Ethotoin

Ethotoin exerts an antiepileptic effect without causing general central nervous system depression. The mechanism of action is probably very similar to that of phenytoin.

The latter drug appears to stabilize rather than to raise the normal seizure threshold, and to prevent the spread of seizure activity rather than to abolish the primary focus of seizure discharges.

Ethotoin is fairly rapidly absorbed; the extent of oral absorption is not known. The drug exhibits saturable metabolism with respect to the formation of N-deethyl and p-hydroxyl-ethotoin, the major metabolites. Where plasma concentrations are below about 8 μg/mL, the elimination half-life of ethotoin is in the range of 3 to 9 hours. A study comparing single doses of 500 mg, 1000 mg, and 1500 mg of ethotoin tablet demonstrated that ethotoin, and to a lesser extent 5-phenylhydantoin, a major metabolite, exhibits substantial nonlinear kinetics. The degree of nonlinearity with multiple dosing may be increased over that seen after a single dose, given the likelihood of plasma accumulation based on a reported elimination half-life of 6 to 9 hours and a dosing interval of 4 to 6 hours. Experience suggests that therapeutic plasma concentrations fall in the range of 15 to 50 μg/mL; however, this range is not as extensively documented as those quoted for other antiepileptics.

In laboratory animals, the drug was found effective against electroshock convulsions, and to a lesser extent, against complex partial (psychomotor) and pentylenetetrazol-induced seizures. In mice, the duration of antiepileptic activity was prolonged by hepatic injury but not by bilateral nephrectomy; the drug is apparently biotransformed by the liver.