Matthew, I'll pray that your dad will do well on his medication and that, even though this was not the news you would rather have heard, your dad will benefit from his treatment this way.
I've learned, though it has been a hard at times, to try to focus on the goodness of each and every day, and that God gives us the strength only for today. His grace is always sufficient to meet our needs in the here and now, as the future will have its own set of concerns that we needn't worry about too much today.
Your dad's comfort and health are the reason for these medications in the first place, so the fact that he is well enough still to benefit from them -- even though you'd prefer that he not have to take them -- is a blessing.
My dad, when the end approached, could no longer benefit from the medication he had been prescribed for many years. As often happens, he got to a point where all we could do was to make sure he was comfortable, and though he was not conscious, we had time that we could spend with him without worrying that he was battling to breathe or for his heart to pump. In our case, we were fortunate that this period of time was brief.
My prayer is that that time for you and your family will be far down the road.
Trust and be strong, friend.