The effect of particle size on drug bioavailability in various parts of the body

Multiple mechanisms are involved in driving the efficacy of drug delivery. Drug particle size is one of the challenges as particles need to be delivered from the external environment, into the circulation or interstitial fluid and transiting the cell membranes for cellular internalisation. Small particles are presumably easier to be internalised, yet they are not easy to retain as they are subject to fast clearance. Big particles do not cross biological barriers as easily, but their size distribution is easier to be controlled. Because of the various routes of administration, the size range of these particles will also need to be catered for the anatomical, biological, and dynamic barriers involved. This review hopes to provide an insight into the range of particle size that has been engineered for drug delivery via various routes of administration of the body, such as to cross the epithelium of gastrointestinal tract, lungs, skin, blood-brain barrier, kidney and liver, the eye, nose, and ear, the cancer tumour matrix and into the muscles. While successful drug delivery also depends on the material properties of the delivery systems and the bio/nano interface related properties, this review focuses on the importance of particle size for enhancing bioavailability at the various organs of the body.