Pharmacokinetics and interactions of antiepileptic drugs.

The pharmacokinetics and drug interactions of the agents of choice for treating epilepsy are examined. For effective treatment of epilepsy, target serum antiepileptic drug (AED) concentrations must be reached quickly and maintained. AEDs for acute treatment are formulated for quick absorption, while maintenance therapy is usually administered orally. AEDs have narrow therapeutic ranges. Individual differences in response necessitate that optimization of each regimen be based on the individual patient's clinical condition. Agents of choice for acute treatment are diazepam, lorazepam, midazolam, valproic acid, and phenytoin. Phenytoin, carbamazepine, valproic acid, phenobarbital, and benzodiazepines are typically used in maintenance therapy. The absorption, distribution, and metabolism or excretion characteristics of AEDs must be taken into account in optimizing the therapeutic regimen. Different AED formulations can have different absorption profiles. Drug interactions can affect all aspects of the pharmacokinetics of AEDs and should be considered when agents are removed from a regimen, as well as when they are added. Various factors can threaten seizure control and cause unexpected toxicity. Such problems can be avoided or controlled if the pharmacist is aware of the pharmacokinetics and potential interactions of the AEDs involved.