The primary indication of sildenafil is the treatment of erectile dysfunction. It is also effective in pulmonary arterial hypertension; its absolute bioavailability is 41% due to first-pass metabolism. In this work; attempt was made to prepare sildenafil solid lipid nanoparticles suitable for nebulization for direct application into the lung to increase bioavailability, and increase its local action on the pulmonary arteries. Solid lipid nanoparticles were prepared by hot homogenization- ultrasonication technique using Precirol ATO 5, Compritol 888 and Glyceryl monostearate as solid lipids. Gelucire 44/14, Pluronic f68 and Cremophor EL as surfactants. The prepared SLNs were evaluated by measuring particle size, zeta potential, and drug loading capacity. The drug release rate at simulated lung conditions were examined. The optimized SLN formula was further examined for particle shape using SEM and solid state characterization by DSC, IR and XRD. Results showed that the prepared SLN formulae had particle size in the range of 44 to 107 nm, with percentage drug of 94.39% to 89.11% and +20.3 to + 24.5 mV zeta-potential. The drug release from prepared SLN was improved with a slow prolonged rate, where percentage drug released exceeded 75 up to 95.12% from different SLN formulations within 12 hours in comparison to 26.83 % for plain drug. For the optimized formula, The drug melting peak at 189.88ºC on DSC thermogram was completely disappeared, drug main functional groups were all retained in IR spectrum while XRD pattern showed disappearance of drug characteristic peaks. SEM results showed that the prepared particles were spherical with irregular surface. Depending on these results it could be concluded that SLN formula is efficient dosage form suitable for nebulization and delivery through the lung due to small particle size, uniform size distribution, high drug tolerating ability, compatibility and ability to improve drug release rate over extended time period.
