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.

Further information

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

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