Changeover from azathioprine to mercaptopurine.

Hi,
I've been taking 150mg of azathioprine for several months now. Unfortunately I've now been suffering from terrible joint pain for quite a while as well. My consultant thinks it's either arthritis associated with the UC, or a side effect of the azathioprine.
I believe I may have to switch to mercaptopurine to see if the joint pain goes away. However, my GP mentioned I would have to go back to baseline (50mg) and work back up to the 150mg, which took 3 months to do with the azathioprine.

My worry is that I may flare again if I change over and have to build up the dosage again. Does anyone have experience of this? I take it I couldn't just switch straight over to 150mg of mercaptopurine from my azathioprine?

Cheers.

wow i havn't been on here for a while but im glad i did today and read about the dosage

I was on Aza for a few months .. went from 25 to 75  but only had a few weeks at 75 before my docs and IBD nurse jumped and told me to stop as i had a liver problem with it .

So i have tried again with mercaptapurine ( 6mp ) and was told to start at 25mg and be very careful not to miss a blood test , which i was as i was doubting there would be much difference between the 2 drugs .

 I seem to be fine with 6mp but i had increased to 37.5 ( 3/4 pill ) and then gone to 50mg   ,      all without seeing the consultant ( I got messed around and couldnt get an appt )

but i was wondering about going further to 75mg etc

Now I think i wont !! ... but will wait for the consultants advice /appt

thankyou for posting the dosage information ...i had not read that anywhere , although could have missed it ,  as i had in my head that it was the same drug but just broken down differently

Is it based on weight too ? ..im very skinny ( 5ft 10 , 60kg ) -

oh Okay

silly question perhaps , but do you know how they check how you're metabolizing it ?

I get regular blood tests , i.e ESR , FBC , Bone Profile , U & E Creatine , CRP and Liver 

would it be on that or is it a very specific test

Hi,
many thanks for replying.
I was at the consultant's today. It was a bit strange really, in that they made no mention of changing the drug regime.
However, I've to be referred to a rheumatologist, so we'll see what happens.
The bugger is I'm in pain now, and am somewhat fed up with it. It's really not good with my job either, it's difficult to even put a jacket on!

Hopefully it won't be long until I'm seen.

Anyone had any experience of seeing a rheumatologist / what happened?

Cheers.