Phenobarbital Dosage

Medically reviewed by Drugs.com. Last updated on Nov 29, 2024.

Usual Adult Dose for Sedation

Daytime Sedation:
30 to 120 mg orally, IM, or IV in 2 or 3 divided doses
Maximum dose: 400 mg during a 24-hour period

Preoperative Sedation:
Parenteral:
100 to 200 mg IM 60 to 90 minutes before surgery

Comments:

• Frequency of administration should be determined by the patient response.
• Parenteral administration should be reserved for situations in which oral administration is impossible/impractical.

Uses: Daytime sedation; preoperative sedation

Usual Adult Dose for Insomnia

Oral:

• Recommended dose: 100 to 200 mg orally once a day
• Maximum dose: 400 mg during a 24-hour period

Parenteral:

• Recommended dose: 100 to 320 mg IM or IV once a day
• Maximum dose: 400 mg during a 24-hour period

Comments:

• This drug may begin to lose effectiveness for inducing and maintaining sleep after 2 weeks.

Uses: Bedtime hypnosis; hypnosis

Usual Adult Dose for Seizures

Acute Convulsions
Parenteral:
20 to 320 mg IM or IV every 6 hours as necessary

Anticonvulsant:
Oral:
60 to 200 mg orally per day

Comments:

• Maintenance doses should be determined by clinical laboratory reference values.
• Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Treatment of generalized and partial seizures; treatment/prophylaxis of febrile seizures

Usual Pediatric Dose for Seizures

Anticonvulsant:
Oral:

• Initial dose: 15 to 20 mg/kg orally
• Recommended dose: 3 to 6 mg/kg orally

Parenteral:
4 to 6 mg/kg/day for 7 to 10 days or 5 to 15 mg/kg/day IM or IV

Status epilepticus:
Parenteral:

• Initial dose: 15 to 20 mg/kg IV over 10 to 15 minutes

Comments:

• Loading doses of 15 to 20 mg/kg are predicted to produce blood levels of approximately 20 mcg/mL after administration.
• Maintenance doses should be determined by clinical laboratory reference values.
• Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Anticonvulsant used for the treatment of generalized and partial seizures, treatment/prophylaxis of febrile seizures, and treatment of status epilepticus.

Usual Pediatric Dose for Sedation

Parenteral:
1 to 3 mg/kg IM or IV

Use: Preoperative sedation

Renal Dose Adjustments

Dose adjustments may be required; however, no specific guidelines have been suggested. Caution recommended.

Liver Dose Adjustments

Mild to moderate liver impairment: Dose adjustments may be required; however, no specific guidelines have been suggested. Caution recommended.
Marked/severe liver impairment: Contraindicated

Dose Adjustments

• Geriatric or debilitated patients: This drug should be used at a reduced dosage due to an increased risk of sensitivity; however, no specific dose adjustment guidelines have been suggested.
• Clinical laboratory reference values should be used to determine the therapeutic anticonvulsant level of phenobarbital in serum.
• To achieve the blood levels considered therapeutic in children, higher per kg doses are generally necessary.

Therapeutic drug range: 5 to 40 mcg/mL (sedation)

Precautions

NARROW THERAPEUTIC INDEX:

• This drug should be considered a narrow therapeutic index (NTI) drug as small differences in dose or blood concentrations may lead to serious therapeutic failures or adverse drug reactions.

Recommendations:

• Generic substitution should be done cautiously, if at all, as current bioequivalence standards are generally insufficient for NTI drugs.
• Additional and/or more frequent monitoring should be done to ensure receipt of an effective dose while avoiding unnecessary toxicities.

Consult WARNINGS section for additional precautions.

US Controlled Substance: Schedule IV

Dialysis

Data not available

Other Comments

Administration advice:

• The IV formulation should be diluted prior to use and the infusion rate should not exceed 60 mg/min in adults.
• If given IM, limit the volume to 5 mL per site. Injections should be administered deeply into large muscles.

Storage requirements:

• The manufacturer product information should be consulted.

Reconstitution/preparation techniques:

• The manufacturer product information should be consulted.

General:

• If discontinuation is necessary, this drug should be withdrawn slowly to prevent seizures or status epilepticus.
• Dosing should be based on a patient's age, weight, and condition.
• Anticonvulsant activity is believed to be present at sub-hypnotic doses.

Monitoring:

• Blood pressure, respiration, and cardiac function during IV administration or IM (at hypnotic doses).
• Hematopoietic, renal and hepatic function periodically, especially during long-term therapy.
• Bone mineral density, especially during prolonged treatment.

Patient advice:

• Advise patients, and families/caregivers to monitor and report signs/symptoms of suicidality, and/or unusual behavior immediately to their healthcare provider (e.g., agitation, irritability, anxiety, panic attacks, insomnia, hostility, aggressiveness, impulsivity, akathisia, hypomania/mania).
• Patients should be cautioned about performing activities requiring mental alertness, such as operating hazardous machinery or a motor vehicle, until they are reasonably certain that this drug does not adversely affect them.
• Patients should be told to avoid consuming alcohol while taking this drug.
• Instruct patients to immediately report any signs/symptoms of Stevens-Johnson syndrome, toxic epidermal necrolysis, hematological disease, or hypersensitivity reactions.
• Patients should be advised to report all concurrent prescription and nonprescription medications or herbal products they are taking.
• Advise patients to speak to their healthcare provider if they become pregnant, intend to become pregnant, or are breastfeeding.

See also:

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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