Phenobarbitone

Side effects

All medications have side effects. Not everyone will experience side effects.

Below are some possible side effects your child may experience

Sedation:

• If your child is drowsy or suffering from tiredness please discuss this with your doctor.
• It is not uncommon in the first 2 weeks of starting the drug to be more tired than usual, however if it continues beyond this, you should seek help.
• If significant drowsiness occurs seek help immediately

Rash

• If your child develops a rash, there are important features to look for such as: your child may rarely develop red eyes, red mouth, and/or blisters around the mouth, nose and lips.
• If your child develops any of these symptoms please call your doctor immediately.
• The drug may need to be stopped immediately but under medical supervision.

Other possible side effects

• Hyperexcitability or behavioural changes such as aggression
• Respiratory depression (taking breaths that are shallower or slower than usual)
• Difficulties with balance and coordination
• Reduced blood pressure (usually seen when doses are given intravenously in an emergency setting).

Interactions

• There are some drugs that interact with phenobarbitone and can alter its level in the blood.
• Phenobarbitone can also change the level of other medications in the blood, so always tell your doctor that your child is taking phenobarbitone. This is also important if you are giving your child herbal or complementary medicines. The doctor can check to make sure they are compatible.
• Phenobarbitone, if used with other medicines that also cause sleepiness may have an additive effect.

Need-to-know

• If phenobarbitone is withdrawn, it must be done slowly and under medical supervision to prevent an increase of seizures and other symptoms of withdrawal.
• Phenobarbitone may cause excessive  sleepiness and interfere with breathing, particularly in a child with breathing, swallowing and/or movement problems..

Monitoring and medication levels

Levels of phenobarbitone can be unpredictable and need to be monitored in the blood, especially when the medication is started and with any changes in dose. Phenobarbitone levels are usually taken before the medication is due (trough level), and as advised by your doctor.

Pregnancy and contraception

If a pregnancy is planned, a discussion with your neurologist is recommended. For further information, refer to the Contraception and Pregnancy section.

Disclaimer

The information provided in this handout is limited and does not replace the need for a medical consultation. It is very important you speak to your doctor about all aspects of your medication including side effects when medication is first prescribed. Report any concerns to your doctor promptly.

Information last reviewed: 09/06/2023.