ABSTRACT
Although antiepileptic drugs produce an essential benecial eect in the treatment of epilepsy (Table 47.1), their use is also associated with unwanted side eects and/or drug pharmacokinetic interactions. Combination antiepileptic drug therapy is used for persons with epilepsy who do not respond to monotherapy (Perucca 2006). In addition, non-antiepileptic drug medications may be prescribed simultaneously to treat other concurrent diseases. Antiepileptic drugs such as carbamazepine, phenytoin, phenobarbital, and primidone may induce cytochrome P450 and glucuronyl transferase enzymes. is action of the antiepileptic drugs can reduce serum concentrations of drugs given simultaneously if they are metabolized by these enzyme systems. Drugs at risk of higher levels when used in combination with some other antiepileptic drugs include lamotrigine; tiagabine; several steroidal drugs; cyclosporin A; oral anticoagulants; and many cardiovascular, antineoplastic, and psychotropic agents. Although not an enzyme inhibitor, valproic acid may inhibit the metabolism of selected substrates such as phenobarbital and lamotrigine. e newer antiepileptic drugs are less likely to induce or inhibit the activity of cytochrome P450 and glucuronyl transferase enzymes. Oxcarbazepine, lamotrigine, felbamate, and topiramate (high dose) may increase the metabolism of oral contraceptive steroids, resulting in unwanted pregnancies. e newer antiepileptic drugs levetiracetam, gabapentin,
and pregabalin do not appear to be associated with unwanted drug pharmacokinetic interactions. Pharmacodynamic drug interaction eects also include the neurotoxic actions of concomitant use of antiepileptic drugs possessing similar mechanisms.
