Solid lipid nanoparticles (SLNs) are primarily composed of solid lipids, which thus impart to them some of the fundamental
properties of these lipids, including biocompatibility, biodegradability and low-toxicity. SLNs represent a unique class of colloidal drug
delivery systems that possess the advantages of both the “soft” drug carriers such as emulsions and liposomes and polymeric nanoparticles.
In this review, we will provide an overview on the absorption, disposition and pharmacokinetics of SLNs. The lipidic nature, as well
as the relatively small particle size, of SLNs ensures sufficient affinity with the biomembranes, and results in improved absorption by either
of the oral, transdermal, pulmonary, nasal, ocular, rectal or buccal route. One special aspect of oral SLNs is the enhanced lymphatic
absorption by either the chylomicron-association pathway or the M cell uptaking pathway. Intravenous SLNs are predominantly uptaken
by the liver or spleen following opsonization by the complementary system. Modification of SLN surface with PEGs chains will mask
the hydrophobic surface and divert SLNs to non-hepatic and non-splenic organs, while ligand-modification will achieve active targeting
to specific tissues or organs. Degradation of SLNs is primarily based on the degradation of the lipids themselves by lipase. Pharmacokinetics
reflects the effect of the lipidic vehicles of SLNs on in vivo disposition of the loaded drugs.