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Luminal / Phenobarbital

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1 Luminal / Phenobarbital on Wed Sep 30, 2009 12:45 pm


Phenobarbital (fee-noe-bar-bih-tal) is a generic medication manufactured by several companies. It is the oldest epilepsy medicine still in use. In 1912, two independent teams of chemists created the drug under the name of Luminal.

Phenobarbital is a barbiturate (bar-BICH-er-it), a type of medicine that is used to bring on sedation or sleepiness. This can be a disadvantage, along with behavioral changes and the risk of withdrawal seizures.

The advantages of phenobarbital are its long history of use, low cost, and effectiveness. It has a long half-life (that is, it stays in the body for a long time). This keeps the level of medication in the blood relatively stable over the course of the day even when it is taken in only one daily dose (often at bedtime).

It is approved for add-on (adjunctive) therapy for partial and tonic-clonic seizures. It has been used alone for more than 80 years, however, to treat partial and tonic-clonic seizures. It is also used for treatment of status epilepticus.

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 given—60 to 90 mg per day may be enough for an adult—or 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.

Because phenobarbital has been used for so many years, doctors have been able to study and observe its long-term side effects extensively—an advantage, in some respects, over the new medicines. During the past several decades, however, most doctors have recommended phenobarbital only after trying several other seizure medicines because its side effects often outweigh its benefits (except for certain groups such as very young children). Because of its low cost, however, it may be used more frequently in situations where cost is a critical issue, such as in developing countries.

Because phenobarbital is a barbiturate, it depresses brain function, reduces the breathing and heart rate, and decreases blood pressure and body temperature. As a result, the most common side effect of phenobarbital is sleepiness or fatigue. Be careful with driving, operating machinery, or any other dangerous activity until you know how you react to this medication.

Other side effects include:

•hyperactivity (in children)
•impaired attention (in children and adults)
•memory problems
•decreased sexual interest (libido)
•slurred speech
•folate deficiency
•low calcium levels, bone loss

If you notice problems like any of these while you are taking phenobarbital, it's probably a good idea to discuss them with your doctor or nurse. You shouldn't stop taking phenobarbital or any other seizure medication without your doctor's advice.

Phenobarbital also has been found to reduce the effectiveness of oral contraceptives (birth control pills), so women who could become pregnant may want to consider another form of birth control.

Some studies have found greater problems with behavior and thinking in children taking phenobarbital than in children taking other seizure medicines. Some studies have found that phenobarbital worsens pre-existing hyperactivity and aggressive tendencies. Many physicians believe that phenobarbital sedates children, with a greater effect at higher doses. A number of studies have not found any sedation, however, perhaps because some children become extra alert and their scores cancel out those of sedated children. Nevertheless, the problems with phenobarbital should not be overestimated.

Taking supplements of both calcium and vitamin D may help to prevent bone loss. If you have been taking phenobarbital for more than 5 years, it might be a good idea to have a bone density test. If this easy, painless test shows significant thinning of your bones, your doctor may want you to see a bone metabolism specialist.

Long-term effects
Long-term use of phenobarbital can lead to changes in the soft tissues, including:

•joint pains mimicking rheumatism
•heel and knuckle pads
•frozen shoulder
•Dupuytren's contractures (shortening and thickening of tissue underlying the skin of the palm; corrective surgery may be needed)
•fibromas (fibrous tumors) of the bottom of the foot
•Peyronie's disease (hardening of a portion of the penis)
Women who may become pregnant should be aware that studies have suggested a connection between phenobarbital and a higher-than-expected incidence of birth defects.

There also is a danger to the baby from withdrawal symptoms if the mother has taken phenobarbital in the last few months of pregnancy, since barbiturates like phenobarbital cross the placenta into the baby.

Communicate with your doctor about the potential effects of phenobarbital if you are pregnant or plan to become pregnant. Since phenobarbital reduces the effectiveness of oral contraceptives (birth control pills), you should be especially cautious.

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