Your vet probably already has this set up but this is just a reminder have a CBC with platelets one week after dosing and prior to next dose. They should do a liver function tests initially before starting treatment and then every 3-4 months.
Good luck with the treatment, I am so sorry this is happening to you, we all have loved great dogs and lost them. As I have said before there are many here on the board who will hold your shoulders up while you go through this. Also remember as you go through this with Fritz make sure he is comfortable, and when the quality of life is not there anymore make the decision that is good for him. You will be in my prayers.