Drug Index


Synonym :


Mechanism :

Phenobarbital is a barbiturate, nonselective central nervous system depressant which is primarily used as a sedative hypnotic and also as an anticonvulsant in subhypnotic doses.

Indication :

  • Epilepsy
  • Status epilepticus
  • Hyperbilirubinemia of new born (off-label)
  • Pruritus
  • Cerebral irritation - acute cerebral event
  • Intractable seizures in terminal period
  • Sedative
  • Hypnotic
  • Neonatal seizure(orphan)
  • Encephalopathy (orphan)

Contraindications :

Phenobarbitone is contraindicated in patients with known phenobarbital sensitivity or a history of manifest or latent porphyria. Reduce dose and monitor levels in renal and liver disease. Warn of drowsiness particularly at start of treatment and not to cease therapy without advice. Drowsiness is enhanced by alcohol.

Dosing :


Loading dose: 15-20 mg/kg orally, IV or IM.


Neonates: 3-5 mg/kg/24 hours oral or IV in 2 divided doses or as single daily dose.

Infants: 5-6 mg/kg/24 hours oral or IV in 2 divided doses or as single daily dose.

1-5 years: 6-8 mg/kg/24 hours oral or IV in 2 divided doses or as single daily dose.

6-12 years: 4-6 mg/kg/24 hours in 2 divided doses or as single daily dose.

>12 years 1-3 mg/kg/24 hours oral or IV in 2 divided doses or as single daily dose.


2 mg/kg orally thrice daily.


3-5 mg/kg orally at bed time.

Hyperbilirubinemia (off-label):

Neonates: 5 mg/kg/day oral/IV as a single dose or twice daily. Not widely used as phototherapy usually suffices.

Adverse Effect :

Dose dependent: Sedation, ataxia, dizziness, drowsiness, nystagmus, irritability, paraesthesia, restlessness and cardiac and respiratory depression. Cognitive dysfunction, behaviour change occurs on chronic use.

Interaction :

Anticoagulants: Phenobarbital lowers the plasma levels of dicumarol and causes a decrease in anticoagulant activity as measured by the prothrombin time.
Corticosteroids: Phenobarbital appears to enhance the metabolism of exogenous corticosteroids probably through the induction of hepatic microsomal enzymes.
Griseofulvin: Phenobarbital appears to interfere with the absorption of orally administered griseofulvin, thus decreasing its blood level.
Doxycycline: Phenobarbital has been shown to shorten the half- life of doxycycline.
Phenytoin, Sodium Valproate, Valproic Acid: The effect of phenobarbital on the metabolism of phenytoin appears to be variable. Some investigators report an accelerating effect, while others report no effect.
Central Nervous System Depressants: The concomitant use of other central nervous system depressants including other sedatives or hypnotics, antihistamines, tranquilizers, or alcohol may produce additive depressant effects.
Monoamine Oxidase Inhibitors (MAOIs): MAOIs prolong the effects of phenobarbital probably because metabolism of the phenobarbital is inhibited.
Estradiol, Estrone, Progesterone and other Steroidal Hormones: Pre-treatment with or concurrent administration of phenobarbital may decrease the effect of estradiol by increasing its metabolism.

Renal Dose :

Dose in Renal Impairment GFR (mL/min)
20-50Dose as in normal renal function
10-20Dose as in normal renal function, but avoid very large doses
<10Reduce dose by 25–50% and avoid very large single doses

Dose in Patients undergoing Renal Replacement Therapies
CAPDDialysed. Dose as in GFR<10 mL/ min
HDDialysed. Dose as in GFR<10 mL/ min
HDF/High fluxDialysed. Dose as in GFR<10 mL/ min
CAV/VVHDNot dialysed. Dose as in GFR=10– 20 mL/min

Hepatic Dose :

Phenobarbital exposure is increased with hepatic impairment and can lead to coma; reduced doses are recommended; use with caution.
03/24/2024 11:44:26 Phenobarbitone
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