Understanding the solid-state behaviour of triglyceride solid lipid extrudates and its influence on dissolution

Three monoacid triglycerides differing in their fatty acid chain lengths were extruded below their melting temperatures. Physical characterization was conducted on the powders as well as the extrudates with a combination of DSC, XRPD and vibrational spectroscopy to get a deeper insight into the complex solid-state behaviour of lipids and solid lipid extrudates during processing and storage. The combination of extrusion temperature and friction was a key factor for the lipid polymorphic behaviour after extrusion. Polymorphic transitions had a strong influence on the dissolution behaviour due to crystallization of the stable β-form from the unstable α-form on the surface of the extrudate. These correlations help to understand the solid-state behaviour of lipids and to avoid process conditions which lead to unstable dosage forms. Tailor-made dissolution profiles for a model drug could be achieved using triglycerides of different fatty acid chain lengths as the dissolution rate is chain-length dependent. The solid-state form of the drug was unchanged after storage in accelerated conditions over 10 months. These studies demonstrate that although triglycerides are a promising basis for oral dosage forms, a good understanding and monitoring of the solid-state behaviour is mandatory to obtain reliable and reproducible dosage forms.