Thanks for posting query on Healthcare Magic
You doctor is very correct, there are lots of drug interaction
with antiepileptic drugs. Some medications reduce the efficacy of antiepileptics even though you are take same dose.
Usually no medication is required for diarrhea
except maintain hydration and electrlytes. If loose motion
is due to bacterial infection then only antibiotic is given. Commonly used antibiotic for this problem is ofloxacillin and ornidazole
with my best knowledge it does not has significant interaction.
hope you find useful for your query