Lipid implants as drug delivery systems

The parenteral controlled delivery of acid-labile drugs (e.g., proteins) is difficult, because the standard polymer poly(lactic-co-glycolic acid) used to control drug release upon parenteral administration degrades into shorter chain acids, creating acidic microclimates. Lipid implants do not show this disadvantage. The objective of this article is to give an overview on the present state of the art and to highlight the advantages and drawbacks of the different types of systems reported in the literature. The major preparation techniques for lipid implants, underlying mass transport mechanisms, biocompatibility and in vivo performance of the most interesting systems are described. Lipid implants offer a great potential as parenteral controlled drug delivery systems, especially for protein-based drugs. A broad spectra of release patterns can be provided and acidic microclimates avoided.