The drug release for the film sample was calculated and matched to release from the total film, in this case, is it valid for research purposes to accept an extrapolated value for cumulative release?
For highly water soluble drugs you can use but for hydrophobic drugs some concerned question may be raised because in few cases presence of drugs in the beaker further reduce the drugs solubility in significant manner.
So ......... saturation solublity is main concerned for such extrapolatation