes. The predictions agree with drug-release profiles.