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The dissolution rate and the oral bioavailability of nitrendipine were significantly affected by the crystal size, and the oral bioavailability could be improved significantly by preparing it as nanocrystals. FaSSIF can be used to predict differences in oral absorption of crystals with different particle sizes.

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S.O (sodium oleate) is an anionic surfactant, which is able to forman ionic complex with positively charged insulin at suitable pH. In a previous study, the insulin-S.O (Ins-S.O) complex was prepared by a hydrophobic ion pairing (HIP) method to improve the apparent liposolubility of insulin. The formation of the complex was further confirmed by Zeta potential and X-ray method. Based on the preliminary study, poly(lactide-co-glycolide) (PLGA) nanoparticles harbouring Ins-S.O complex was prepared via an emulsion solvent diffusion method. The effects of key parameters such as concentration of PVA, concentration of PLGA and initial-loaded drug on the properties of the nanoparticles were investigated. The insulin encapsulation efficiency (EE(%)) reached up to 91.2% and mean diameter of the nanoparticles was sized approximately 160 nm under optimal conditions. The pharmacological effects of the nanoparticles made of PLGA (75/25, Av Mw 15,000) were further evaluated to confirm their potential suitability for oral delivery. In order to evaluate hyperglycaemic effect of the nanoparticles for oral administration, Ins-S.O complex-loaded PLGA nanoparticles (20 IU/Kg) were administered orally by force-feeding to diabetic rats. In the case of the nanoparticles, the plasma glucose level reduced to 23.85% from the initial one 12 h post-administration and this continued for 24 h. The results showed that the use of Ins-S.O complex-loaded PLGA nanoparticles is an effective method of reducing plasma glucose levels. The insulin nanoparticles also improved the glycaemic response to an oral glucose challenge.

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