Solid lipid nanoparticles and nanosuspension of adefovir dipivoxil for bioavailability improvement: formulation, characterization, pharmacokinetic and biodistribution studies

The present study was aimed at developing colloidal formulations like solid lipid nanoparticles (SLN) and nanosuspension (NS) for improving bioavailability of adefovir dipivoxil (AD), a nucleoside reverse transcriptase inhibitor which displays poor oral bioavailability. SLNs were prepared by solvent injection method while NS was prepared by pearl milling method. The prepared formulations were characterized for physicochemical parameters such as particle size,. potential, drug content, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC). Pharmacokinetic and biodistribution studies were performed in mice to evaluate in vivo fate of the formulations. The SLNs showed particle size of 267 +/- 18 nm and entrapment efficiency of 73.5 +/- 2.12%. The particle size obtained for NS was 393 +/- 13 nm against 710 +/- 70 mu m for bulk drug, which led to significant improvement in saturation solubility. DSC and XRD studies of NS and SLN showed reduction in crystallinity while in vitro studies showed improved dissolution rate in both cases. Pharmacokinetics studies of orally administered formulations in mice exhibited higher plasma concentration compared to plain drug. Biodistribution studies showed higher accumulation of drug in liver, kidneys, intestine and stomach. The higher concentration of AD in liver after 24 hr highlights its potential advantage for effective treatment of chronic hepatitis infection. The relative bioavailability for adefovir NS and SLN were 52.46% and 78.23% respectively compared to 34.34% bioavailability obtained after administration of adefovir micro suspension (AMS), indicating suitability of both nanoparticulate formulations for improving bioavailability. SLNs were found to performed better as compared to NS for improving the bioavailability of AD.