I can only speak of two drugs that I know to be difficult on the liver (first hand experience).
Voltarin - only took a year before elevated liver enzymes appeared (i.e. liver toxicity)
Sulfasalazine/Azulfadine - I was on for 6 yrs and began to have issues with it this past March. I have transitioned over to the NSD now.
The azulfadine worked very well for me.
Take care,
Tim