> Western Medicines > Phenobarbital


Used for:Sedation, Treatment and prevention of seizures and epilepsy
Chinese name:

What is Phenobarbital for?

Phenobarbital is a long-acting barbiturate sedative, hypnotic and anticonvulsant working by depressing the central nervous system, hence used for sedation, and treatment and prevention of seizures and epilepsy.

How to use it?

Phenobarbital is available in Hong Kong as injections, syrups and tablets. It can be taken with or without food. If it is to be injected into muscles, inject deep into muscle at a volume of less than 5 mL per injection site to minimize tissue irritation.


Oral, intravenous, intramuscular: 30-120 mg daily in 2 to 3 divided doses increased up to 400 mg daily.


Preoperative sedation
Intramuscular: 100-200 mg 60-90 minutes before operations


Maintenance of seizures
Oral, intravenous: 2 mg/kg daily in divided doses

Oral: 3-6 mg/kg daily in divided doses


Status epilepticus
Intravenous: 15-20 mg/kg daily in divided doses

Intravenous: 15-20 mg/kg daily in divided doses up to 1000 mg per dose

What are the side effects of Phenobarbital?

The common side effects of Phenobarbital include, but not limited to, hallucinations, drowsiness, bradycardia, hypotension, agitation, headache, skin rash, nausea and vomiting and pain at injection site.

Who should not take Phenobarbital?

  • People who are allergic to Phenobarbital or any component of the formulation or other barbiturates
  • Patients with marked hepatic impairment
  • Patients with dyspnea or airway obstruction
  • Patients with porphyria

For those being administered with IV infusion:

  • People with a history of sedative abuse
  • Patients with nephritis

Pharmacist Tips:

  • Inject deep into muscle at a volume of less than 5 mL per injection site to minimize tissue irritation.
  • Do not drive or operate machinery after taking Phenobarbital.
  • Avoid drinking alcohol while being on Phenobarbitone as it will make you excessively drowsy.

Common dosing schedule:
Oral Phenobarbital is to be taken at divided doses, usually 2-3 times. Take it with meals for convenience.


For the injections, they are to be injected when you are hospitalized.


This schedule is for reference only, adjustments may be made according to individual needs.


Some common medications Phenobarbital may interact with:

Phenobarbital may interact with many other medications. Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Phenobarbital in Hong Kong?

In Hong Kong, Phenobarbital is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.


For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk

Need more information?

For detailed information about the use of Phenobarbital in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.

Brands in Hong Kong
Available dosage
  • 15mg/5mL (Syrup)
  • 30mg / 60mg (Tablets)
  • 200mg/mL (Injections)
Drug class
Hypnotics, Anticonvulsants
Sub class
Alternative Names
Other drugs in same class