Question 3 of 10

(demo test)

Product Demo for RITE®

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  Axial T2 FLAIR (left); Coronal T1 with contrast (right)
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  Axial T2 FLAIR (left); Coronal T1 with contrast (right)
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  H&E
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  H&E

A 42-year-old man has the above findings on brain MRI and a brain biopsy shows the pathology presented above. He is treated with a 5 gram pulse of intravenous methylprednisolone over 5 days and then started on oral prednisone at 1 mg/kg/day. You counsel him and his wife and explain that if his disease progresses through, or fails to improve with, corticosteroids you would recommend pursuing intravenous pulses of cyclophosphamide. His wife is a nurse and asks you for more details on the mechanism of action of cyclophosphamide.

Which of the following responses is accurate?

A. it acts as an analog of endogenous purines

B. it is a calcineurin inhibitor

C. it is a dihydrofolate reductase inhibitor

D. it is a DNA alkylating agent

E. it is an inosine monophosphate dehydrogenase inhibitor

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Category:

Pharmacology/Chemistry

Topic:

Pharmacology/Chemistry

High Yield:

No

Your Answer:

U

Correct Answer:

D

Explanation:

This man has CNS vasculitis and cyclophosphamide is commonly used in the treatment of this disorder, particularly in severe/fulminant cases or in cases where there is progression through corticosteroids or dependence on prolonged high dose corticosteroids to control the disease. Cyclophosphamide is a prodrug that is metabolized by the liver to a phosphoramide mustard and acrolein. The phosphoramide mustard is the active alkylating component of the drug that is responsible for its cytotoxic and immunosuppressive effects. As an alkylating agent, the phosphoramide mustard forms DNA crosslinks and inactivates DNA. Acrolein is toxic to the bladder and accounts for the risk of hemorrhagic cystitis that is present with this drug. 

The remaining answer options refer to the mechanisms of action for the following drugs. 

A – azathioprine (6-mercaptopurine) 

B – cyclosporine A, tacrolimus 

C – methotrexate 

E – mycophenolate mofetil

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