Lack of effect of clonazepam on serum levels of diphenylhydantoin, phenobarbital and carbamazepine.

The influence of clonazepam on steady-state serum levels of diphenylhydantoin, phenobarbital and carbamazepine was studied in 22 patients with epilepsy receiving one or two of these drugs. Clonazepam was given in slowly increasing doses for 2 weeks until a maximum dose of 4-6 mg per day was reached; thereafter the dose was kept constant. The serum levels of diphenylhydantoin, phenobarbital and carbamazepine were determined once a week for at least 6 weeks. During clonazepam medication in ordinary doses the serum levels of the drugs in question were unaltered. Thus, it is unlikely that the antiepileptic effect of clonazepam in these patients even partly may be due to increased serum levels of these other drugs mentioned.