All of the following statements are true about 6 mercapto purine except
**Core Concept**
6-Mercaptopurine (6-MP) is a purine analogue used in the treatment of acute lymphoblastic leukemia (ALL) and autoimmune diseases like rheumatoid arthritis. It is a prodrug that requires metabolic activation to exert its therapeutic effects.
**Why the Correct Answer is Right**
The correct statement about 6-MP is that it is a competitive inhibitor of xanthine oxidase, an enzyme involved in purine metabolism. This inhibition leads to increased levels of 6-thioguanine nucleotides (6-TGNs), which are responsible for the cytotoxic and immunosuppressive effects of 6-MP. The enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is also involved in the activation of 6-MP, converting it into 6-thioguanine nucleotides.
**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because 6-MP is not a direct inhibitor of dihydrofolate reductase (DHFR), an enzyme targeted by other chemotherapeutic agents like methotrexate.
**Option B:** This statement is incorrect because 6-MP is not primarily metabolized by CYP2C8, although it can be metabolized by other cytochrome P450 enzymes.
**Option C:** This statement is incorrect because 6-MP is not a substrate for P-glycoprotein (P-gp), a protein involved in multidrug resistance.
**Clinical Pearl / High-Yield Fact**
It's essential to monitor 6-MP levels and adjust the dose accordingly to minimize the risk of toxicity. Additionally, patients on 6-MP should be advised to avoid alcohol and avoid certain medications that can interact with this drug.
**Correct Answer:** A.