Administering medications to someone with Alzheimer’s disease is often a painstaking and challenging process.
Your dad’s combativeness is rooted in his failed attempts to actually communicate something to you.
Perhaps you could first try to find the source of his apprehension about taking his meds. Does he have trouble swallowing, which causes discomfort in taking his pill? Does the pill possibly have an unpleasant aftertaste? Is the time of day when taking the medications causing the anxiety? Was there something in his younger life that made him nervous about taking pills?
Make sure you prepare the environment before you start the process of giving him his medications. The setting should be calm and free of disruptions. Play some soft music. Walk your dad through the steps of what you are going to do, i.e., "Dad, it's time to take your medicine that the doctor wants you to take. (pause) Drink some water first. (pause) Here's your first pill. (pause) Make sure to swallow." Use short, simple instructions, don't rush, and allow him as much as possible to be empowered to take his medications on his own terms.
Sometimes just the sight of pill bottles can cause anxiety. It might be a good idea not to display any pill bottles while giving your dad his medications. This could be overwhelming for him. Before the designated time for his medications, take the pills out of each bottle, leaving the bottles out of sight. Try giving him one pill at a time.
If you are his regular caregiver, it might be that he is just taking his aggression out on you alone. Try giving the responsibility to another close relative and redirect prior to the taking of medications by engaging your dad in an activity he enjoys, or just by offering some social stimulation and compliments to ease his anxiety about taking his pills.
If the pills are large or hard to swallow, consult with his physician or pharmacist to see if they can be crushed and mixed with applesauce or yogurt.
If his combativeness escalates, set everything aside for a few minutes and try again. Keep in mind that his behaviors will change over time, so you may need to constantly modify your procedures.
As always, consult his physician or pharmacist with issues out of the ordinary in giving your dad his medications. It might be that the medications could be adjusted to be taken at a better time of day for your dad, when he is typically in a more congenial and willing mood.