I would suggest you ask the doctor if he will be testing to see if your husband has the right enzymes to metabolize 6mp.
I was on 6pm for 2 years and went off in 2006 when it affected my liver. Went on Imuran in 2009 after a bowel obstruction (thought I could go drug free for a while ... not).
I had a doctor in 2009 that kept playing with my doses and apparantly I didn't have the enzymes in the beginning to digest the drug, so I ended up having metabolite toxicity and my hair started to fall out. I am now on Pentasa and have a new doctor;) All symptoms reversed.
For those that can metobolize the drug, I hear it can provide long term benefits ... but do ask about pre-testing.