Biorelevant dissolution behaviour of the amorphous sodium salt and amorphous acid forms of furosemide was evaluated, together with investigations of the solid state changes during in vitro dissolution in medium simulating the conditions in the small intestine. UV imaging of the two amorphous forms, as well as of crystalline furosemide salt and acid showed a higher rate of dissolution of the salt forms in comparison with the two acid forms. The measured dissolution rates of the four furosemide forms from the UV imaging system and from eluted effluent samples were consistent with dissolution rates obtained from micro dissolution experiments. Partial least squares-discriminant analysis of Raman spectra of the amorphous acid form during flow through dissolution showed that the amorphous acid exhibited a fast conversion to the crystalline acid. Flow through dissolution coupled with Raman spectroscopy showed a conversion of the amorphous furosemide salt to a more stable polymorph. It was found by thermogravimetric analysis and hot stage microscopy that the salt forms of furosemide converted to a trihydrate during dissolution. It can be concluded that during biorelevant dissolution, the amorphous and crystalline furosemide salt converted to a trihydrate, whereas the amorphous acid exhibited fast conversion to the crystalline acid.
Bibliographical noteFunding Information:
The authors would like to acknowledge the Villum Kann Rasmussen Foundation for financial support, together with NAnoMEChanical sensors and actuators, fundamentals and new directions (NAMEC) – a VKR Centre of Excellence. Furthermore, Dr. Kaisa Naelapää is acknowledged for assistance with the Raman flow through setup and optimisation of the testing procedure.
- Amorphous form
- Biorelevant dissolution
- Raman flow through dissolution
- Solid state conversion
- UV imaging
ASJC Scopus subject areas
- Pharmaceutical Science