title: Using Flory-Huggins phase diagrams as a pre-formulation tool for the production of amorphous solid dispersions: a comparison between hot-melt extrusion and spray drying.
abstract: OBJECTIVE
  Amorphous drug forms provide a useful method of enhancing the dissolution performance of poorly water-soluble drugs; however, they are inherently unstable. In this article, we have used Flory-Huggins theory to predict drug solubility and miscibility in polymer candidates, and used this information to compare spray drying and melt extrusion as processes to manufacture solid dispersions.
  
  
  METHODS
  Solid dispersions were prepared using two different techniques (hot-melt extrusion and spray drying), and characterised using a combination of thermal (thermogravimetric analysis and differential scanning calorimetry), spectroscopic (Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction methods.
  
  
  RESULTS
  Spray drying permitted generation of amorphous solid dispersions across a wider drug concentration than melt extrusion. Melt extrusion provided sufficient energy for more intimate mixing to be achieved between drug and polymer, which may improve physical stability. It was also confirmed that stronger drug-polymer interactions might be generated through melt extrusion. Remixing and dissolution of recrystallised felodipine into the polymeric matrices did occur during the modulated differential scanning calorimetry analysis, but the complementary information provided from FTIR confirms that all freshly prepared spray-dried samples were amorphous with the existence of amorphous drug domains within high drug-loaded samples.
  
  
  CONCLUSIONS
  Using temperature-composition phase diagrams to probe the relevance of temperature and drug composition in specific polymer candidates facilitates polymer screening for the purpose of formulating solid dispersions.
authors.affiliation: The Drug Delivery and Biomaterials Group, School of Pharmacy, Medical Biology Centre, Queen's University, Belfast, UK.
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Tian
authors.forename: Vincent
authors.initials: V
authors.lastname: Caron
authors.forename: David S
authors.initials: DS
authors.lastname: Jones
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Healy
authors.forename: Gavin P
authors.initials: GP
authors.lastname: Andrews
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods; D003460:Crystallization; D003890:Desiccation; D004337:Drug Carriers / Q000737:chemistry*; D004339:Drug Compounding / Q000379:methods*; D004355:Drug Stability; D015736:Felodipine / Q000008:administration & dosage / Q000737:chemistry*; D005615:Freezing; D006358:Hot Temperature; D006801:Humans; D011108:Polymers / Q000737:chemistry*; D012995:Solubility; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D004337:Drug Carriers; D011108:Polymers; D012996:Solutions; D015736:Felodipine
keywords: Flory-Huggins phase diagram; amorphous solid dispersion; hot-melt extrusion; physical stability; spray drying