Serum concentration of clonazepam and the therapeutic effect of the drug

The effect of other anticonvulsants (phenytoin, phenobarbitone and primidone) on serum clonazepam concentrations has been studied. Serum clonazepam concentrations were measured in 47 epileptic patients in whom a dose of clonazepam (3 mg or 6 mg) was added to existing therapy. 44 patients were receiving other anticonvulsants; 3 were not receiving any other medication. Patients on low doses of other anticonvulsants showed high clonazepam concentrations. Patients on multiple therapy with high doses of other anticonvulsants showed excessive side-effects on clonazepam and low serum clonazepam concentrations. We conclude that other anticonvulsants may reduce serum clonazepam concentrations and therefore that clonazepam is best given alone.