Safety of anticonvulsants in hepatic porphyrias

Because acute attacks of porphyria may be precipitated by anticonvulsants, a therapeutic dilemma arises when seizures complicate hepatic porphyria. The list of unsafe agents includes barbiturates, primidone, phenytoin, mephenytoin, ethotoin, ethosuximide, methsuximide, phensuximide, and trimethadione. Agents are considered unsafe if they induce experimental porphyria in animals, and short trials in patients are unreliable for screening. Using drug incubation in chick-embryo hepatocyte culture, we found that porphyrin was increased by carbamazepine, clonazepam, and valproate. These agents should probably be avoided or used with caution in porphyric patients. Alternative approaches to acute porphyric attacks with seizures are discussed.