What is the difference between Azulfidine Entabs 500 mg and Sulfazine ED 500 MG?

My mother has been on Azulfidine Entabs 500 MG for many years, however, they have changed

her prescription to Sulfazine EC 500 mg. Are there any differences in the effects and/or

purposes of the above. She is convinced the Entabs were more successful in her treatment.