Preparation and in vivo ocular absorption studies of disulfiram solid dispersion

Disulfiram, a dimer of diethyldithiocarbamate (DDC) which is a strong radical scavenger, is known to prevent cataract development. However, disulfiram is hardly absorbed from the cornea and its bioavailability is extremely low. In this study, we attempted to prepare disulfiram solid dispersion for the improvement of ocular bioavailability. Solid dispersions of disulfiram were prepared by either an evaporation method or a spray-drying method, using polyvinylpyrrolidone (PVP) as a carrier. Preparations were analyzed by scanning electron microscopy, powder X-ray diffractometry and differential scanning calorimetry, and confirmed to be a solid dispersion. The particle size of the solid dispersion prepared by the spray-drying method was smaller than the preparation by the evaporation method (spray-drying: 3.3+/-0.04 microm, evaporation: 34.3+/-18.0 microm). An in vivo ocular absorption experiment was conducted by instilling solid dispersions to rabbit eye and measuring the DDC in the aqueous humor. After instillation of disulfiram and PVP physical mixture, DDC was not detected in the aqueous humor. On the other hand, DDC appeared in the aqueous humor after the instillation of a solid dispersion. Maximal concentration and the area under the aqueous humor concentration-time curve were greater in the solid dispersion prepared by the spray-drying method than the preparation by the evaporation method. Disulfiram solid dispersion, especially prepared by the spray-drying method, improved ocular bioavailability.