Drug reference

phenobarbitone

Drug monograph

CDSCO approved

EXCRETION

—

not curated

INTERACTIONS

4 major

SEVERE in our sources

PREGNANCY

—

not curated

Top interactionssee all 12 →

CimetidineSevereTextbookKDT 7e · p650
CyclosporineSevereTextbookKDT 7e · p15
DigoxinSevereTextbookKDT 7e · p15
GriseofulvinSevereTextbookKDT 7e · p791

Mechanism

Not yet extracted

Indications

epilepsyadjuvant in psychosomatic disordersgeneralized tonic-clonic seizures (GTC)simple partial seizures (SP)complex partial seizures (CP)status epilepticus (slow response)

Dosing

Adult: 30–60 mg oral OD–TDS; 100–200 mg i.m./i.v.
Pediatric: 3–5 mg/kg/day

Pharmacokinetics

Half-life

80–120 hours

Protein binding

20%

Metabolism

Hepatic microsomal enzyme induction

Excretion

Significantly excreted unchanged in urine. Alkalinization of urine increases ionization and excretion.

Contraindications

obstructive sleep apnoea
absence seizures

Side effects

Common

hangover (dizziness, distortions of mood, irritability and lethargy)mental confusionimpaired performancetraffic accidentstolerancedependencesedationdullness

Serious

various malformations (teratogenic)
excitement (idiosyncrasy, more common in elderly)
precipitation of porphyria
hypersensitivity (rashes, swelling of eyelids, lips)
withdrawal symptoms (excitement, hallucinations, delirium, convulsions, deaths)
behavioral abnormalities
diminution of intelligence
impairment of learning and memory
hyperactivity in children
mental confusion in older people
rashes
megaloblastic anaemia
osteomalacia

Drug interactions

Cimetidine

Severe

Textbook

Phenobarbitone can accumulate to toxic levels.

Source: KDT 7e · p650

Cyclosporine

Severe

Textbook

Reduced oral bioavailability of cyclosporine.

Source: KDT 7e · p15

Digoxin

Severe

Textbook

Reduced oral bioavailability of digoxin.

Source: KDT 7e · p15

Griseofulvin

Severe

Textbook

Failure of griseofulvin therapy may occur.

Source: KDT 7e · p791

Calcitriol

Moderate

Textbook

Prolonged use can cause rickets/osteomalacia.

Not explicitly stated, but implies monitoring bone health and vitamin D status, and possibly increasing calcitriol dose or supplementing calcium.

Source: KDT 7e · p343

Carbamazepine

Moderate

Textbook

Reduced carbamazepine levels.

Source: KDT 7e · p416

Chloramphenicol

Moderate

Textbook

Reduced chloramphenicol concentration, potentially leading to failure of therapy.

Monitor chloramphenicol concentration and clinical response; adjust chloramphenicol dose if needed.

Source: KDT 7e · p741

Dexamethasone

Moderate

Textbook

Decreased therapeutic effect of dexamethasone.

The dose of dexamethasone may need to be adjusted upwards, or alternative corticosteroids that are less affected by enzyme induction should be considered.

Source: KDT 7e · p287

Ethinylestradiol

Moderate

Textbook

Contraceptive failure may occur.

Switch over to a preparation containing 50 µg of ethinylestradiol or use an alternative method of contraception.

Source: KDT 7e · p326

Folic Acid

Moderate

Textbook

Phenobarbitone can cause megaloblastic anaemia due to folate deficiency. Folic acid given in large doses can reduce the efficacy of phenobarbitone, increasing seizure risk.

Treat anticonvulsant-induced megaloblastic anaemia with folic acid, but avoid large doses to prevent antagonism of the anticonvulsant effect. Monitor folate levels and seizure control.

Source: KDT 7e · p610

Hydrocortisone

Moderate

Textbook

Decreased therapeutic effect of hydrocortisone.

The dose of hydrocortisone may need to be adjusted upwards, or alternative corticosteroids that are less affected by enzyme induction should be considered.

Source: KDT 7e · p287

Imipramine

Moderate

Textbook

Complex and unpredictable changes in imipramine levels/effects.

Source: KDT 7e · p401