Abstract
The poor solubility and permeability of Biopharmaceutics Classification System (BCS) Class IV drugs pose major challenges to achieving sufficient oral bioavailability and therapeutic efficacy. Improving drug dissolution is a key strategy to enhance bioavailability, which in turn can enable more effective targeting of drugs to their site of action. To address this, we formulated cefdinir, a model BCS Class IV compound, using three amorphisation strategies; solid dispersions, mesoporous silica dispersions, and co-amorphous systems to assess the impact of formulation on stability and dissolution. Formulations were prepared via spray drying and solvent immersion using different drug-to-polymer ratios, with miscibility predicted using Flory-Huggins theory. The amorphous nature of each system was confirmed using differential scanning calorimetry (DSC), polarised light microscopy (PLM), and powder X-ray diffraction (PXRD). Dissolution studies revealed significantly enhanced drug release from all formulations compared to crystalline cefdinir. Among them, solid dispersion and co-amorphous systems exhibited the greatest improvement in dissolution rates, attributed to their ability to maintain supersaturation and inhibit crystallisation via kinetic stabilisation. These systems also showed better physical stability under non-sink aqueous conditions. However, mesoporous silica dispersions demonstrated superior long-term stability, retaining over 95% drug content and preserving their amorphous structure across three storage conditions (25 °C/0% RH, 40 °C/0% RH, and 40 °C/75% RH) for 6 months. This was attributed to the confinement of the drug within silica pores and the absence of hygroscopic excipients. Overall, this study highlights the distinct advantages of each approach, emphasising the importance of balancing dissolution enhancement with solid-state stability, and supports the use of theoretical modelling to guide rational formulation design for poorly soluble drugs to improve oral bioavailability and enable more targeted therapeutic outcomes.