phenobarbital
Meaning of phenobarbital: One of the oldest seizure medicines still in regular use, kept for its long action and low cost rather than its comfort.
Definition of phenobarbital
Phenobarbital is a barbiturate medication used mainly to stop and prevent seizures. It works by boosting the effect of gamma-aminobutyric acid, the chemical messenger that quiets nerve cell activity in the brain, which both suppresses seizures and produces sedation. It stays active far longer than most other seizure drugs, and it is also used as a sedative and in withdrawal from alcohol and related sedatives.
How does it quiet the brain?
Nerve cells carry a receptor that opens a channel when gamma-aminobutyric acid lands on it, letting charge in and making the cell harder to fire. Phenobarbital binds to that receptor at its own site and holds the channel open longer each time it opens. Benzodiazepines act on the same receptor but make it open more often instead, and the difference is not academic. At high concentration a barbiturate can force the channel open with no natural messenger present at all, so the gap between a dose that sedates and a dose that suppresses breathing is narrower than it is with the drugs that later replaced it.
Where is it still used?
| Use | What it is doing there |
|---|---|
| Long term seizure control | Acting as an anticonvulsant for generalized and focal seizures, dosed infrequently because it lasts so long |
| Seizures that will not stop | Given in hospital when first and second line drugs have failed |
| Newborn seizures | Long established as a first choice in that age group |
| Alcohol and sedative withdrawal | Standing in as a sedative for the drug being withdrawn, then wearing off slowly |
Why has its use narrowed?
Three reasons, none of which is a failure of effect. It sedates, and in children it can bring irritability, overactivity and difficulty with learning that families notice. It speeds up the liver enzymes that clear other drugs, so it quietly lowers the levels of many medicines taken alongside it, including some hormonal contraceptives and blood thinners. And tolerance and physical dependence build with continued use, so stopping abruptly can provoke withdrawal seizures. Newer seizure medicines carry lighter versions of these problems, which is why they are usually reached for first. Phenobarbital has not disappeared, though. It is cheap, stable without refrigeration, available as a tablet, a liquid and an injection, and it remains listed among the medicines a basic health system is expected to stock, so in much of the world it is still a mainstay rather than a relic.
Used in a sentence
Phenobarbital was continued to maintain seizure control following the patient's diagnosis of epilepsy.
Good to know
Phenobarbital is a barbiturate used mainly as an anticonvulsant and sedative, not as an antipsychotic, a distinction worth noting since sedating, mood-altering medications are sometimes conflated with the separate class of medications used to treat psychosis.