ncrease in drug therapeutic efficacy and reduction in side effects [54]; (3) site-specific targeting can be achieved by attaching targeting ligands to surface of particles or use of magnetic guidance [55, 56]; (4) controlled release and particle degradation characteristics can be readily modulated by the choice of matrix constituents. Due to biodegradability, pH, ion and/or temperature sensibility of materials they allow sustained drug release within the target site over a period of days or weeks [40, 57]; (5) they can pass through smallest capillary vessels and be taken up by cells, which allow efficient drug accumulation at the target sites [58-60] because of their ultra-tiny volume and avoiding rapid clearance by phagocytes so their duration in blood stream is deeply prolonged. This is especially needed for tumors which are characterized by extensive angiogenesis, defective vascular architecture, impaired lymphatic drainage and increased production of permeability factors. This phenomenon is known as the enhanced permeability and retention effect [13, 57, 61]; (6) increased active agent surface area results in a faster dissolution of the active agent in an aqueous environment, such as the human body. Faster dissolution generally equates with greater bioavailability, smaller drug doses, less toxicity[62]. (7) Can be used for different routes of administration, including oral, nasal, intra-ocular and surface characteristics can be simply manipulated to achieve both passive and active drug targeting after parenteral administration and (8) reduction in fed/fasted variability (9) due to the impressive bioavailability, better encapsulation, control release and less toxic properties, various nanoparticle systems with biodegradable polymers such as PLGA, PLA, chitosan and gelatin are utilized for delivery of drugs of various types of diseases with better efficacy [63]. (10) In recent years oral bioavailability of many of poorly water soluble drugs can be modified by incorporating drugs into pH sensitive nanoparticles . (11) Nanoparticles are now used to study the expression of therapeutic genes, is a useful tool for gene therapy.

Pharmaceutical nanocarriers, that are designated as NPDDS, can be classi