Recent advances in the use of microspheres for targeted therapy

In recent years the concept of using small colloidal particles for the selective delivery of drugs has been explored experimentally using a variety of different physical systems (for example, phospholipid vesicles (liposomes), triglyceride emulsions, albumin microspheres) and routes of administration. In such studies the aim has been to target a potent pharmacological agent on an organ or tissue site, thereby reducing adverse reactions and side-effects, or to provide a means of controlled release. The design of appropriate delivery systems must take into account the nature of the target and physiological barriers to targeting as well as factors such as drug loading and drug release, stability of the carrier system and its biocompatibility and biodegradation. Targeting with microspheres can be divided into passive methods that rely upon physiological and physicochemical determinants such as entrapment in capillary beds (lungs - particle size) or uptake by phagocytic cells (liver-surface characteristics), an active method whereby the particle is directed to a specific site through the use of surface coatings (surfactants, glycolipids, monoclonal antibodies) or a material sensitive to an external influence. Candidate systems presently under study are described. These include lipid emulsions for intravenous administration and microspheres for intra-articular delivery.