Pharmacology of antiepileptic drugs

Several different types of chemical compounds are useful as antiepileptic drugs. Their mechanisms of action, as well as their physical structures, differ. Compounds such as carbamazepine, phenytoin, and probably valproate act by modifying ionic conductances, particularly sodium and calcium, in excitable membranes, thus limiting sustained high-frequency neuronal discharges. In contrast, barbiturates and benzodiazepines tend to affect gamma-aminobutyric acid (GABA) mediation of the chloride channel opening. Knowledge of drug mechanisms is important for choosing the proper drug for various seizures types. In addition, an understanding of antiepileptic drug pharmacokinetics, nontherapeutic effects, and interactions is essential for optimal therapy. The lack of uniform pharmacokinetics among patients and among different formulations of a drug can make it difficult to arrive at uniform criteria for both seizure control and determinations of toxicity. both pharmacokinetic and pharmacodynamic interactions can occur between antiepileptic medications and other drugs. Three major types of side effects with anticonvulsants can be identified: dose-related alterations of neurologic function, idiosyncratic reactions, and nonidiosyncratic function, idiosyncratic reactions, and nonidiosyncratic direct actions on other organ systems. These effects often compromise treatment.