Possible interactions of antiepileptic drugs (AED) and underlying pharmacokinetic and pharmacodynamic principles are considered. Prescription of several AED simultaneously, or combinations of AED with drugs of other categories may modify their absorption, distribution, metabolism or excretion, which might lead to complicated interactions. Liver metabolism inducing AED may affect biotransformation of concomitantly taken drugs of other categories. Incomplete renal elimination of AED may occur in elderly patients, that sometimes require dose reduction.