Does alcohol reduce the effectiveness of anti-epileptic drugs?

Not really: Alcohol and its withdrawal state can induce seizures mediate by depletion and overactivation of neurochemicals including magnesium. We use some antiepileptic agents for seizure prevention, also as an anticraving ie topiramate

Yes: It can affect them in many different ways. First and foremost, alcohol itself can cause seizures, and in those dependent on alcohol, stopping can cause seizures too. In addition, alcohol has interactions which lower the levels of many epilepsy drugs, particularly Dilantin and tegretol, but many others as well. If you are on meds and drinking, talk to your neurologist asap and get help to quit.