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Abstract
The aim was to evaluate the long-term stability of cyclosporin A-loaded nanoparticle suspensions, stored at 8 and 25°C. The stability of freeze-dried samples was also investigated. Nanoparticles (NP) of poly-C-caprolactone (PZCL), a biodegradable polymer, were obtained by a modified nanoprecipita-tion method. A central composite experimental design was used to investigate the simultaneous effect of technological factors (temperature of the aqueous phase and needle gauge) and formulation variables (volume of acetone and the amount of polymer and surfactant). The effect of these variables on the stability of the 100–220 nm particles obtained was evaluated. The percentage of cyclosporin A (CyA) encapsulated in the NP suspensions stored at 8 and 25 °C for at least 3 months remained unaltered. Moreover, there was no change in the size of NP. After 4 months storage, the physical stability of the preparation was affected. NP aggregates could be observed by light microscopy. Reconstituted freeze-dried preparations showed a mean increase of 1% in the incorporated drug and also a considerable increase in mean size and size distribution. Additional experiments investigated the effect of freezing temperature (-70 and -196 °C) and of 5, 10 and 20% (w/v) cryoprotector (mannitol, sorbitol, glucose and threalose) on 100 nm particles. The addition of glucose and threalose at concentrations >10% permitted adequate reconstitu-tion of the freeze-dried product with conservation of the encapsulated CyA.