Acute intermittent porphyria and epilepsy: safety of clonazepam.

A young woman with acute intermittent porphyria (AIP) and juvenile myoclonic epilepsy began to have generalized tonic-clonic seizures (GTCs) at age 13. Subsequently, she had myoclonic seizures, which were often precipitated by visual stimulation, tended to occur in the morning, and sometimes evolved into GTCs. Valproate (VPA) resulted in a worsening of latent AIP, and treatment with a combination of phenytoin (PHT), carbamazepine (CBZ), and clonazepam (CZP) led to severe neuropathy of AIP and an electrolyte imbalance. These conditions were improved by water restriction, infusion of high doses of carbohydrates, and discontinuation of all antiepileptic drugs (AEDs) except for CZP. CZP appeared to be effective both in improving GTCs and myoclonic seizures and did not induce any symptoms of AIP. CZP may be porphyrogenic but can be used safely at a low dose for treatment of epilepsy in patients with AIP.