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Long acting injections and implants emerged as a sub-area of pharmaceutics in the twentieth century, with companies dedicated to the fi eld being established in the 1960s and 1970s. The fi eld contains a wide range of system types. This chapter summarizes the historical development of the fi eld, including rate-controlled membrane concepts, biodegradable polymer concepts, surface-releasing systems, liposomes, targeted/nanoscale systems, and microelectronic systems.

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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.