Nanostructures and nanoparticles can be used for drug delivery purposes, either as the drug formulation itself or as the drug delivery carrier (Cascone et al 2002, Baran et al 2002, Duncan 2003, Kipp 2004). Current research focuses on cancer therapy, diagnostics and imaging, although many challenges still need to be solved (Ferrari 2005). In addition, nanostructures are being investigated for gene delivery purposes (Kneuer et al 2000, Salem et al 2003, Ravi Kumar et al 2004, Gemeinhart et al 2005, Yoo et al 2005, Roy et al 2005).
Many different formulations involving nanoparticles have been used for drug delivery purposes, including albumin (Damascelli et al 2003), poly(D,L-lactic-co-glycolide)acid (PLGA) (Panyam et al 2002, Weissenbock et al 2004), solid lipid formulations (Muller et al 1997, 2000, Wissing et al 2004), cetyl alcohol/polysorbate nanoparticles (Koziara et al 2004), hydrogels (Gupta and Gupta 2004), gold (Hainfeld et al 2004, Paciotti et al 2004), polyalkylcyanoacrylate composites (Cruz et al 1997, Olivier et al 1999, Kreuter et al 2003), magnetic iron oxide (Gupta and Gupta 2005), methoxy poly(ethylene glycol)/poly(ε-caprolactone) (Kim et al 2003), and gelatin (Cascone et al 2002). Albumin nanoparticles are already the subject of clinical studies for anticancer drug delivery purposes (Damascelli et al 2003).
Not all of the ‘nanoparticle formulations’ mentioned are strictly or solely nanoparticulate in the sense that their size is not always below 100 nm and some drug delivery systems include particles up to several hundreds of nanometres. In many cases, the technology to produce very small particles did not exist in the early stages of development, but now there is an increasing refinement in their size and it is relevant to this Opinion to discuss this group of products together. The route of administration may be oral, parental (subcutaneous, intramuscular, intra-arterial, intravenous) and via the skin.