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Old 08-24-2013
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Question INH and B6 deficiency

Hello everyone!
This is my first message. I am an IMG starting my preparation for Step 1. This site is really helpful. Anyway, I was reading anemias and specifically sideroblastic anemia. Could someone please clarify the exact mechanism by which INH causes B6 deficiency and therefore sideroblastic anemia?
Thanks in advance!
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Old 08-24-2013
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INH toxicity stems from several causes, including deficiencies of pyridoxine (vitamin B6) and gamma amino butyric acid (GABA). INH induces a state of functional pyridoxine deficiency by at least two mechanisms. First, INH metabolites directly attach to and inactivate pyridoxine species. Second, INH inhibits the enzyme pyridoxine phosphokinase; this enzyme is necessary to activate pyridoxine to pyridoxal 5' phosphate, the cofactor in many "pyridoxine-dependent" reactions. Functional pyridoxine deficiency is the likely mechanism of INH-induced peripheral neuropathy.

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Old 08-24-2013
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This is what I read after your question. I didn't know details about B6 deficiency caused by INH. I hope this can be helpful for you. But I don' t think we need to know that for the exam, at least I hope so
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Old 08-24-2013
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You only need to know how B6 deficiency leads to Sideroblastic Anemia, and that INH causes the B6 deficiency. Pyridoxine mediates the synthesis of porphyrin and Heme, therefore it's deficiency will lead to lack of heme synthesis and excess in iron, and the iron deposits in RBCs forming the sideroblasts.
Also, OCPs cause B6 deficiency as well. So consider a young, sexually active woman, and a person with TB developing peripheral neuropathy and sideroblastic anemia in such a vignette.
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Old 08-25-2013
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Quote:
Originally Posted by Mo-tongji View Post
You only need to know how B6 deficiency leads to Sideroblastic Anemia, and that INH causes the B6 deficiency.
I imagined that this was kind of unnecessary detail, but it helps me when I understand something in depth.
Thanks for answering and also for the useful clinical vignettes.
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