Enteric Coating Enhances the Biopharmaceutical Performance of a Silica-Lipid Formulation of Abiraterone Acetate

Background/Objectives: Lipid-based formulations are widely used to enhance the oral bioavailability of poorly water-soluble drugs. However, for weakly basic drugs with higher solubility under acidic conditions, precipitation and recrystallisation after gastric emptying can compromise a formulation's ability to maintain the drug in a solubilised, absorbable state. To address this, we evaluated an enteric coating strategy to preserve the biopharmaceutical performance of a silica-solidified lipid-based formulation. Methods and Results: The model weakly basic BCS Class IV drug, abiraterone acetate, was loaded into a lipid-based formulation and solidified using mesoporous silica nanoparticles. In an in vitro lipolysis model, introducing the formulation only after the onset of the intestinal phase led to lower precipitation and over 50% greater drug presence in the aqueous phase compared to a two-stage gastric-intestinal digestion. In an in vivo pharmacokinetic study in Sprague Dawley rats, the silica-lipid formulation (6 mg/kg), delivered in gelatine minicapsules enteric-coated with Eudragit L100-55, resulted in a 2.6-fold higher systemic exposure compared to the non-coated formulation (p < 0.0001). Conclusions: These findings support the use of enteric coating for lipid-based formulations and silica nanoparticles containing weakly basic drugs as a strategy to maintain formulation integrity until reaching the small intestine.