First of all, is your brother taking any other medications besides Zeptol? Interactions with those drugs can also result in unwanted side effects.
Other than this Zeptol is an anti convulsant, which means that it is given to prevent seizures. But it may also be given to in case of severe pain
in the cheek due to the facial nerve
So the question is this, is your brother having any seizures?
And getting back to your main question the most common side effects of zeptol are dizziness
, dry mouth
, nausea, unsteadiness and vomiting.
Other than that allergic reactions may occur, but I believe that in the case of you brother. there is no allergic reaction