Afinitor is used to treat certain kinds of cancers, tumors, or seizure disorders. In comparison, Zortress is used to help prevent organ rejection after a kidney transplant or a liver transplant.Both Afinitor and Zortress come as a tablet that you swallow. But these drugs have different strengths and dosages. They can cause different side effects, too.Because of all these differences, Afinitor and Zortress are not considered interchangeable. You should always take the medication and dose that your doctor prescribes.If you have questions about whether Afinitor or Zortress may be right for your condition, talk with your doctor.