Enhanced Oral Bioavailability of Felodipine via Solid Self-microemulsion Delivery System

Felodipine (FEL), a first-line antihypertensive drug, suffers from low oral bioavailability due to its poor aqueous solubility and first-pass metabolism. This study aimed to enhance the oral bioavailability of FEL by developing a solid self-microemulsifying drug delivery system (FEL@S-SMEDDS). Initially, a pseudo-ternary phase diagram was constructed via the water titration method to identify the optimal oil phase, surfactant, and co-surfactant. The liquid SMEDDS (FEL@L-SMEDDS) was optimized using Response Surface Methodology (RSM), resulting in a composition of 8.91% FEL (drug loading), 22.77% ethyl oleate, 47.30% EL 35, and 21.02% Transcutol HP. The FEL@L-SMEDDS exhibited a spherical-like morphology with an average particle size of 27.80 nm, a PDI of 0.074, a zeta potential of -3.44 mV, an emulsification time of 34 s, and a transmittance of 96.1%. Following the establishment of this optimized liquid system, FEL@L-SMEDDS was solidified using Neusilin® US2 at a liquid-to-solid mass ratio of 1.5:1 to obtain FEL@S-SMEDDS, which was comprehensively characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). In terms of stability, FEL@S-SMEDDS exhibited excellent performance under accelerated conditions (40 ± 2℃, 75 ± 5% relative humidity) for 6 months. Regarding in vitro release behavior, FEL@S-SMEDDS afforded over 90% drug release within 30 min across different dissolution media, exhibiting a pH-independent release profile. Ultimately, the efficacy of this formulation was validated through pharmacokinetic evaluations in rats, revealing that the peak drug concentration (C max ) and area under the drug concentration–time curve (AUC 0-24 h ) of FEL@S-SMEDDS were increased by 2.73-fold and 1.46-fold higher than those of commercial FEL tablet, respectively. In conclusion, FEL@S-SMEDDS represents a promising strategy for enhancing the oral bioavailability and therapeutic efficacy of FEL in hypertension management.