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Blood sugar control is very important to prevent further complications. There are different insulin
regimens. Your father is on Twice-daily mixture of short acting and intermediate insulin. This regimen works as follow: the morning short acting insulin takes care of breakfast; the morning long acting insulin takes care of lunch; the evening short acting insulin takes care of the evening meal; the evening long acting insulin takes care of overnight insulin needs. Problem with this regimen, if the insulin is premixed, it is hard to adjust insulin doses.
If the above regimen is not working for your father, he can go for multiple daily injections of short or fast acting insulin with one or two separate injections of intermediate or long acting insulin. For example: Lantus
are long acting insulin. They have to be given one time a day. This is basal insulin meaning available all the time for 24 hours. You have to adjust the dose of this insulin by measuring fasting blood sugar in morning. In addition to the Lantus/Levemir, patient needs to on any short acting insulin with meals. This short acting insulin (E.g. Actrapid) control post prandial blood sugar of every meal. They work only for 4-6 hours.
I suggest you discuss different regimens with your physician. Oral medications depend on whether he is Type 1 or Type 2 diabetic.