Evaluating dissolution characteristics of different products (e.g. IR and ER) using different methods is like measuring temperatures of a drink and meal/bread using two different scales to justify that they have different contents and/or are prepared differently. Bizarre!
It is hard to believe that we are to follow such unscientific, illogical and invalid reasoning and practices in this day and age.
If two different temperature scales (or thermometer scales) are used to monitor drinks and meal/bread temperatures, how will one establish which one is hotter/colder than the other?
Similarly, if dissolution/release characteristics of different products are to be measured using two different scales (in this case, methods, in particular, product-specific methods), then how will one know which one is of faster release and which one is slower release type?
In conclusion, using the current practices of dissolution testing, one never determines the dissolution/release characteristics of any product. Therefore, for appropriate testing, it is essential to have a single and product-independent tester and/or method.