Advances in lipid nanodispersions for parenteral drug delivery and targeting

Parenteral formulations, particularly intravascular ones, offer a unique opportunity for direct access to the bloodstream and rapid onset of drug action as well as targeting to specific organ and tissue sites. Triglyceride emulsions, liposomes and micellar solutions have been traditionally used to accomplish these tasks and there are several products on the market using these lipid formulations. The broader application of these lipid systems in parenteral drug delivery, however, particularly with new chemical entities, has been limited due primarily to the following reasons: a) only a small number of parenteral lipid excipients are approved, b) there is increasing number of drugs that are partially or not soluble in conventional oils and other lipid solvents, and c) the ongoing requirement for site-specific targeting and controlled drug release. Thus, there is growing need to expand the array of targetable lipid-based systems to deliver a wide variety of drugs and produce stable formulations which can be easily manufactured in a sterile form, are cost-effective and at least as safe and efficacious as the earlier developed systems. These advanced parenteral lipid-based systems are at various stages of preclinical and clinical development which include nanoemulsions, nanosuspensions and polymeric phospholipid micelles. This review article will showcase these parenteral lipid nanosystems and discuss advances in relation to formulation development, processing and manufacturing, and stability assessment. Factors controlling drug encapsulation and release and in vivo biodistribution will be emphasized along with in vitro/in vivo toxicity and efficacy case studies. Emerging lipid excipients and increasing applications of injectable lipid nanocarriers in cancer chemotherapy and other disease indications will be highlighted and in vitro/in vivo case studies will be presented. As these new parenteral lipid systems advance through the clinic and product launch, their therapeutic utility and value will certainly expand.