Although aspirin has been reported to be more stable in moisture-freepolyethylene glycol (5), its stability data in a water-polyethylene glycolcombination are not available in literature. In polyethylene glycol, aspirinis hydrolyzed by a process of transesterification with an activation energyof 20.1 Kcal/mole (5), resulting in much higher stability compared withwater alone. Therefore, the water-polyethylene glycol 400 (4:1,v/v)solvent system is superior to water as a vehicle for aspirin in terms of bothsolubility and stability.