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July 28, 2016 – CAF recently learned of a thalassemia patient with a kidney problem called Renal Fanconi Syndrome, likely due to deferasirox. We would like to answer several questions that often arise about this problem. Dr. Ellis Neufeld, Chair of CAF’s Medical Advisory Board, has provided answers to the following questions.
What is Renal Fanconi Syndrome?
This is a kidney problem that can be caused by any of several drugs. Dr. Fanconi was a distinguished Italian pediatrician, whose name is also applied to a rare genetic bone marrow problem, not to be mistaken with this acquired (non-genetic) problem. The kidneys have many jobs as they purify the blood, including maintenance of blood acidity (pH), blood electrolytes like sodium, potassium, choride and bicarbonate, and reabsorption of blood components that we need to keep inside the body (rather than lost in the urine) including sugar (glucose) and proteins. Many of these jobs are done by the kidney “tubules.”
What has this got to do with iron chelation and deferasirox?
Both forms of deferasirox (Exjade and Jadenu) may cause kidney problems in some but not all patients. If you take deferasirox, your physician will be checking for kidney issues from time to time, both by blood tests and occasional urine tests. The kidney problems are often dose-related but not always. Patients discovered to have a significant kidney issue with deferasirox should take at least a brief holiday from the drug, until the kidney problem is resolved.
Deferasirox seems to be a poison to the kidney tubules in patients who get renal Fanconi Syndrome. This can lead to disturbances of blood electrolytes, sometimes associated with vomiting, or with poor growth. Small children might be more sensitive to this problem.
Kidney issues (including Renal Fanconi Syndrome) can sometimes be resolved using lower doses. But if the lower doses aren’t sufficient to get rid of your iron, or if the kidney problem was very severe to begin with, or recurs on the lower dose, this is a time to consider the alternative chelators, deferoxamine and deferiprone.
Could the problem somehow be worse with Jadenu than Exjade?
The active ingredient of both brand name preparations is identical, so in this sense no. However, Jadenu is better absorbed by the body than Exjade. That’s a good thing for iron chelation! At the same time however, if more of the chelator is absorbed, the kidney may be exposed to higher levels as well. This is exactly why Jadenu has lower dosage recommendations and less mg per tablet than Exjade.
Are the kidney risks so severe that I should avoid deferasirox even if I haven’t had problems?
Not necessarily! deferasirox is the only oral “first line” chelator, and especially with Jadenu, it is more convenient than the other medications, and well tolerated by a large majority of patients. If you are concerned about cases of adverse effects that you have heard about, you should discuss this with your hematologist.
CAF thanks Dr. Neufeld for sharing his expertise with us on this matter.