ABSTRACT
Early drug delivery methods typically involved simple oral administration as liquid, powder, or tablets or topical delivery. As drugs were developed, such as proteins and peptide drugs, which cannot overcome the natural barriers present in oral and topical delivery, they began to be injected or delivered intravenously. Recently developed drugs with narrow therapeutic concentrations, systemic side effects, short half lives, or other barriers to efficient application require advanced methods of delivery. Delivery of these compounds to a specific location (spatial control) or with a specific pattern (temporal control), or both, is being pursued to overcome these barriers. ‘‘Controlled release’’ refers to this type of delivery.
