Nanoparticulate drug carriers include a class of particles made of polymers or lipids that — because of their size and chemical composition —permit systemic and local treatment.
In general, these systems are expected to protect a drug from degradation, enhance drug absorption by facilitating diffusion through epithelium, modify the pharmacokinetic and drug tissue distribution profile and/or improve intracellular penetration and distribution.1–3
Although several liposomal formulations have been marketed since 1995 — illustrating that nanotechnology can be used to administer toxic drugs such as antifungal and anticancer agents — two new formulations for polymer nanoparticles entered clinical trials recently for cancer therapy.
This article focuses on the development of nanoparticulate drug carriers, highlighting several of the key issues being addressed up to now.
The design of nanoparticulate drug carriers must fulfil the following requirements:
As lipids are part of living constituents, they were considered to be suitable chemicals to formulate solid lipid nanoparticles (SLNs) and nanocapsules (LNCs) (Tables 1 and 2).
Synthetic polymers offer an almost infinite array of chemical composition and structure combinations. However, only a few have the requirements that make them useful as nanoparticulate drug carriers.
The prime candidates are polyesters including polylactide (PLA) derivatives and polyepsiloncaprolactone (PCL), polyalkylcyanoacrylate (PACA) and corresponding copolymers with polyethylene glycol (PEG), polysaccharides and polyethylenimine (Tables 1 and 2).
Natural macromolecules including polysaccharides (chitosan, alginate, pectine) were introduced to formulate hydrogel nanoparticles. Research is continuing to find suitable new polymers because polymers can be produced at lower cost than lipids and should be more interesting (economically) based on economic considerations.32 Polyesters of polymalic acid, polyamino acids of polybenzyl-glutamate) and pH- or temperature-sensitive species are growing in popularity.33–37