4.2 Posology and method of administration
Adults, the Elderly and Children over 6 Years: Start with a small dose - 500mg daily with increments of 250mg every five to seven days until control is achieved with 1000 - 1500 mg daily. Occasionally 2000 mg in divided doses may be necessary.
Children aged 0-6 years old and those who are unable to swallow capsules should be given ethosuximide oral liquid. Currently available clinical trial data regarding the use of ethosuximide in the paediatric population are described in section 5.1.
Effective plasma levels of ethosuximide normally lie between 40 and 100 mcg per ml, but the clinical response should be the criteria for the regulation of the dosage. The half-life of ethosuximide in the plasma is more than 24 hours but the daily dose if large is more comfortably divided between morning and evening.
5.1 Pharmacodynamic properties
Ethosuximide gives selective control of absence seizures (petit mal) even when complicated by grand mal. It is also indicated for myoclonic seizures. Compared to other anti-convulsants, ethosuximide is more specific for pure petit mal.
The reduction of seizure frequency is thought to be achieved by depression of the motor cortex and elevation of the threshold to convulsive stimuli as seen by the suppression of the characteristic spike and wave EEG pattern.
In a double-blind randomized trial of 20 weeks duration in 453 children aged 2.5 to 13 years old with newly diagnosed childhood absence epilepsy, the efficacy, tolerability, and neuropsychlogical effects of ethosuximide, valproic acid and lamotrigine as monotherapy in childhood absence epilepsy were investigated. Those treated with either ethosuximide or valproic acid had higher freedom-from-failure rates (53% and 58%, respectively) than those given lamotrigine (29%; odds ratio with ethosuximide vs. lamotigine, 2.66; 95% confidence interval [CI], 1.65 to 4.28; odds ratio with valproic acid vs. lamotrigine, 3.34; 95% CI, 2.06 to 5.42; P<0.001 for both comparisons). In both prespecified and post hoc analyses, ethosuximide resulted in fewer attentional effects as compared with valproic acid (at week 16 and week 20, the percentage of subjects with a Confidence Index score of 0.60 or higher in the Conners’ Continuous Performance Test was greater in the valproic acid group than in the ethosuximide group (49% vs. 33%; odds ratio, 1.95; 95% CI, 1.12 to 3.41; P=0.03) and the lamotigine group (49% vs. 24%; odds ratio, 3.04; 95% CI, 1.69 to 5.49; P<0.001).