Among all the excipients available for use in solid dispersions, the polyethylene glycols with molecular weights ranging from 1000 to 8000 and which exist in a waxy, semi-solid state at ambient temperature, have probably been the most thoroughly studied. Serajuddin et al. (40) demonstrated that solid dispersion formulations prepared from mixtures of PEG and polysorbate 80 may perform similarly to Gelucire 44/14. Although polysorbate 80 is liquid at room temperature, it forms a semi-solid matrix when mixed with PEG in up to a 4:1 ratio of polysorbate 80 and PEG (Fig. 8). It was hypothesized that polysorbate 80 was incorporated within the amorphous region of the PEG solid structure, and that the crystalline structure of solid PEG was minimally affected by polysorbate 80, because the two excipients were poorly miscible with one another (41).
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