Critical variables associated with nonbiodegradable osmotically controlled implants

Osmotically controlled implants yield precise zero-order drug delivery kinetics and are utilized in a number of applications. The implants deliver drugs for extended periods (weeks to years) and exhibit good in vivo/in vitro correlation. This paper reviews critical variables associated with these implants, with a focus on release rate testing. The extended-duration kinetics can be problematic when attempting to test for >70% cumulative delivery. An innovative scheme based on the scientific principles of operation of the system is described to ensure > 70% delivery at the target rate and duration for the DUROS Viadur (leuprolide acetate) implant.