Phenobarbital is an anticonvulsant drug that has been used since 1912 and it is still one of the better drugs for this purpose. Phenobarbital is used to treat infants (ages 0-1 year) with any type of seizure disorder, and other children with generalized, partial or febrile seizures. It is also used for treatment of status epilepticus (seizures lasting greater than 15 minutes).

Formulations of phenobarinital

Phenobarbital is available in the following formulations:

  • 20 mg/5 ml liquid suspension
  • 15 mg tablets
  • 30 mg tablets
  • 60 mg tablets
  • 100 mg tablets

The suspension is a useful preparation for infants who cannot take tablets, but it does have an unpleasant taste and can be difficult for some children to swallow. Therefore it may be recommended for your child to take the very small tablet. The tablet also has a bad taste and should not be crushed. The tablet is easily swallowed by placing it in a spoonful of soft food, such as ice cream or pudding and having the child to swallow without chewing.

Correct phenobarbital dosage and therapeutic blood level

The usual dosage of phenobarbital is 3-6 mg per kilogram of body weight per day.

The blood level of phenobarbital that is found to prevent seizures in most people is between 10-40µg/ml.

Side effects of phenobarbital

Some children taking phenobarbital will experience behavior changes, including irritability, hyperactivity and/or sleep disturbances. The previously "busy" child who "never stops" may become more agitated and overactive while taking this drug. In some instances, these personality changes are temporary and diminish after a few days to a couple of weeks. In others, they persist until the drug is stopped. If the child's behavior becomes a significant problem when phenobarbital is begun, then a different anticonvulsant will be considered.

A small percentage of children are "allergic" to phenobarbital. Children with an allergy to phenobarbital will develop a skin rash 7-20 days after they begin taking the drug. This type of reaction usually requires immediate discontinuation of the drug and evaluation by a physician.

Toxic symptoms are symptoms experienced when the blood phenobarbital level is too high.

Early toxic symptoms may include

  • Staggering
  • Drowsiness 
  • Slurred speech

Common labs for monitoring phenobarbital

Scheduled monitoring of phenobarbital levels has increased its safety and efficacy. We will usually recommend checking a phenobarbital level 4 weeks after reaching a therapeutic dose and then every 4-12 months thereafter.

Phenobarbital drug interactions

Phenobarbital does affectthe metabolism or absorption of some medications, most of which are not commonly taken in childhood. You should inform your Neurologist if your child is taking any other medications. Your local pharmacist can often be helpful in informing you of known drug interactions between the medications your child is taking.

Last reviewed: 
June 2016

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