Solid Sirolimus Self-microemulsifying Drug Delivery System: Development and Evaluation of Tablets with Sustained Release Property

The clinical application of sirolimus (SRL) as an immunosuppressive agent is largely hampered by its narrow therapeutic range. This study focused on developing SRL tablets with a sustained release profile for better safety. SRL was highly water insoluble and its solubility has been efficiently enhanced by preparing self-microemulsifying drug delivery system (SMEDDS). The SRL-SMEDDS was physically adsorbed by microcrystalline cellulose (MCC). The sustained release of SRL was achieved by addition of hydroxypropyl methylcellulose (HPMC) to prepare tablets. The formulation of the tablets was optimized by single factor test and orthogonal design. The optimal formulation was composed of 10% of HPMC 1001v and 5% of HPMC K4M. The in-vitro release profiles of the optimal tablets were further investigated for the influence of hardness, shape, preparing method, release method, stirring speed, and medium. The release kinetic of SRL from the tablets was demonstrated to be erosion of HPMC. Pharmacokinetic study on beagle dogs showed that the SRL-SMEDDS tablets were bio-equivalent to the commercial tablets but lower C-max and larger T-max were achieved. In conclusion, the SMEDDS tablets were presented as promising delivery system for sustained release of SRL.