Drug Interaction Report

MONITOR: Drugs that can increase plasma ammonia levels such as corticosteroids, haloperidol, or the anticonvulsants carbamazepine, topiramate, and phenobarbital may interfere with the therapeutic effects of phenylbutyrate therapy in the management of urea cycle disorders. Corticosteroids can cause the breakdown of body protein, which may lead to increased ammonia levels. The use of haloperidol has been associated with hyperammonemia in a young child with citrullinemia, an inherited disorder of ammonia excretion. The mechanism for haloperidol, carbamazepine, topiramate, and phenobarbital has not been established.

MANAGEMENT: Plasma ammonia levels should be closely monitored when corticosteroids, haloperidol, carbamazepine, topiramate, or phenobarbital are used in patients with urea cycle disorders receiving phenylbutyrate therapy.