An older barbiturate medicine for some seizures
Phenobarbital
An older barbiturate medicine used to control some types of seizure, including in babies, with strong sedative effects.
What is Phenobarbital?
Phenobarbital is one of the oldest epilepsy medicines, a barbiturate still used for some types of seizure and in newborn babies. It works by calming overactive electrical activity in the brain. Its main drawbacks are that it causes drowsiness and sedation, it can lead to dependence, and it must never be stopped suddenly because doing so can trigger seizures or a withdrawal reaction. It interacts with many other medicines because it speeds up how the body handles them, and it is a controlled drug, so it is prescribed and supervised carefully.
Education and reference only. This is a plain-language guide to Phenobarbital — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Phenobarbital is a long-established medicine of the barbiturate group, used mainly to control epilepsy and certain other seizures. Although newer epilepsy medicines have largely replaced it, it is still valued in some situations, including the treatment of seizures in newborn babies. It works by quietening down the brain's electrical activity, which also makes it sedating. It is taken by mouth, or given by injection in hospital, and because of its effects and its potential for dependence it is classed as a controlled drug and prescribed under careful supervision.
How it works
Phenobarbital boosts the action of a natural calming chemical in the brain, which dampens down the excessive electrical activity that causes seizures. By raising the threshold at which the brain 'fires', it makes seizures less likely. This same calming action on the brain is why it causes drowsiness and sedation. Because the brain adapts to its presence over time, the body can become dependent on it, which is one reason it should never be stopped suddenly: doing so can provoke seizures or a withdrawal reaction.
Company & origin
Originated / developed by: Generic (long-established).
One of the oldest epilepsy medicines, still used in the UK for some seizures and in newborn babies, prescribed as a controlled drug.
What it treats
Conditions Phenobarbital is used for
Practical use
How to take Phenobarbital
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth exactly as prescribed, at the same times each day, to keep a steady level in the body.
- Never stop it suddenly or miss doses, as this can trigger seizures or a withdrawal reaction; any change must be made slowly with medical advice.
- Avoid alcohol, which adds to the drowsiness and sedation.
- Give your prescriber a full list of your other medicines, as phenobarbital interacts with many of them.
- Be careful with driving or operating machinery until you know how drowsy it makes you.
Weighing it up
Advantages & disadvantages of Phenobarbital
Advantages
- An effective and long-established medicine for controlling some types of seizure.
- Still useful in particular situations, including treating seizures in newborn babies.
- Taken once or twice a day, with a long history of use behind it.
Disadvantages
- Causes drowsiness and sedation, which can affect daily activities.
- Can lead to dependence and must never be stopped suddenly because of seizure and withdrawal risk.
- Interacts with many other medicines and is a controlled drug needing careful supervision.
Practical use
Good to know
Two safety points stand out. First, never stop phenobarbital suddenly: the brain becomes used to it, so an abrupt stop can trigger seizures or a serious withdrawal reaction, and any change must be made slowly under medical guidance. Second, it interacts with a great many other medicines because it is an 'enzyme inducer', meaning it speeds up how the liver breaks down drugs, which can make other medicines — including some contraceptives and blood thinners — work less well. It is sedating, so it can cause drowsiness, and over time the body can become dependent on it. It is a controlled drug, so prescriptions are managed carefully. Drinking alcohol adds to the drowsiness and should be avoided. Tell your prescriber about everything else you take, as the list of interactions is long.
Who should not take it / use with caution
- People who have had a serious allergic reaction to phenobarbital or related barbiturates should not take it.
- It is used with great caution, or avoided, in people with significant breathing problems, because it can suppress breathing.
- It is used with care in people with liver or kidney problems, and in older people who are more sensitive to it.
- It is used with particular caution in pregnancy, where the specialist weighs the risks of seizures against those of the medicine.
Monitoring
- Reviewing how well seizures are controlled and watching for drowsiness and other side effects.
- Checking for interactions with other medicines, especially when these are started or stopped.
- Reviewing mood and, in long-term use, watching for signs of dependence.
Side effects
- Drowsiness, sedation, tiredness or unsteadiness.
- In children, sometimes the reverse — restlessness, irritability or overactivity.
- Mood changes, low mood or problems with memory and concentration.
- Rarely but seriously, serious skin reactions or, with high doses or overdose, dangerously slowed breathing, which need urgent medical attention.
Key interactions
- It speeds up how the liver handles many medicines, so it can make others — including some contraceptives and warfarin — less effective.
- Other sedating medicines, and alcohol, add to its drowsiness and should be used with caution.
- Levels of phenobarbital and other epilepsy medicines can affect each other, so combinations are managed carefully.
Available as: Tablets and an oral liquid taken by mouth, and a solution for injection given in hospital.
Answers
Phenobarbital: frequently asked questions
What is phenobarbital used for?
It is an older medicine used to control some types of seizure in epilepsy, and it is still used to treat seizures in newborn babies. It works by calming overactive electrical activity in the brain.
Why must I not stop it suddenly?
The brain becomes used to phenobarbital, so stopping suddenly can trigger seizures or a withdrawal reaction. Any change must be made slowly under medical supervision.
Why does it make me sleepy?
Phenobarbital calms the brain to stop seizures, and this same effect causes drowsiness and sedation. Avoid alcohol, which makes the drowsiness worse.
Why does my prescriber need my full medicines list?
Phenobarbital speeds up how the body breaks down many other medicines, making some — such as certain contraceptives and blood thinners — work less well, so all your medicines must be reviewed.
Why is it a controlled drug?
Because it is sedating and can lead to dependence, phenobarbital is classed as a controlled drug, so prescriptions are supervised and managed carefully.
Authoritative sources
- BNF
- NICE CKS
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