Nano-co-crystals enhance the solubility and dissolution rate of poorly soluble drugs. The objective of this study was to obtain a better understanding of the dissolution process of nano-co-crystals and of the precipitation inhibition by various polymers. Itraconazole-succinic acid (ITZ-SUC) nano-co-crystal was chosen as model drug formulation to investigate the supersaturation and precipitation inhibition capabilities of various polymers (HPMC E5, HPMC E50, HPMCAS, HPC-SSL, PVPK30 and PVPVA64). The kinetic concentration-time profiles of nano-co-crystal were measured under non-sink conditions with in situ UV-VIS spectroscopy. HPMC E5 performed best by achieving the greatest extended supersaturation/precipitation inhibition. The precipitation inhibition capacity of HPMC E5 was proportional to its concentration. The maximum achievable supersaturation was proportional to the dissolution rate which can be modulated by the rate of supersaturation generation (i.e., addition rate or dose). Supersaturation could be prolonged significantly resulting in 2-5-fold increased area under the dissolution curves compared to nano-co-crystals alone. This effect was limited by a critical excess of undissolved particles with high specific surface area which acted as crystallization seeds resulting in faster precipitation. The study highlighted that a faster dissolution rate and the use of precipitation inhibitors were two key factors determining the extent and time of supersaturation of nano-co-crystals.
Keywords: In situ methods; Itraconazole-succinic acid co-crystal; Kinetic solubility; Nano-co-crystal; Precipitation inhibitor; Supersaturation.
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