Liposomes in the treatment of infectious diseases

Phospholipids and other polar lipids can form liposomes and similar colloidal particles that can be used as drug carrier systems. The potential of liposomal delivery systems to increase the therapeutic index (efficacy to safety ratio) of clinically important drugs has been realised with the recent approval of liposomal oncologic and antifungal drugs. The application of liposomes to the treatment of infectious diseases initially focused on intracellular pathogens, based on the natural targeting of liposomes to phagocytic cells and on the antifungal drug amphotericin B, based on its unique affinity for lipids. Recent studies with small, low-clearance liposomes have shown that more specialised formulations may provide benefits over simpler 'first generation' liposomes for the treatment of infectious diseases, including prolonged residence in plasma, increased tissue exposure and targeting to sites of infection. These improved biopharmaceutical properties have been associated with both curative and prophylactic activity against a range of non-intracellular pathogens, including Staphylococcus and Klebsiella. These and other highly engineered liposome formulations may provide effective delivery systems for specific antibacterial, antifungal and antiviral indications in the future. Adequate patent protection will be crucial in fully exploiting these advanced liposome technologies and in maintaining market share for liposomal products. This review discusses some of the patent issues related to liposomes and their use in the treatment of infectious diseases.