Phenobarbital

Actions

• Prolongs GABA-mediated chloride channel openings.
• Blocks kainate receptors.

Metabolism

Hepatic

Enzymes involved

• CYP2C9

Elimination

Renal and fecal

Enzyme induction

• CYP1A2
• CYP2A6
• CYP2B6
• CYP2C8
• CYP2C9
• CYP3A4

Therapeutic serum concentration range

20-40 μg/ml

Half-life

72-124 hours

Plasma protein binding

20-45%

Important side-effects

Serious dermatologic reactions including Stevens-Johnson syndrome and TEN.

CNS depression.

Indications

Generalized and focal seizures.

Not effective against absence seizures.

Dosing recommendation

Start with 30–50 mg at bedtime.

Increase, if indicated, after 10–15 days

Target dose: 50–200 mg/day in a single dose.

Renal impairment

Careful titration and monitoring of serum concentration is advised in patients with impaired renal function.

Hepatic impairment

Careful titration and monitoring of serum concentration is advised in patients with impaired hepatic function.

Serum concentration changes during pregnancy

Total level decreases by 20%. Free fraction level decreases by 10-20%.