Antiepileptic Drugs Health Article

Definition

Antiepileptic drugs are all drugs used to treat or prevent convulsions, as in epilepsy.

Purpose

Antiepileptic drugs (AEDs) are designed to modify the structures and processes involved in the development of a seizure, including neurons, ion channels, receptors, glia, and inhibitory or excitatory synapses. These processes are modified to favor inhibition over excitation in order to stop or prevent seizure activity.

Description

The ideal AED would suppress all seizures without causing any unwanted side effects. Unfortunately, the drugs currently used not only fail to control seizure activity in some patients, but frequently cause side effects that range in severity from minimal impairment of the central nervous system (CNS) to death from aplastic anemia or liver (hepatic) failure.

Prior to 1993, the choice of an antiepileptic medication was limited to traditional drugs, as phenobarbital, primidone, phenytoin, carbamazepine and valproate. Although these drugs have the advantage of proven efficacy (effectiveness), many patients are left with refractory (break-through) seizures. Since 1993, many new medications have been approved by the United States Food and Drug Administration (FDA), expanding treatment options. The newer AEDs offer the potential advantages of fewer drug interactions, unique mechanisms of action, and a broader spectrum of activity.

The AEDs can be grouped according to their main mechanism of action, although many have several different actions and others work through unknown mechanisms. The main groups include sodium channel blockers, calcium current inhibitors, gamma-aminobutyric acid (GABA) enhancers, glutamate blockers, and drugs with unknown mechanisms of action.

Sodium Channel Blockade

Blocking the sodium channel in the cell membrane is the most common and the most well-characterized mechanism of currently available AEDs. AEDs that target these sodium channels prevent the return of the channels to the active state by stabilizing the inactive form. In doing so, repetitive firing of nerve impulses from the axon of the nerve is prevented. The blockade of sodium channels of nerve axons causes stabilization of the neuronal membranes and limits the development of seizure activity. Sodium channel blocker drugs include: carbamazepine, phenytoin, fosphenytoin, oxcarbazepine, lamotrignine, and zonizamide.

Calcium Current Inhibitors

Calcium channels are small channels in the nerve cell that function as the "pacemakers" of normal rhythmic brain cell activity. Calcium current inhibitors are particularly useful for controlling absence seizures. The drug ethosuximide is a calcium current inhibitor.