Darunavir, an anti-HIV drug having poor solubility in aqueous and lipid medium, illustrates degradation above its melting point, i.e. 74°C, thus, posing a challenge to dosage formulation. Despite, the drug suffers from poor oral bioavailability (37%) owing to less permeability and being poly-glycoprotein and cyp3A metabolism substrate. The study aimed formulating a SLN system to overcome the formulation and bioavailability associated problems of the drug. Based on the drug solubility and stable dispersion findings, lipid and surfactant were chosen and nanoparticles were prepared using hot-homogenization technique. Optimization of variables such as lipid concentration, oilsurfactant and homogenization cycle was carried and their effect on particle size and entrapment efficiency was studied. Freeze-dried SLN further characterized using SEM, DSC and PXRD analysis revealed complete entrapment of the drug and amorphous nature of the SLN. In vitro pH release studies in 0.1 N HCl and 6.8 pH buffer demonstrated 84 and 80% release at the end of 12th h. The apparent permeability of the SLN across rat intestine was found to be 24 9 10-6 at 37°C at the end of 30 min while at 4°C the same was found to be 5.6 9 10-6 prompting involvement of endocytic processes in the uptake of SLN. Accelerated stability studies revealed no prominent changes upon storage.

Darunavir is effective against wild-type and PI-resistant HIV, and has an oral bioavailability of 37%. It needs to be combined with ritonavir, which increases the bioavailability to 82%. The aim of this study was to evaluate the in-vivo efficacy of the darunavir-SLN and demonstrate lymphatic transport as a contributing pathway in increasing the drug bioavailability. The SLN was prepared by hot-homogenization technique using GMS as lipid. In-vitro drug release from SLN at the 12th hour was retarded (80.6%) compared to marketed tablet (92.6%). Ex-vivo apparent permeability of the freeze-dried SLN across everted rat intestine was 24 × 10 at 37 °C and 5.6 × 10 at 4 °C. The presence of endocytic process inhibitors like chlorpromazine and nystatin reduced it to 18.8 × 10 and 20.2 × 10, respectively, which established involvement of endocytic mechanism in the uptake of SLN. In-vivo pharmacokinetic studies on rats demonstrated increase in the AUC of SLN (26) as compared to that of marketed tablet (13.22), while the presence of lymphatic uptake inhibitor cycloheximide lowered the AUC of SLN to 17.19 which further led credence to the involvement of lymphatic uptake behind improved bioavailability. The detection of darunavir in the lymphatic fluid of the rats administered with darunavir-SLN further reinforced the conclusion of SLN being taken up by the lymphatic system.

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