However, they should have high encapsulation efficiency with sustained and prolonged intracellular antibiotic release. For example, our core–shell nanostructures can incorporate up to 25% by weight of gentamicin, and about 25–30% of the gentamicin is released over 24 h in phosphate buffer saline at pH 7.4 (Ranjan et al., 2010a ,b). But, as the gentamicin begins to leave the complex, the net anionic character of the complexes increases. As this occurs, greater electrostatic attraction between the polymer and gentamicin slows or

completely prevent further release. Therefore, nanocarrier needs to be modified such that they degrade slowly to release 100% of the encapsulate drug. We recently reported

biodegradable silica xerogel nanocarrier for complete drug release (Seleem et al., 2009a ,b). Xerogel nanostructures are prepared by a sol–gel process. This involves formation A-769662 in vivo of a colloidal suspension (sol) that acts as a precursor for globally connected integrated solid matrix (gel) that can be dried to form xerogel (Quintanar-Guerrero et al., 2009). The xerogels can be fabricated and tuned at low temperatures to carry biologically active agents like gentamicin (Xue et al., 2006). Silica xerogels nanostructures prepared by our technique can incorporate 17% gentamicin by weight and releases 90% of gentamicin in 30 h in vitro. Gentamicin release from these nanostructures Mitomycin C nmr is biphasic. A total of 20–25% of drug is initially released at a burst rate followed by a slower and steady state. Biphasic release may be problematic in vivo because burst release can result in encapsulated

drug acting similar to its free form. This is reflected all in an incomplete in vivo clearance of intracellular Salmonella in the livers (1.15 log reduction in CFU) and spleen (0.41 log reduction in CFU). Therefore, although the results are encouraging, careful engineering and chemical principles are required in particle synthesis to address these issues before further clinical application. This review summarized the recent findings on targeting of intracellular pathogens especially Salmonella. As discussed, incorporation of antimicrobials in a nanocarrier provides a novel method for intracellular drug delivery and enhancing their killing effect. However, complete eradication of intracellular pathogens using this methodology is yet to be realized. Targeted drug delivery and their intracellular bioactivity are two separate issues. In our opinion, antibacterial nanomedicine in its true sense is the delivery of targeted drug to the subcellular niche where a bacterium resides. Currently available technologies deliver drugs to the cell endosome or cytoplasm and hence may not be fully targeted. Endosomal or cytoplasmic delivery exposes drug initially to the cellular microenvironment prior to their interaction with the bacteria.