I doubt that one drug could reduce your dad's Hgb A1C to less than 7%, which
is usually the index for under control.
You dad may try it with diet and exercise to see if it works, repeat A1C
after three months. If still high, needs another medications.
Usually, if your dad is overweight and no kidney problems, metformin would
be another first choice.
Remember, diet and exercise go first, then medications!!!
Compliance with diet and exercise with medications is the key.