In
the pharmaceutical industry, poorly water-soluble drugs require
enabling technologies to increase apparent solubility in the biological
environment. Amorphous solid dispersion (ASD) has emerged as an attractive
strategy that has been used to market more than 20 oral pharmaceutical
products. The amorphous form is inherently unstable and exhibits phase
separation and crystallization during shelf life storage. Polymers
stabilize the amorphous drug by antiplasticization, reducing molecular
mobility, reducing chemical potential of drug, and increasing glass
transition temperature in ASD. Here, drug-polymer miscibility is an
important contributor to the physical stability of ASDs. The current
Review discusses the basics of drug-polymer interactions with the
major focus on the methods for the evaluation of solubility and miscibility
of the drug in the polymer. Methods for the evaluation of drug-polymer
solubility and miscibility have been classified as thermal, spectroscopic,
microscopic, solid–liquid equilibrium-based, rheological, and
computational methods. Thermal methods have been commonly used to
determine the solubility of the drug in the polymer, while other methods
provide qualitative information about drug-polymer miscibility. Despite
advancements, the majority of these methods are still inadequate to
provide the value of drug-polymer miscibility at room temperature.
There is still a need for methods that can accurately determine drug-polymer
miscibility at pharmaceutically relevant temperatures.
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