The addition of enalapril maleate to a casting solution for orodispersible films (ODFs) containing hypromellose and carbomer 974P as film forming agents (standard casting solution, SCS) caused a dose dependent reduction of the viscosity. This phenomenon was a serious problem in the preparation of ODFs with an increased enalapril load (> 1 mg per ODF) when using the solvent casting method.
The aim of the present work was twofold. Firstly, the influence of enalapril on the viscosity of SCS was studied in more detail. Secondly, two methods for increasing the enalapril load of an ODF were investigated that did not negatively influence the properties of SCS. The casting height was increased and the preparation of bilayered ODF, using the double-casting method, was explored. In the framework of the bilayered ODFs the compatibility between the film forming agents hydroxypropyl cellulose (HPC), sodium alginate (SA), hydroxyethyl cellulose (HEC) and the combination hypromellose–carbomer 974P (SCS) was investigated.Results and conclusions
We found that enalapril concentration dependently reduced the pH, thereby negatively influencing the gel formation and the viscosity of SCS.Results and conclusions
An increased casting height did not result in a proportionally increased enalapril load.Results and conclusions
The enalapril load could be doubled when a bilayered ODF containing two layers of SCS was produced.Results and conclusions
Finally, not all combinations of film forming agents could be used for the preparation of bilayered ODFs. Besides, the sequence in which the different polymer layers were casted affected the appearance of the ODFs. In conclusion, the best formulations were produced with the polymer combinations SCS/SCS and SCS/HPC.Graphical abstract
SEM images of bilayered orodispersible films showing (in)compatibility of polymers applied. Left: two layers of sodium alginate; right: one layer of sodium alginate and one layer of hypromellose combined with carbomer 974P.