Griffin [88] defined the lipophilic emulsifiers as low HLB values (below 9), and hydrophilic emulsifiers as high HLB values (above 11). Those in the range of 9–11 are intermediate [89]. The HLB system is a useful method to choose the ideal emulsifier or blend of emulsifiers for the system, that is, if its required an oil-in-water (o/w), water-in-oil (w/o) [90], or a double (w/o/w) emulsion. Matching the HLB value of the surfactant with the lipid will provide a suitable in vitro performance [91]. Table Inhibitors,research,lifescience,medical 3 depicts the mainly surfactants employed in the production

of lipid nanoparticles. Table 3 Emulsifiers used for the production of lipid nanoparticles. Severino et al. Inhibitors,research,lifescience,medical [10] determined the HLB value for stearic acid and stearic acid capric/caprylic triglycerides to reach the best

combination of surfactants (trioleate sorbitan and polysorbate 80) to obtain a stable lipid nanoparticles emulsion. The HLB value obtained for stearic acid was 15 and for stearic acid capric/caprylic triglycerides was 13.8. Sorbitan trioleate has an HLB value of 1.8 and polysorbate 80 of 15, when used in the ratio 10:90, respectively. The surfactant mixtures prepared with different ratios provided well-defined HLB values. Polysorbate 80 is often used in combination Inhibitors,research,lifescience,medical with sorbitan trioleate due to their appropriate compatibility attributed to the similar chemical structure (same hydrocarbon chain length) for the production of stable emulsions. 4. Biopharmaceutic and Pharmacokinetic Aspects Pharmacokinetic Inhibitors,research,lifescience,medical behaviour of drugs loaded in lipid nanoparticles

need to differentiate if the drug is present as the released free form or as the associated form with lipid nanoparticles [106]. However, the poor aqueous solubility of some drugs turns difficult the design of pharmaceutical formulations and leads to variable bioavailability [107]. Xie et al. [108] reported a significant increase in the bioavailability and extended the systemic circulation of ofloxacin formulated in SLN, which could be attributed Inhibitors,research,lifescience,medical to a large surface area of the particles, improving the dissolution rate and level of ofloxacin in the presence of GIT fluids [109, 110], leading to shorter Tmax and higher peak plasma concentration. and In addition, lipid nanoparticles may adhere to the GIT wall or enter the intervillar spaces due to their small particle size, increasing their residence time [111]. Moreover, nanoparticles could protect the drug from chemical and enzymatic PD0332991 degradation and gradually release drug from the lipid matrix into blood, [112] resulting in a several-fold increase mean residence time compared with native drug. Han et al. [113] demonstrated that 5 oral doses of tilmicosin loaded in lipid nanoparticles administered every 10 days provided an equivalent therapeutic benefit to 46 daily doses of oral free drugs.