You may want to try giving your father turmeric.
I moved from the West Coast to the East Coast 9 years ago, because my mother reached the point where her Alzheimers had progressed to her not being able to live alone.
I gave her Aricept and then, in 2003, Memantine when it was not yet available in the US and one had to get a doctor's prescription and then get it from overseas. It is the standard combination therapy now, although far too many doctors still just use Aricept.
In late 2004, my then boyfriend told me about listening to NPR and they noted that Turmeric was being recommended. China and India have the lowest rate of Alzheimers and it was traced to the consumption of Turmeric in the diet. I got some and gave it to my mother, who became noticeably more alert in a rather short period of time (I noticed, when I gave her Memantine, she improved within 8 days. That turned out to the standard time I could see improvements for her).
Newsweek published a story on Alzheimers in the April 2005 issue, where the research specialist noted that the drug companies, after she issued a statement about turmeric, approached her and asked if she was trying to "put them out of business." By that point, mom had been using it for 4 months and, considering she was at stage 5, demonstrated a return of partial memory (she remembered events that happened a month ago), but more strikingly, a sense of appropriate behaviour ("Did I make a fool of myself when the pastor came over?" was her question to me one time).
Doctor's don't recommend anything that's not in drug form, but if you decide to try it, be aware that it can cause constipation after prolonged use, something another friend, who was 80, also mentioned to me after I recommended it to him. He was worried he was losing his memory. He said the turmeric helped, but he stopped using it because it caused constipation. I thought, so you'd rather lose your memory again than take something for the constipation, but that was his choice, so...
If you decide to buy it (health food stores sell it), make SURE it says it is 95% curcuminoids on the bottle.
I use it for arthritis, by the way, and it works well for that. I'm 60.
There are no other side effects, by the way. If you try it, you need to give him 900mg a day or even 1200mg. I had taken care of all my friends with AIDS prior to this, so I'm very aware of what doses work. If it had been known that this worked during the AIDS crisis, maybe we could have avoided the dementia so many of our friends developed.
It DOES work, but sadly, people don't realize that synthetic drugs -- Aricept, Memantine (which is also very good) can't penetrate the blood/brain barrier, and consequently, cannot get in to "scrub" the sludge that coats the nerve endings and thereby prevent the electrical impulses to "jump" from one nerve ending to the next one, but Turmeric is a natural ingredient, and the body does not prevent it from entering the brain, which is where the damage is being done.
I can't, obviously, force anyone to try it, but my experience is that it shows results faster than synthetics, and if you give it to him for a month, and he doesn't show any signs of improvement, there is no harm done (as I said, the constipation doesn't seem to start for a few months).