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Phenobarbital Level

Published: July 27, 2026Updated: August 25, 2026

The phenobarbital level measures the concentration of the anticonvulsant drug phenobarbital in the blood, used primarily for managing seizures and epilepsy.

Quick summary

Blood test to monitor phenobarbital concentration for seizure control.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
mg/L
Clinical utility
monitoring
Result kind
quantitative
FDA-cleared
Roche Phenobarbital, Abbott Phenobarbital, Siemens Phenobarbital
interpretation: {"text":"Levels below 15 mg/L may indicate insufficient drug concentration for seizure control.","label":"Low"}; {"text":"Levels above 40 mg/L may lead to toxicity, causing symptoms such as drowsiness, confusion, or even coma.","label":"High"}

Phenobarbital is a long-acting barbiturate used to control seizures and manage epilepsy. Monitoring its level in the blood is crucial to ensure therapeutic efficacy and avoid toxicity.

The therapeutic range for phenobarbital is generally considered to be between 15–40 mg/L. Levels below this range may not provide adequate seizure control, while levels above may lead to adverse effects.

Regular monitoring of phenobarbital levels helps in adjusting the dosage as needed, ensuring optimal treatment outcomes and minimizing side effects.

Frequently asked questions

Why is it important to monitor phenobarbital levels?
Monitoring ensures the drug is within the therapeutic range, providing effective seizure control without causing toxicity.
What are the symptoms of phenobarbital toxicity?
Symptoms include drowsiness, confusion, and in severe cases, coma. Monitoring helps prevent these adverse effects.
  1. 1
    Phenobarbital - DrugBankSource
  2. 2
    Therapeutic Drug Monitoring of Antiepileptic DrugsSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy