Effect of drying methods on removal of residual solvents from solvent-induced amorphous paclitaxel

We investigated the effect of solvents on the formation of amorphous paclitaxel and proposed an efficient strategy for the removal of residual solvents from solvent-induced amorphous paclitaxel. Amorphous paclitaxel was produced by solvent-induced method using non-polar solvents (methylene chloride, toluene, pentane, methyl t-butyl ether, chloroform, and acetonitrile/hexane (1 : 2, v/v)). The residual pentane and hexane levels easily met the International Conference on Harmonization (ICH)-specified values (5,000 and 290 ppm) by simple rotary evaporation. When the vacuum-dried sample was subjected to microwave-assisted drying, the ICH requirements for methylene chloride (600 ppm) and acetonitrile (410 ppm) were met by drying for 23 hr at 200 W and 3 hr at 200 W, respectively. However, residual toluene, methyl t-butyl ether, and chloroform concentrations did not meet the ICH-specified values (890, 5,000, and 60 ppm). The shape and size of amorphous paclitaxel particles were examined by SEM and XRD.