Because of an answer I got from someone more well read than I, I suspect the changes are a coincidence.
That response that I received in a thread said: "...You are right, nortriptyline is suppose to have a lower side effect profile than amitriptyline as amitriptyline is older and is one step further back in the bio-availability drug metabolism. Amitriptyline metabolizes to nortriptyline with the CYP2C19 pathway and to 10-Hydroxy amitriptyline (which is the less active hydroxy metabolite) through the CYP2D6 pathway so you take out a step with nortriptyline."
From this thread (near the end): http://beta.healclick.com/posts/6194
Long story short, nortriptyline is chosen first over amitriptyline by some fibro docs, because the side effects are less in this next generation version of amitriptyline, Particularly dry mouth and next day somnolence can be reduced on nortrip.
Post Edited (Rockon) : 3/17/2014 5:50:25 AM (GMT-6)