<s>[INST] My father - 70yrs now, is suffering from epilepsy for last 35/40 years. I have kept him under my close supervision for last 20 years. He takes EPTION (Phenytoin) 250 mg daily but off late he is again suffering from low borderline serum phenytoin level. Doctors are not advising to increase phenytoin anymore. What to do? He is facing some dizzyness also. [/INST] Hi,Thanks for asking.Based on your clinical history and query, my opinion is as follows:1.  Epilepsy patients are treated with phenytoin and dosage is usually reduced slowly over years.2. At present your father serum phenytoin level is low, but there have been no episodes.3. As there are no episodes, no further  increase is necessary. Dizziness could be a side effect of phenytoin rather than the cause. Phenytoin is not useful in dizziness. Increasing dosage might cause complications.Hope it helps.Any further queries, happy to help again. </s>