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Phenobarbital Dosage Forms And Strengths

Last Updated: March 20, 2024

Authored by Roger Weiss, MD

Reviewed by Dr. Ash Bhatt

Phenobarbital has several purposes. The sedative effects of the medication are often utilized to assist in the treatment of numerous conditions and for particular medical purposes. Adequate Phenobarbital strength needs to be used for a particular purpose to avoid experiencing severe side-effects or certain complications.

The appropriate Phenobarbital therapeutic level in the blood depends on a variety of factors, with the age of the patient being an especially important factor. The reason why the drug is being used also affects how much of the chemical should be given to the drug. For example, Phenobarbital dosage for anxiety is different compared to using the medicine for insomnia.

Phenobarbital Forms And Strengths

While a general range of recommendations does exist for the use of this drug in patients, it is important to consider the fact that there are different Phenobarbital dosage forms. Some forms are preferred for particular uses, while others are generally used for a larger variety of purposes and to assist in treating several conditions.

Three primary dosage forms can be utilized in a patient. A physician will carefully consider the case and identify the best route of administration.

In tablet form, the dosage per pill generally ranges from 15mg up to 100mg. The specific options that are available include:

  • 15mg
  • 16mg
  • 30mg
  • 32mg
  • 60mg
  • 64.8mg
  • 65mg
  • 100mg

There are injectable solutions possible, as well. These are used in four different doses available, including:

  • 30mg per milliliter
  • 60mg per milliliter
  • 65mg per milliliter
  • 130mg per milliliter

In addition to these two dosage forms, an elixir is also available that is provided in a 20mg/5mL dose only.

Adult Dosages

When it comes to using this medication in adults, the dose is usually considerably higher compared to children. At the same time, it is crucial to understand what the appropriate Phenobarbital therapeutic range is for different conditions, as a Phenobarb overdose can be harmful to the patient or cause possible complications. Below, we share some common uses of the medication, as well as the appropriate Phenobarbital level that should be in the blood after taking the drug.

For Sedation

In some cases, adults may utilize the drug for inducing sedation. There are various reasons why a patient may need to use the medication for sedation. A dose between 30mg and 120mg can be provided to the patient. Individuals will often be started with a Phenobarbital 30mg tablet. If this dose does not work effectively, then the dosage may be increased to Phenobarbital 64.8, for example, or perhaps a higher option.

The maximum daily dose of the medicine that may be used for sedation is 400mg.

For Insomnia

The sedative effects of Phenobarbital are often utilized to help adults with insomnia sleep better at night. A 100mg Phenobarbital tablet is usually advised as a starting point for people who experience insomnia and sleeping difficulties during the night. The recommended dosage ranges up to 200mg. Some people may try a higher dose to experience a more potent sedative effect. The dose should never exceed 400mg per day. When using an excessively high dose, it is crucial to understand what Phenobarbital does to the human body, especially when the average Phenobarbital level is exceeded.

For Seizures

In cases where a patient suffers from seizures, up to 3mg per kilogram of body weight can be administered to the patient daily. The minimum recommended dose for treating seizures is 1mg. The dose is sometimes given during a single administration of the drug, but some physicians may prefer to split the dose in two. Either IV or oral administration of the medication can be used for treating seizures. The dose mentioned is used during the initial stages of treatment. An adjustment in the dosage is usually needed to help provide a more effective treatment to the patient.

man with seizures

For Substance Withdrawal

In some cases, this particular medication is also used to help assist a patient in the management of substance withdrawal symptoms. Individuals who have a dependency problem with benzodiazepines, as well as those with alcohol addiction, can stop using these substances and rely on Phenobarbital for a short period to assist with the withdrawal symptoms that they might experience.

When a person needs to use the drug for reducing substance withdrawal symptoms, the maximum recommended dose is 15mg of Phenobarbital per one kilogram of body weight. The minimum recommendation is 10mg. The drug is usually administered over half an hour.

For Medically-Induced Coma

There are certain cases where a patient would need to be placed into a medically-induced coma to assist with the management of a specific condition. Multiple barbiturates can be utilized to assist with this type of medical use.

Pediatric Dosages

The drug is sometimes used in pediatric cases as well. When the medication is used in children, a significantly lower dose is used, and there are also not as many cases in children where the drug is used as a treatment option compared to adults. Below is a list of the Phenobarbital pediatric dose for specific purposes.

For Seizures

Oral administration is provided in doses up to 20mg per one kilogram of body weight initially, followed by a recommended dose of up to 6mg per kilogram of weight. Parenteral administration can go as high as 15mg per kilogram of body weight.

For Sedation

When used as a sedative drug, up to 3mg of Phenobarbital can be administered per one kilogram of the child’s body weight. In most cases, this is a preoperative sedation method given through parenteral administration.


Phenobarbital is sometimes used as a treatment method, often combined with other techniques, in children with NAS, also known as Neonatal Abstinence Syndrome. The recommended form of the drug in such a case is an elixir. The dose is usually 4mg/mL.

Dosing Adjustments

Not only does the Phenobarbital long term side effects need to be considered when deciding to use the drug, but it is also essential to examine the results of the medication on certain parts of the body. In some instances, an adjustment to the dosage may be needed. For example, a 30mg dose may somewhat be adjusted to Phenobarbital 16.2mg in cases where a patient has a specific medical condition.


In case renal diseases are present, an adjustment could be made. While there are no guidelines provided, patients and physicians are advised to be cautious.


Individuals with a liver impairment will require an adjustment to their dose in some cases. Similar to the situation with renal problems, no guidelines have been specified. When severe liver impairment is noted, however, it is advised that the person does not use this particular drug at all.


The geriatric patient should use a lower dose than what is generally recommended as the body of such a person may be more sensitive to the drug.

senior woman taking phenobarbital

How To Take A Dose

Oral administration of the medication is usually advised to be taken once each day, but sometimes the dose may be divided into two separate dosages. The tablet is often taken at bedtime, but a physician may advise a person to take the drug at a different time of the day. It is not required to take the medicine with food. Some people may experience sensitivity to the drug. In such a case, it would be a better idea to use the medication with food. Milk can also be taken along with the pill instead.

What If One Missed A Dose Of Phenobarbital

When missing a dose of this drug, it is advised that a person takes it as soon as they remember. At the same time, however, when the time is too close to the individual’s next dose, it might be better to wait. Taking too much of the drug can cause more severe side-effects. Taking two doses too close to each other can also cause the risk of adverse events to increase.

Lethal Dose Of Phenobarbital

Generally, the drug tends to pose as deadly when administered in a range between two to 10 grams of Phenobarbital per one kilogram of the patient’s body weight.

Warnings, Precautions, And Contraindications

As part of Phenobarbital classification, the drug is considered to be a narrow therapeutic index substance. What this means is just a slight mistake in dosage can cause a person to suffer severe adverse effects. It is generally not advised to utilize a generic substitution for this drug. Furthermore, frequent monitoring needs to be conducted to avoid toxicity.

Exact dosage of Phenobarbital is required for certain conditions to avoid complications and yield valid results. It is crucial to understand that even the slightest difference in the administration of the drug may produce adverse reactions that can be severe. The medication does, however, yield fruitful results in different scenarios.

On the other hand, it does not make this drug less habit-forming. People with developed dependence on Luminal should seek help in drug addiction centers. Caring and qualified professionals will make sure to provide all the necessary treatment options to the patients and their family members.

Page Sources

  1. Anita Siu, Christine A. Robinson. Neonatal Abstinence Syndrome: Essentials for the Practitioner. J Pediatr Pharmacol Ther. 2014 Jul-Sep; 19(3): 147–155. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4187528/
  2. Ali H. Turhan, Aytug Atici, Cetin Okuyaz, Sercan Uysal. Single Enteral Loading Dose of Phenobarbital for Achieving Its Therapeutic Serum Levels in Neonates. Croat Med J. 2010 Jun; 51(3): 215–218. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2897089/

Published on: March 13th, 2024

Updated on: March 20th, 2024

About Author

Roger Weiss, MD

Dr. Roger Weiss is a practicing mental health specialist at the hospital. Dr. Weiss combines his clinical practice and medical writing career since 2009. Apart from these activities, Dr. Weiss also delivers lectures for youth, former addicts, and everyone interested in topics such as substance abuse and treatment.

Medically Reviewed by

Dr. Ash Bhatt

Throughout his professional life, Dr. Bhatt has been conferred with diplomate status by the American Board of Psychiatry and Neurology, certifying him in both adult and child/adolescent psychiatry. His experiences in emergency rooms, frequently encountering patients with simultaneous health and addiction issues, directed his attention to these specific fields.


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