Clinical effects and plasma concentrations of long-term clonazepam monotherapy in previously untreated epileptics

Ninety-three, previously untreated epileptics were subjected to clonazepam monotherapy. The plasma clonazepam concentrations were monitored to achieve optimal therapeutic effects of the drug. Within a mean duration of follow-up of 32 months, 57 (61.3%) of the 93 cases became seizure-free. The drug showed a high efficacy for complete seizure control of more than 80% for both simple partial seizures and primary generalized tonic clonic ones. The mean plasma level of clonazepam giving complete seizure control was 14.7 ng/ml (range: 3.0-34.6 ng/ml) in cases of generalized epilepsy, and 15.6 ng/ml (range: 4.5-42.3 ng/ml) in cases of partial epilepsy. There was a high correlation between the plasma level and the dose, but no correlation between the plasma level and the clinical effect of the drug. The variable therapeutic range and great interindividual differences in the optimal plasma clonazepam level imply that individually tailored regimens are necessary to achieve optimal therapeutic effects of the drug.