Mercaptopurine and allopurinol

[pharmacist 2010]

According to Rx Prep book: reduce dose of mercaptopurine by 25-33% if mercaptopurine and allopurinol are given concomittantlly. However, I checked Epocrates, it says decrease mercaptopurine dose by 66-75%. which one is correct?

Is anyone studying Rx Prep book for NAPLEX?


Thanks.

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[All4MyDaughter]

What did you learn in school? I learned that you reduce the mercapto dose to 1/4 to 1/3 the normal dose if given with allopurinol.

 

[BMBiology]

According to Rx Prep book: reduce dose of mercaptopurine by 25-33% if mercaptopurine and allopurinol are given concomittantlly. However, I checked Epocrates, it says decrease mercaptopurine dose by 66-75%. which one is correct?

Is anyone studying Rx Prep book for NAPLEX?

I think rxprep got it backward. I got this from Lexi-Comp:

"Reduce dose of mercaptopurine to approximately 25% of normal dose if used concomitantly with allopurinol. Monitor for toxic effects of mercaptopurine."

Therefore, you reduce by 75% (= 25% of normal dose).

 

[pharmacist 2010]

Thanks. What I learned from school is that reduce mercaptopurine to 25-33% of usual dose. I also checked prontopass, it says the same.

 

[BME103]

According to Rx Prep book: reduce dose of mercaptopurine by 25-33% if mercaptopurine and allopurinol are given concomittantlly. However, I checked Epocrates, it says decrease mercaptopurine dose by 66-75%. which one is correct?

Is anyone studying Rx Prep book for NAPLEX?


Thanks.

just curious, does anyone know the mechanism of this interaction?

 

[pharmacist 2010]

just curious, does anyone know the mechanism of this interaction?

The probable mechanism according to micromedex:
Concomitant allopurinol and mercaptopurine therapy can increase the toxicity of mercaptopurine. Allopurinol inhibits the first pass oxidative metabolism of mercaptopurine by xanthine oxidase. If both drugs are administered together, the dose of mercaptopurine should be reduced 65% to 75%.

 

[BMBiology]

just thought i bump this thread up for those studying; the board loves drug-drug interaction questions

 

[curioussss]

Does the dose of allopurinol matter?

 

[jorgeabaunza]

Does the dose of allopurinol matter?

Not sure if a dose is specified but do remember of a sentinel event where the patient passed away a couple years back 2/2 this drug interaction.