The encapsulation of hydrophilic and lipophilic drugs by formulating them in SLNs results in their protection from degradation in the body and facilitates their prolonged release. Application of SLNs as a carrier system could be attributed to their unique features such as surface modification, enhanced permeation through biological membranes, increased resistance to chemical degradation, and ability to deliver two or more therapeutic agents.

Routes of Administration of SLNs

Oral Administration

SLNs may be administered orally after transformation into a traditional oral dosage form such as tablets, pellets, capsules, or powders. SLN dispersion can be used in place ofa granulation fluid during wet granulation processes. SLNs can be directly tableted if the dispersion is transformed to powder form by spray drying or lyophilization. Dry SLN powder may be filled into hard gelatin capsules, or SLNs may be directly produced in liquid polyethylene glycol 600 and filled into soft gelatin capsule. Also, SLNs may be directly commercialized as dry powders in sachet after spray drying or lyophilization since spray drying was found to be a more cost-effective method [5]. Various researchers have investigated SLNs for oral delivery of a variety of active compounds [54—58]. Cho et al. formulated SLNs incorporated with docetaxel, which has poor oral bioavailability [54]. SLNs were surface modified with tween 80 or D-alpha-tocopheryl poly(ethylene glycol 1000) succinate. The results indicated an increase in the oral bioavailability of docetaxel and thus SLNs may serve as an efficient oral drug delivery system for docetaxel [54]. SLNs of insulin were prepared using cetyl palmitate by Sarmento et al. and evaluated for oral delivery [55]. The SLNs were produced by a modified solvent emulsification—evaporation technique based on water/oil/water double emulsion. Oral administration of the formulated insulin- loaded SLNs to diabetic rats provided a considerable hypoglycemic effect during 24 h indicating SLNs to be a potential oral delivery system for insulin [55].

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