Lyophilization of cosolvent systems may be a beneficial way of enhancing both physical and chemical stability of a drug product. The objective of this research is to establish whether cosolvent systems commonly used in the formulation of poorly water-soluble drugs can be successfully lyophilized. Polyethylene glycol (PEG) 400 was selected because it is widely used and can be easily frozen. The addition of PEG 400 to commonly used bulking agents, such as mannitol, sucrose, or polyvinylpyrrolidone, caused a significant change in the thermal properties of the bulking agents as observed by modulated differential scanning calorimetry. In addition, PEG 8000 was evaluated as a bulking agent because it also can function as a cosolvent in solution and forms an acceptable cake after lyophilization. Addition of PEG 400 to PEG 8000 caused negligible changes in the thermogram of this bulking agent. Surprisingly, the combination of PEG 8000 and PEG 400 forms a solid lyophilized cake. The current system can be best described as the lyophilization of a miscible solution of PEG 8000 and PEG 400 resulting in a lyophile that has a crystalline structure of PEG 8000 which is able to support PEG 400.
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