Dimethadione (5,5-dimethyl-2,4-oxazolidinedione) is the N-demethylated metabolite of the anticonvulsant trimethadione. Dimethadione is considered to be a blocker of T-type calcium channel. Dimethadione also inhibits a specific potassium channel (Ikr) in HERG-transfected cells. It exerts teratogenic effect especially congenital heart defects. Dimethadione can be used for the measurement of regional tissue pH using positron emission tomography.

Trimethadione (brand name is TRIDIONE) is an oxazolidinedione compound that was developed as an antiepileptic agent for control of petit mal seizures that are refractory to treatment with other drugs. Tridione does not modify the maximal seizure pattern in patients undergoing electroconvulsive therapy and has a sedative effect that may increase to the point of ataxia when excessive doses are used. Trimethadione acts as a voltage-activated T-type Ca2+ channel blocker. Trimethadione is rapidly absorbed from the gastrointestinal tract. It is demethylated by liver microsomes to the active metabolite, dimethadione. Approximately 3% of a daily dose of tridione is recovered in the urine as the unchanged drug. The majority of trimethadione is excreted slowly by the kidney in the form of dimethadione.