Phenobarbital is a commonly prescribed barbiturate used as an anticonvulsant or sedative. Patients prescribed phenobarbital can take tablets or liquid phenobarbital, but injections are often used in clinical settings. Dosages will depend on the condition. Some people may require only one or two doses, but others may require long-term daily doses of phenobarbital.
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Phenobarbital overview
BRAND NAMES:
Sezaby (injection), Luminal, Donnatal
Generic Names:
Phenobarbital
Uses:
Treats seizures or provides sedation
Therapeutic Classes:
Anticonvulsant, sedative, barbiturate
Forms:
Tablet, oral solution (liquid), elixir (liquid), injectable
How it’s taken:
By mouth, injection
What is Phenobarbital used for?
The FDA-approved uses of phenobarbital include preventing or treating seizures, providing sedation before medical procedures, or helping people with insomnia fall asleep.
Key takeaways
Phenobarbital can cause drowsiness. You should not drive or do anything that requires concentration until you know how the medication makes you feel.
Phenobarbital can be habit-forming. To lower the risk of drug dependence and withdrawal, take the medication exactly as prescribed.
Avoid alcohol while taking phenobarbital. Mixing phenobarbital and alcohol can increase your risk of drowsiness.
Phenobarbital can be taken with or without food. If it hurts your stomach, taking it with food can be helpful.
Phenobarbital can interact with several other drugs. Before starting any new prescription or over-the-counter medications, vitamins, or supplements, tell your doctor or pharmacist.
What form(s) does Phenobarbital come in
Tablet
15 mg
16.2 mg
30 mg
32.4 mg
60 mg
64.8 mg
97.2 mg
100 mg
Oral solution (liquid)
20 mg/5 mL
Elixir (liquid)
20 mg/5 mL
Injection
65 mg/mL
130 mg/mL
What are common Phenobarbital doses?
For the maintenance treatment of seizures:
In adults: 30–100 mg taken by mouth one to three times daily OR 60–200 mg daily
In neonates, children, and adolescents: 3–8 mg/kg daily given in one or two doses
For the treatment of long-lasting seizures (status epilepticus):
In adults: 15-20 mg/kg intravenous injection with a second 5-10 mg/kg intravenous injection 10 minutes later if necessary
In neonates, children, and adolescents: 15–20 mg/kg as an intravenous injection followed by 5–10 mg/kg intravenous injection every 15 or 30 minutes as needed
For daytime sedation in adults: 30–120 mg tablets taken in two to three divided doses
For insomnia in adults: 100–200 mg taken at bedtime
For procedural sedation:
In adults: 100–200 mg intramuscular or intravenous injection given 60–90 minutes before the procedure
In neonates, children, and adolescents: 1–3 mg/kg intramuscular or intravenous injection given 60–90 minutes before the procedure
Find more detailed information about phenobarbital dosage, forms, and strengths here
Common Phenobarbital prescriptions
PHENobarbital
473ml of 20mg/5ml bottlePHENobarbital
15ml of 60mg/15ml cupPHENobarbital
5ml of 20mg/5ml cupPHENobarbital
100mg tabletPHENobarbital
15mg tabletPHENobarbital
16.2mg tabletPHENobarbital
30mg tabletPHENobarbital
32.4mg tabletPHENobarbital
60mg tabletPHENobarbital
64.8mg tabletPHENobarbital
97.2mg tablet
How to take Phenobarbital
Take this medication as instructed. Do not change the dose.
Follow the dosing schedule by taking doses once, twice, or three times daily. Do not take doses more frequently than prescribed.
For insomnia, take only one dose daily right before bedtime.
Phenobarbital doses can be taken on an empty stomach or with food.
How to take phenobarbital tablets:
Swallow the tablet with a drink of water.
If there’s a problem swallowing tablets, crush the tablet and mix it with food or liquid. Swallow the mixture immediately.
Store phenobarbital tablets at room temperature.
How to take phenobarbital oral solution or elixir:
The medication can be taken undiluted or mixed with water, milk, or fruit juice. Swallow the mixture immediately.
Measure doses with a calibrated oral syringe. Ask the pharmacist for one if it is not included in the carton.
Store phenobarbital oral solution or elixir at room temperature in a tightly closed, light-resistant container.
What to do if you miss a dose of Phenobarbital
Ask the prescriber about how to manage missed doses.
The prescriber may advise that missed doses be taken when remembered. Follow the prescriber’s instructions.
Do not take two doses at the same time to make up for a missed dose.
Phenobarbital contraindications
This medicine is not safe for everyone.
It is contraindicated (prohibited) for use in people who have had an allergic reaction to phenobarbital or other barbiturates, as well as people who have:
Significant lung disease that causes breathing problems or obstruction
Significant liver disease
Porphyria
A history of addiction to sedative medications
Phenobarbital warnings
Tell any doctor or other healthcare provider who treats you that you are using this medicine.
The prescribing physician will check your progress and the effects of this medicine at regular visits. Keep all appointments.
Tell the prescriber if you are pregnant, planning to become pregnant, breastfeeding, or have:
Any type of lung disease, particularly obstructive problems like asthma
Liver disease
Phenobarbital can cause serious problems, including:
Slowed breathing, apnea
Low blood pressure
Physical dependence or withdrawal
Severe allergic or drug reactions
This medicine can make you drowsy. Be careful when driving or operating machinery.
If phenobarbital is being taken daily, do not suddenly stop taking doses without consulting a physician. The doses may need to be gradually reduced to prevent withdrawal symptoms.
Phenobarbital can be habit-forming, so do not take more than prescribed or take doses more often than prescribed. Talk to the doctor if the medicine does not seem to be working.
Phenobarbital is a controlled substance. Giving or selling this drug to other people is dangerous and against the law.
Phenobarbital interactions
To prevent possible drug interactions, inform the prescriber about all the prescription drugs, over-the-counter medications, and supplements being taken, particularly:
Blood thinners
Corticosteroids
Oral contraceptives
Doxycycline, griseofulvin, phenytoin, valproic acid
Avoid drinking alcohol when taking phenobarbital.
Avoid medications that make you sleepy, such as sleeping pills, sedatives, benzodiazepines, or cold or allergy medicines, while taking phenobarbital.
Birth control pills may not work when taken with phenobarbital. Use another form of birth control while taking this medicine.
Tell other healthcare professionals about phenobarbital before they prescribe new medications.
Phenobarbital side effects
Serious adverse effects
Talk to the prescriber if you notice any signs or symptoms of a possible serious side effect, including:
Respiratory depression (slowed breathing)
Severe drowsiness, confusion, or slurred speech
Depression
Allergic reaction: hives, rash, itching, swelling of the face, mouth, or tongue, chest pain, trouble breathing
Less serious side effects
Sleepiness
“Hangover”
Depressed mood
Irritability, nervousness, or excitement (in children)
Nausea, vomiting
Balance or coordination problems (particularly in older people)
Injection site reactions
Sources:
Phenobarbital, StatPearls
Phenobarbital drug summary, Prescriber’s Digital Reference (PDR)
Phenobarbital elixir prescribing information, DailyMed (NIH National Library of Medicine)
Phenobarbital liquid prescribing information, DailyMed (NIH National Library of Medicine)
Phenobarbital sodium injection prescribing information, DailyMed (NIH National Library of Medicine)
Phenobarbital tablet prescribing information, DailyMed (NIH National Library of Medicine)
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