Highly supersaturated aqueous solutions by design of amorphous pharmaceutical nanoparticles
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For 40% of currently discovered drugs which are poorly water soluble, engineering amorphous nanoparticles with rapid dissolution and enhanced solubility can improve their absorption. Antisolvent precipitation by mixing organic drug solutions with aqueous solutions produced sub-300 nm amorphous nanoparticle dispersions. Polymeric stabilizers increased the nucleation rate by lowering the interfacial tension and adsorbed to particle surfaces to inhibit growth by condensation and coagulation. An increase in the stabilizer concentration decreased the average particle size until reaching a threshold where the particles were < 300 nm for the poorly water soluble drug, itraconazole. The amorphous itraconazole nanoparticle dispersions dissolved at pH 1.2 to produce high supersaturation levels up to 90-times the equilibrium solubility. The supersaturation increased with particle curvature, as described qualitatively by the Kelvin equation. A thermodynamic analysis indicated the stabilizer maintained amorphous ITZ in the solid phase with a fugacity 90-times the crystalline value, while it did not influence the activity coefficient of ITZ in the aqueous phase. Recovery of the amorphous nanoparticles from water was achieved by adding salt to desolvate the polymeric stabilizers and flocculate the particles, which could then be rapidly filtered. The flocculation under constant particle volume fraction produced open flocs which were redispersible in water to their original ~300 nm size, after filtration and drying. Amorphous particles were preserved, as flocs were formed below the drug's glass transition temperature. After flocculation/filtration, medium surface area (2-5 m²/g) particles dissolved rapidly in pH 6.8 buffer with 0.17% surfactant to an unusually large supersaturation up to 17, comparable to that for high surface area (13-36 m²/g) particles. However, the decay in supersaturation was much slower for the medium surface area particles, as the smaller excess surface area of undissolved particles produced slower nucleation and growth from solution. In contrast, the maximum supersaturation was far lower for more conventional low surface area solid dispersions of drug in polymers, because of crystallization of undissolved solid during slow dissolution. The ability to design the particle morphology to manipulate the level in supersaturation in pH 6.8 media, offers new opportunities in raising bioavailability in gastrointestinal delivery.