I don't know about
any other the others such as Remicade, Humira, etc. but, yes, Imuran (azathioprine) and 6MP (mercaptopurine?) do require periodic blood draws.
It seems to me that I saw periodic blood draws recommended for Pentasa too but in all my years on Pentasa a blood draw was never ordered for that despite I was on it 4-5 years before adding Imuran. Best thing is to check the drug insert and question if recommended tests aren't ordered.
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.