Hello,
although it's not quite right to decide treatment based on a single fasting
glucose measurement, given that this is a very high glucose level and that your father is not ill (having a fever or any kind of inflammation) I would suggest a few things.
If you haven't done so already then please check his glycosylated
hemoglobin.
You haven't written anything about his weight. If he is
overweight then loosing weight would benefit him regarding his blood sugar regulation.
Mild exercise (walking) is very beneficial for patients with
diabetes. It should be done every day (or every other day) and last at least 30 minutes each time.
Since his fasting glucose is too high, I suggest he adds
metformin (unless contraindicated) to his treatment. He should start with 500mg taken with his meal (noon or afternoon). If he has no serious side-effects he can increase the dosage (maximum 2-2.5 gr per day in 2-3 doses). 850mg twice a day is a good regimen. Keep in mind that increasing the dosage above 850mg twice a day will increase the likelihood of side effects disproportionately more than the anticipated benefit.
You can also increase
glimepiride dosage (if you haven't done so already). Maximum daily dosage is 6mg.
Finally, if his blood sugars are above 200 every day don't expect him to get to the target range with the addition of metformin. If he complies with body weight and eating advice and still his sugars are that high, then he'll probably need
insulin.
I hope I've addressed your concerns!
You may ask again if you need me to clarify anything.
Kind Regards!