Tacrolimus-loaded nanostructured lipid carriers for oral delivery - Optimization of production and characterization

Tacrolimus (TL), which is currently the mainstay of immunosuppressive therapy faces significant hurdles subsequent to its oral administration attributable to its poor aqueous solubility and extensive intestinal and hepatic first pass metabolism. Therefore, the present study aimed to design the stable nanostructured lipid carrier (NLC) of TL that would be able to overcome such hurdles. Capmul MCMC8 and Compritol 888ATO in 3:2 were selected as binary lipid phase on the basis of solubility study. An exhaustive screening of surfactants is done by aqueous titration to select the surfactant with best emulsifying potential and to optimize the concentration of lipids and surfactants in NLC. Different methods of preparation were explored and compared to optimize NLC which could have the best characteristic properties. TL-NLC was characterized for particle size, drug entrapment efficiency, crystal state, surface morphology and drug release. The obtained particle size, PDI and % drug entrapment efficiency of optimized formulations i.e., NLC-C2 and NLC-N2 were 70±5.42nm, 98±7.52nm; 0.43±0.081, 0.2±0.029 and 87±2.34%, 94±3.18%, respectively. The results of in vitro release studies showed significantly increased (^***p<0.001) and sustained release of TL from NLC dispersions as compared to drug suspension (95.73% from NLC-C2, 99.86% from NLC-N2 and 9.27% drug suspension in pH 1.2 in 24h; 93.11% from NLC-C2, 96.65% from NLC-N2 and 10.2% drug suspension in pH 6.8 in 24h). The study demonstrated that proper selection of excipients (by aqueous titration) and modification of method of preparation (by inclusion of cold step) would lead to production of NLC with best characteristic properties.