Phenobarbital has been used to treat epilepsy since the early decades of the 20th century. It is still commonly used throughout the world because it is both effective and low in cost. Also, most people need to take it only once a day, so they are less likely to miss doses.
When given intravenously (by IV), it is effective in stopping the continuous convulsions of status epilepticus.
Phenobarbital is useful in controlling simple and complex partial seizures and generalized tonic-clonic seizures in patients of all ages. It has traditionally been considered the first choice to treat neonatal seizures (seizures in newborn infants). Most studies have found that phenobarbital controls these seizures in about one-third of the infants.
Phenobarbital also has been widely used to prevent recurrent febrile seizures (seizures accompanying a high fever in infants or young children). Because 2 days or more may be required to achieve a high enough level of medication in the blood to control seizures, giving phenobarbital after a fever begins will not be effective. Instead, it must be given daily. One study found that 4% of children treated with an adequate daily dose had a repetition of these seizures, compared to 20% of untreated children. Because febrile seizures usually cause no lasting harm, however, most children should not be given medication for them.
Studies have compared phenobarbital with other antiepileptic medications for treatment of newly diagnosed epilepsy. For instance, one large study compared phenobarbital with carbamazepine (Tegretol, Carbatrol), phenytoin (Dilantin, Phenytek), and primidone (Mysoline). All four medications were about equally effective when used alone to control tonic-clonic seizures in adults. (phenobarbital and phenytoin completely controlled them in 43% of patients, compared to 48% for Carbamazepine.) Carbamazepine more often succeeded in completely controlling partial seizures, however. One-third of those who continued to take phenobarbital for 18 months had complete control of their partial seizures, compared to nearly two-thirds of those who took carbamazepine.
Some doctors hesitate to prescribe phenobarbital because it has a reputation for causing unwanted side effects, especially drowsiness in adults and behavioral or learning problems in children. Side effects are much more likely to be troublesome if high doses are given60 to 90 mg per day may be enough for an adultor if too high a dose is given to start. It may be necessary to increase the dosage very slowly over several months. Drowsiness is more common when phenobarbital is first taken or when the dose is increased, but not everyone is affected and some people can take higher doses without trouble.
Phenobarbital is often used in combination with other seizure medicines if one medication does not fully control the patient's seizures. No single combination is perfect for everyone. Sometimes a series of combinations must be tried before finding what is best for the individual. Phenobarbital does interact with many other medications, so the dosages may need to be adjusted.
Reviewed February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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