Mechanisms of anticonvulsant drug action. II. Drugs primarily used for absence epilepsy.

The usefulness of the anticonvulsant drugs is determined by the mechanisms by which the agent acts and its pharmacokinetics. The general mechanisms of action of these agents include (1) effects on neurotransmitter action, (2) effects on repetitive neuronal firing mechanisms, (3) effects on neuronal networks, and (4) effects on neuronal ionic transport. Ethosuximide, valproic acid and clonazepam are used primarily in absence epilepsy. Valproic acid is also effective against generalized tonic-clonic epilepsy. Diazepam is used primarily in status epilepticus. Valproic acid enhances gamma aminobutyric acid (GABA)-mediated inhibition, reduces repetitive firing, and reduces both inhibition and excitation in neuronal networks. Clonazepam and diazepam enhance the inhibitory action of GABA, decrease inhibition in neuronal networks and affect calcium ion transport with lesser effects on repetitive firing. Ethosuximide reduces inhibition in neuronal networks, may interact with dopamine, and possibly affects sodium and potassium ion transport. Further work is needed to assess the degree of involvement of these effects in the anticonvulsant action versus the adverse effects of these agents.