indication

Used for the control of absence (petit mal) seizures that are refractory to treatment with other medications.

pharmacology

Paramethadione is an oxazolidinedione anticonvulsant similar to trimethadione that acts on the central nervous system (CNS) to reduce the number of absence seizures (often seen in epileptics). Absence seizures involve an interruption to consciousness where the person experiencing the seizure seems to become vacant and unresponsive for a short period of time (usually up to 30 seconds). Paramethadione acts on thalamic neurons in the thalamic reticular nucleus (which studies have shown to be associated with absence seizures, von Krosigk et al., 1993).

mechanism of action

Dione anticonvulsants such as paramethadione reduce T-type calcium currents in thalamic neurons (including thalamic relay neurons). This inhibits corticothalamic transmission and raises the threshold for repetitive activity in the thalamus. This results in a dampening of the abnormal thalamocortical rhythmicity proposed to underlie the 3-Hz spike-and-wave discharge seen on electroencephalogram (EEG) during absence seizures.

toxicity

Symptoms of overdose include clumsiness or unsteadiness, coma, severe dizziness, severe drowsiness, severe nausea, and problems with vision.

biotransformation

Primarily hepatic (mainly via cytochrome P450 isozyme 2C9), paramethadione is completely demethylated to 5-ethyl-5-methyl-2,4-oxazolidinedione, the active metabolite.

absorption

Rapid via the digestive tract.

half life

12 to 24 hours (however the half-life for the active metabolite is not known)