Phenobarbital pharmacokinetics and bioavailability in adults

Area of Science:

• Pharmacology
• Clinical Pharmacy

Background:

• Phenobarbital is a widely used antiepileptic drug.
• Understanding its pharmacokinetic profile is crucial for optimizing therapeutic efficacy and safety.

Purpose of the Study:

• To determine the pharmacokinetics and bioavailability of phenobarbital in healthy adult subjects.
• To assess phenobarbital absorption and elimination following intravenous and oral administration.

Main Methods:

• Six healthy adult subjects received single intravenous (2.6 mg/kg) and oral (2.9 mg/kg) doses of phenobarbital.
• Serum phenobarbital concentrations were measured using high-pressure liquid chromatography over 21 days.
• Pharmacokinetic parameters including half-life, clearance, and volume of distribution were calculated.

Main Results:

• The mean elimination half-life was 5.8 days after IV dose and 5.1 days after oral dose.
• Absolute oral bioavailability was high, averaging 94.9% (range 81-111.9%).
• No evidence of phenobarbital autoinduction was observed during the study period.

Conclusions:

• Phenobarbital is well absorbed orally, exhibiting high bioavailability.
• The drug has a long elimination half-life, consistent with its sustained therapeutic effects.
• These findings support the established dosing regimens for phenobarbital in clinical practice.