## 2 Dissolution and Stability Enhancement of Antimicrobial Compounds  
The formulation of poorly soluble and unstable drugs is a major challenge for pharmaceutical scientists. The poor water solubility of many antibiotics (Classes II and IV, according to the biopharmaceutical classification system) are associated with several serious problems, such as poor absorption, aggregation, or precipitation during the administration, which may reduce their bioavailability and produce undesirable side effects [12; 13]. In addition, the removal of antibiotics from the blood before reaching the infected tissue causes a prolonged exposure of bacteria to low levels of antibiotics, raising the risk for antibiotic resistance emergence. In this context, polymeric nanocarriers with unique physicochemical properties, especially a high surface-to-volume ratio, constitute a promising platform for overcoming these drug delivery limitations. By packaging the antimicrobials in a polymeric matrix, many nano-formulations have been used to increase efficacy and reduce adverse reactions by altering the physicochemical properties of the original drugs. For example, [PERSON] et al. described a guanidinylated dendrimeric vehicle for gaifloxacin, a zwitterionic antibiotic with a pH-dependent solubility profile [14]. The resulting dendrimer complex increased gaiffloxacin solubility by up to four fold and presented a greater rate of drug transport into the intraocular tissues during the short precorneal residence of drop formulation. In addition, the nano-formulation exhibited a 2 to 4 times faster killing rate in comparison to antibiotic solution against the resistant strain of methicillin-resistant _S. aureus_ (MRSA), which is commonly found in the conjunctiva. Likewise, [PERSON] et al. recently developed supramolecular hydrogel nano-antibiotics by conjugating small-molecule antibacterial triclosan to self-assembling peptides [15]. The resultant nano-antibiotics presented increased triclosan solubility by 850 fold. Furthermore, the nano-antibiotics smoothly accumulated at the bacterial infection site after intravenous injection and exhibited enhanced antibacterial activities with low side effects. Similarly, nano-encapsulation has also been applied to rescue various antimicrobials with disfavorable pharmacokinetic profiles such as ciprofloxacin [16], chloramphenicol [17], rochitromycin [18], essential oils [19; 20], and curcumin [21]. In addition to solubility limitations, poor stability may also limit the bioavailability of many drugs. Antimicrobial peptides (AMPs) have emerged in recent years as a promising substitute for conventional antibiotics. However, due to low stability in the ionic strength environment, efficient delivery of AMPs to their action sites remains a major obstacle, which significantly hampers their clinical application [22]. In this regard, polymeric nano-platforms may serve as a protective layer to antibiotics against environmental degradation, protect them from body clearance, and maintain sustainable therapeutic concentrations to achieve efficient treatments [23; 24]. For instance, in an attempt to overcome the peptide degradation by the harsh gut environment and ensure its bioavailability on oral administration, [PERSON] et al. developed an encapsulated system based on chitosan NPs for cryptdin-2 (a Paneth cell AMP) [24]. A developed nanocarrier system provided optimal stability of the active ingredient in gastrointestinal conditions and successful delivery of cryptdin-2 across the gut wall. In a mouse model of _Salmonella_ infection, the treatment of encapsulated peptide enhanced survival rates up to 83% versus 100% mortality observed with the free peptide. Alternatively, the inclusion of AMPs into polymeric NPs can also minimize undesirable interactions between their cationic residues with host cells, thereby reducing the required AMP dose and its systemic toxicity. For example, to reduce Colistin-induced nephrotoxicity and neurotoxicity, [PERSON] et al.