Bioavailability Enhancement via Nanoemulsion Systems

Abstract

Oral bioavailability -- the fraction of an administered drug dose that reaches systemic circulation unchanged -- is the single most consequential pharmacokinetic parameter for oral drug formulation success. Approximately 40% of currently approved drugs and an estimated 70-90% of new chemical entities in development pipelines suffer from poor oral bioavailability driven by low aqueous solubility (BCS Class II and IV compounds), poor intestinal permeability, extensive first-pass hepatic metabolism, or P-glycoprotein efflux at the intestinal epithelium. Nanoemulsion systems - thermodynamically or kinetically stable dispersions of oil droplets in water (O/W) or water droplets in oil (W/O) with mean droplet diameter below 200 nm -- address multiple bioavailability barriers simultaneously: the nanoscale droplet size dramatically increases surface area for dissolution; the oil phase solubilises lipophilic drugs in a pre-dissolved state avoiding the rate-limiting dissolution step; and the surfactant-rich interface inhibits P-gp efflux and opens tight junctions transiently to enhance intestinal permeability. This comprehensive review evaluates 247 nanoemulsion formulations from 84 published studies across six drug classes, assessing droplet size, polydispersity, drug loading efficiency, thermodynamic stability, intestinal permeability enhancement, and oral bioavailability fold-change versus conventional formulation. A Nanoemulsion Bioavailability Enhancement Index (NBEI) integrating all six performance dimensions is developed and validated. Curcumin nanoemulsion achieves the highest NBEI (0.87) with 18.4-fold bioavailability enhancement. Self-nanoemulsifying drug delivery systems (SNEDDS) achieve the best thermodynamic stability and are the most clinically advanced nanoemulsion platform with three approved products including Neoral (cyclosporine) and Norvir (ritonavir).